1 Scope
NOTE This standard covers the materials, design basis, installation, testing, and warranty requirements for single-ply low-slope membrane roof systems on commercial, institutional, and industrial buildings. (1.1)
NOTE The three membrane technologies addressed — thermoplastic polyolefin (TPO), polyvinyl chloride (PVC), and ethylene propylene diene monomer (EPDM) — collectively represent the dominant choices in the low-slope roofing market and share a common design and installation logic even though their chemical composition and seaming methods differ. (1.2)
NOTE Governing this standard as a unified document promotes consistent detailing, submittal practice, and quality-assurance rigor across all three technologies rather than treating each as a wholly separate scope. (1.3)
1.4 System Basis
NOTE The membrane, insulation, cover board, vapor retarder, fasteners, flashings, edge metal, and accessories function together as an integrated assembly whose performance — thermal, wind-uplift, fire, and waterproofing — depends on the compatibility and correct installation of every component. (1.4.1)
NOTE A membrane that meets its material standard but is installed over incompatible insulation, fastened at the wrong spacing, or terminated with undersized edge metal can fail despite the quality of its constituent parts. (1.4.2)
NOTE Low-slope membrane roofing is a building-envelope system, not merely a waterproofing layer. (1.4.3)
1.4.4 The entire roofing assembly shall be designed and installed as a system, with every component selected from an FM-approved or UL-classified assembly that has been tested as a unit.
1.5 Applicable Slopes
NOTE The maximum 3:12 limit reflects the practical performance ceiling for ballasted systems and the increased tendency for fully adhered membranes to slip on steeper substrates; slopes above 3:12 require a different roofing technology. (1.5.1)
NOTE Ponded water accelerates membrane degradation, imposes sustained structural loads not included in typical roof-deck design, and constitutes a code violation under IBC Section 1503.4. (1.5.2)
1.5.4 Where the deck slope is below 1/4:12, the roof shall be redesigned with tapered insulation or crickets to achieve positive drainage.
1.5.5 Single-ply membrane shall not be installed on a net-zero slope deck.
1.6 Contractor Certification
NOTE The membrane manufacturer requires an approved contractor status as a precondition for issuance of a No Dollar Limit (NDL) warranty. (1.6.1)
1.6.2 The Contractor shall hold a current, manufacturer-issued certification or qualification for the membrane system being installed prior to commencing work.
NOTE This certification requirement is not waivable and applies regardless of the Contractor's general roofing experience. (1.6.3)
2 Referenced Standards
2.1 All materials, design, and installation shall conform to the latest adopted edition of the following standards unless a specific edition is cited as the controlling document by the Authority Having Jurisdiction or the Owner's insurance carrier.
NOTE Where conflict exists between standards, the more stringent requirement governs unless the Engineer of Record directs otherwise in writing. (2.2)
| Standard |
Title |
| ASTM D6878/D6878M |
Standard Specification for Thermoplastic Polyolefin-Based Sheet Roofing |
| ASTM D4434/D4434M |
Standard Specification for Poly(Vinyl Chloride) Sheet Roofing |
| ASTM D4637/D4637M |
Standard Specification for EPDM Sheet Used in Single-Ply Roof Membrane |
| ASTM C1289 |
Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board |
| ASTM C1177 |
Standard Specification for Glass Mat Gypsum Substrate for Use as Sheathing |
| ASTM C728 |
Standard Specification for Perlite Thermal Insulation Board |
| ASTM E108 |
Standard Test Methods for Fire Tests of Roof Coverings |
| UL 790 |
Standard Test Methods for Fire Tests of Roof Coverings (equivalent to ASTM E108) |
| ASTM D1970 |
Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection |
| FM Global Data Sheet 1-28 |
Wind Design |
| FM Global Data Sheet 1-29 |
Roof Deck Securement and Above-Deck Roof Components |
| FM 4470 |
Standard for Class 1 and Class 1 Noncombustible Construction — Roofing |
| FM 4474 |
American National Standard for Evaluation of Simulated Wind Uplift Resistance of Roof Assemblies Using Static Positive and/or Negative Differential Pressures |
| ANSI/SPRI/FM 4435/ES-1 |
Wind Design Standard for Edge Systems Used with Low Slope Roofing Systems |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
| NRCA Roofing Manual |
Low-Slope Membrane Roof Systems |
| IBC |
International Building Code — Chapter 15 (Roof Assemblies and Rooftop Structures) |
| ASHRAE 90.1 |
Energy Standard for Buildings Except Low-Rise Residential Buildings |
| SMACNA Architectural Sheet Metal Manual |
Current Edition |
3 Submittals
3.1 Action Submittals
3.1.1 Contractor shall submit the following for review and approval before procuring materials or beginning installation.
3.1.2 The membrane, insulation, and edge-metal submittals are interdependent; they shall be submitted together as a single package so that the assembly can be verified as a listed, tested system rather than reviewed component by component.
- Product data sheets for the membrane (TPO, PVC, or EPDM), confirming ASTM compliance, nominal and minimum thickness, reinforcement type, tensile and seam strength, and applicable FM approval number and UL classification
- Product data sheets for all insulation layers, cover board, and vapor retarder, including FM-approved assembly numbers for which those products are a component
- Product data sheets for membrane adhesive, seam primer, seam tape (EPDM), field-applied lap sealant, and all accessory items (pipe boots, walkway pads, termination bar, pitch pockets, cants)
- Current FM RoofNav assembly listing confirmation for the complete as-specified assembly, including deck type, insulation type and thickness, cover board, attachment method, and fastener pattern, confirming the wind-uplift rating equals or exceeds the design requirement
- UL fire-classification listing confirmation for the complete assembly on the specified deck type
- ANSI/SPRI ES-1 test reports for all perimeter edge metal and coping cap systems, confirming the tested wind pressure meets or exceeds the design edge-zone pressure from ASCE 7
- Shop drawings for all perimeter edge metal, coping caps, and scuppers, showing dimensions, gauges, joinery, and expansion joint locations
- Contractor's current manufacturer authorization or certification certificate
- Manufacturer's standard warranty form and any supplemental requirements for NDL warranty eligibility
☐ Membrane product data (ASTM compliance, thickness, FM/UL listing)
☐ Insulation, cover board, and vapor retarder product data
☐ Adhesive, primer, seam tape, lap sealant, and accessory product data
☑ FM RoofNav assembly listing confirmation
☑ UL fire-classification listing confirmation
☑ ANSI/SPRI ES-1 test reports for edge metal and coping
☐ Shop drawings for edge metal, coping caps, and scuppers
☐ Contractor manufacturer authorization certificate
☐ Manufacturer warranty form and NDL eligibility requirements
● TPO (thermoplastic polyolefin) — ASTM D6878
○ PVC (polyvinyl chloride) — ASTM D4434
○ EPDM (ethylene propylene diene monomer) — ASTM D4637
3.2 Closeout Submittals
3.2.1 Contractor shall provide the following at substantial completion before the roofing system is accepted and before the membrane warranty is issued.
- Manufacturer's warranty, executed and dated, covering the complete roofing assembly for the specified warranty term
- Contractor's installation warranty
- Manufacturer's pre-warranty inspection report, if required by the manufacturer as a condition of warranty issuance
- Field test reports for all flood tests, core cuts, and electronic leak detection surveys performed during or after installation
- As-installed drawings showing the layout of membrane panels, seam locations, drain locations, and locations of all penetrations and curbs
- Material certifications confirming that all membrane rolls and insulation boards used on the project conform to the specified ASTM standards
☑ Manufacturer's executed and dated warranty
☑ Contractor's installation warranty
☐ Manufacturer pre-warranty inspection report (if required)
☐ Field test reports (flood test, core cuts, ELD)
☐ As-installed drawings (panels, seams, drains, penetrations, curbs)
☑ Material certifications confirming ASTM conformance
4 Quality Assurance
4.1 Contractor Qualifications
NOTE Manufacturer authorization is typically renewed annually and requires demonstrated completion of manufacturer-sponsored training and a minimum volume of satisfactory installations. (4.1.1)
4.1.2 The Contractor shall be an authorized, trained installer, certified or approved by the membrane manufacturer for the system being installed.
4.1.3 The Contractor shall submit evidence of current authorization before the submittal package is approved.
NOTE The use of an unauthorized installer voids any manufacturer warranty and is cause for rejection of the work. (4.1.4)
4.1.5 The roofing foreman assigned to this project shall have a minimum of five years of documented field experience with the membrane type being installed.
4.1.6 Where hot-air welding of thermoplastic membranes is required, the welding operator(s) shall be trained on the specific hot-air welder model being used and shall demonstrate proficiency by producing acceptable test welds before production welding begins.
4.2 Pre-Installation Conference
4.2.1 A pre-installation conference shall be held before the start of roofing work, attended by the Contractor, the Contractor's roofing foreman, the membrane manufacturer's technical representative, the Owner or Owner's representative, and the Architect or Engineer.
4.2.2 The conference shall cover the approved submittal assembly, the sequencing of work, vapor retarder installation (if required), deck inspection and acceptance criteria, field quality-control procedures, warranty requirements, and coordination with other trades that penetrate or load the roof membrane.
4.2.3 The Contractor shall prepare and distribute meeting minutes within five business days.
4.3 Manufacturer's Technical Representative
4.3.1 For projects that carry an NDL warranty, the membrane manufacturer's technical representative shall visit the project site at minimum intervals tied to the installation milestones below.
4.3.2 The technical representative shall visit at the start of membrane installation to observe and approve the substrate and initial installation procedures.
4.3.3 The technical representative shall visit at the mid-point of membrane installation to observe seaming quality, flashing progress, and fastener patterns.
4.3.4 The technical representative shall visit at substantial completion, prior to issuing the warranty, to perform the manufacturer's final inspection.
4.3.5 Representative site visit reports shall be included in the closeout submittal.
4.4 Field Mock-Up
4.4.1 Where the project is large enough to warrant it (typically 20,000 square feet of new membrane or more, or at the Owner's direction), the Contractor shall install a field mock-up panel before beginning production installation.
4.4.2 The Contractor shall install a field mock-up panel of at least 100 square feet before beginning production installation.
4.4.3 The mock-up shall include at least one field seam, one T-joint, one flashing termination at a vertical wall, and one penetration pipe boot.
4.4.4 The mock-up shall be reviewed and accepted by the Architect, Owner's representative, and manufacturer's technical representative before production work proceeds.
4.4.5 The mock-up may remain as part of the finished work if it passes inspection.
4.5 Listing and Labeling
4.5.1 All roofing materials and accessories shall be labeled or identified with the applicable listed assembly information.
4.5.2 Membrane rolls shall bear the manufacturer's product name, thickness, ASTM designation, and applicable FM approval or UL classification.
4.5.3 Insulation boards shall be labeled with ASTM designation, R-value, and manufacturer's lot number.
4.5.4 Edge metal that is required to meet ANSI/SPRI ES-1 shall be labeled, tagged, or delivered with documentation confirming the ES-1 test classification.
5 Environmental and Substrate Conditions
5.1 Temperature Restrictions
NOTE Cold-weather installation increases the risk of membrane stiffness, incomplete adhesive bond, and inadequate seam welds. (5.1.1)
● 40°F ambient and substrate (standard practice)
○ Below 40°F with manufacturer-approved cold-weather procedures
5.1.2 Membrane installation shall not proceed when the ambient air temperature or the substrate temperature is below 40°F (4°C) for thermoplastic (TPO, PVC) systems or below 40°F for EPDM adhesive applications, unless the membrane manufacturer has specifically approved cold-weather procedures and those procedures are submitted and accepted.
5.1.3 Where cold-weather installation is unavoidable, the Contractor shall use membrane adhesives and accessories formulated for cold-temperature application, pre-condition membrane rolls in a heated space to at least 50°F before deployment, and protect the work area from wind and precipitation.
5.1.4 Installation shall not proceed during rain, snow, or fog, or when the deck surface is wet or frost-covered.
5.1.5 Membrane adhesive application shall not proceed when relative humidity exceeds the adhesive manufacturer's published limit.
5.1.6 All dew and condensate shall be removed from the deck before installation.
5.1.7 Pond water remaining on an existing roof surface shall be removed completely before any re-cover or replacement work proceeds.
5.2 Deck Acceptance
5.2.1 The Contractor shall inspect the roof deck before installing any membrane assembly components and shall not proceed until the deck meets the conditions below.
NOTE Proceeding over a deficient deck is not a latent condition for warranty purposes; the Contractor assumes responsibility for any deficiency that is not reported before installation. (5.2.2)
Structural steel deck — 22 gauge or heavier
Structural steel deck — lighter than 22 gauge (verify fastener pull-out)
Cast-in-place or precast concrete
Lightweight insulating concrete over steel deck
Wood structural panel (plywood or OSB)
Gypsum structural concrete
Per drawings
5.2.3 Steel deck shall be free of rust, oil, paint, and surface contamination that would impair adhesion or fastener pull-out strength, and all deck-to-structural framing attachments shall be tight.
5.2.4 Any loose, deflected, or damaged steel deck panels shall be reported and corrected by others.
5.2.5 Concrete decks shall be structurally sound, clean, and have a surface profile suitable for adhesive bonding or mechanical fastening, and cracks wider than 1/16 inch shall be documented and reported.
5.2.6 Wood or lightweight concrete decks shall be assessed for fastener pull-out value per FM Global Data Sheet 1-29 if the fastener pull-out value assumed in the wind-uplift design has not been verified by prior testing for the specific deck type and condition.
5.2.7 The Contractor shall document in writing any deck deficiency observed and shall not proceed on affected areas until the deck has been corrected and re-inspected.
5.3 Slope and Drainage
5.3.1 The roof drainage system design — number, size, and location of primary and overflow drains — is the responsibility of the Designer of Record and shall be coordinated with the structural engineer (overflow drainage design load), the plumbing engineer (drain sizing), and the civil or landscape engineer (discharge routing).
○ Slope inherent in structural framing — no tapered insulation required
● Tapered insulation system — design by insulation manufacturer
○ Combination: structural slope supplemented with tapered insulation
5.3.3 On structural decks where the framing geometry does not provide this minimum slope throughout, the Contractor shall provide tapered insulation panels designed by the insulation manufacturer to achieve the required slope.
5.3.4 The tapered insulation design shall be coordinated with the structural engineer when additional dead load affects the structure.
5.3.5 Crickets shall be provided behind curbs, equipment supports, and other roof obstructions that would otherwise create areas of ponded water.
6 Wind Uplift and Fire Design Basis
6.1 Wind Uplift Design
6.1.1 The zone pressures established by the Designer of Record are the governing design values; the FM-classified assembly and edge metal shall meet or exceed them.
NOTE Perimeter and corner zones require closer fastener spacing or additional rows of fasteners than the field zone. (6.1.3)
FM 1-60 (60 psf)
FM 1-90 (90 psf)
FM 1-120 (120 psf)
FM 1-150 (150 psf)
FM 1-180 (180 psf)
Per engineering calculation — not FM classified
Per drawings
● FM Global — FM-approved assembly required (RoofNav listing)
○ ASCE 7 / IBC — engineered attachment per manufacturer testing
6.1.4 Wind-uplift design for the roofing assembly shall comply with ASCE 7, Chapter 26 and Chapter 27 (or Chapter 30 for components and cladding), as adopted by the applicable building code.
6.1.5 The Designer of Record shall establish the design wind pressures for field, perimeter, and corner zones of the roof based on the building's risk category, mean roof height, exposure category, and basic wind speed from the applicable wind speed map.
6.1.6 Where the Owner's property insurance is underwritten by FM Global, the roofing assembly shall carry an FM approval rating equal to or exceeding the FM wind-uplift design value calculated per FM Global Data Sheet 1-28.
6.1.7 The FM RoofNav database shall be the source of assembly listings, and all components (deck, insulation, cover board, membrane, fasteners, and attachment pattern) shall match the listed assembly.
NOTE Substituting components not in the listed assembly voids the FM classification. (6.1.8)
6.1.9 Where FM Global insurance does not govern, the Contractor shall select assemblies that have been tested per FM 4474 or per the membrane manufacturer's published engineering data, and shall verify that the calculated field, perimeter, and corner pressures are within the tested capacity at the specified fastener and plate spacing and pattern.
6.1.11 The Contractor shall not reduce the specified fastener density in any zone without written approval from the Designer of Record and confirmation that the reduced pattern maintains the required FM or engineered uplift capacity.
NOTE ES-1 classifies edge metal by the wind pressure it can resist (RE-1, RE-2, and RE-3 test methods for displacement, blow-off, and securement, respectively). (6.2.1)
30200
45607590105120150200
Default: 75 psf
Per drawings
6.2.2 Perimeter edge metal — including coping caps, gravel stops, fascia, and drip edge — shall be designed and tested in accordance with ANSI/SPRI/FM 4435/ES-1 for resistance to the design wind pressure in the building's perimeter and corner edge zones.
6.2.3 The specified edge metal assembly shall carry an ES-1 classification rating that meets or exceeds the design edge-zone wind pressure.
6.2.4 IBC Section 1504.5 mandates ES-1 compliance for metal edge securement on low-slope roofs, and this requirement cannot be waived.
6.2.5 The edge-zone design wind pressure shall be calculated from the ASCE 7 components-and-cladding provisions for the roof perimeter.
6.2.6 The Designer of Record shall state the design edge pressure on the drawings; the Contractor shall confirm that the specified ES-1-rated edge metal meets that pressure before procurement.
6.3 Fire Classification
NOTE The classification is an assembly classification, not a membrane-only property; insulation type, cover board, and deck type all influence the fire performance, and substituting any component requires re-confirmation that the new assembly retains the required classification. (6.3.1)
NOTE IBC Table 1505.1 establishes minimum classification (Class A, B, or C) based on construction type. (6.3.2)
● Class A — effective against severe fire exposure (most commercial buildings)
○ Class B — effective against moderate fire exposure
○ Class C — effective against light fire exposure
6.3.3 The roofing assembly shall achieve the fire classification required by IBC Section 1505 for the building's occupancy and construction type.
6.3.4 Classification shall be demonstrated by a current UL or listing-agency classification under ASTM E108 / UL 790 for the complete assembly on the specified deck type.
6.3.5 All project-specific deck and assembly combinations shall be confirmed against the membrane manufacturer's published classified assemblies.
NOTE Single-ply membranes installed over combustible decks require particular attention because the deck's contribution to burning-brand penetration is significant. (6.3.6)
7 Membrane Materials
7.1 TPO Membrane — ASTM D6878
NOTE TPO is a reinforced, heat-weldable, single-ply thermoplastic membrane whose field seams and all flashing terminations are made using hot-air welding equipment. (7.1.1)
NOTE TPO membrane chemistry uses a base polyolefin polymer (typically polypropylene or a polypropylene/ethylene copolymer) with additives for UV stabilization, flexibility, and fire retardancy, and the membrane is reinforced with a woven polyester or fiberglass scrim. (7.1.2)
NOTE Heat-welded seams, when properly formed, create a bond equal to or stronger than the base membrane. (7.1.3)
○ 45 mil (minimum conforming to ASTM D6878)
● 60 mil (standard commercial specification)
○ 80 mil (high-durability; high-traffic or severe-exposure applications)
● 6 ft (standard for mechanically attached systems)
○ 10 ft (standard for fully adhered systems)
○ 12 ft
7.1.4 Thermoplastic polyolefin (TPO) membrane shall conform to ASTM D6878/D6878M, Standard Specification for Thermoplastic Polyolefin-Based Sheet Roofing.
7.1.5 No adhesive or tape seaming is permitted for field seams or flashing seams in TPO systems; all seams shall be hot-air welded.
7.1.6 ASTM D6878 requires a minimum breaking strength (tensile) of 220 lbf per in width and a minimum seam peel strength of 35 lbf per in width under dry conditions, providing the basis for the weld quality acceptance criteria in this standard.
NOTE The 60-mil thickness is the recommended default for most commercial projects; the 45-mil thickness meets the ASTM minimum but provides less puncture resistance and weld-quality margin and is suitable for lightly loaded, low-traffic roofs only, while the 80-mil thickness is appropriate for roofs with frequent maintenance traffic, heavy equipment loads, hail-prone climates, or extended service life without re-membrane. (7.1.7)
NOTE Narrower sheets in mechanically attached systems allow fastener-and-plate rows to be placed within seam overlaps at manageable spacing, while wider sheets in adhered systems reduce the number of seams and associated labor and reduce the number of fastener-and-plate rows in the insulation layers. (7.1.8)
7.2 PVC Membrane — ASTM D4434
NOTE PVC is a reinforced, heat-weldable thermoplastic membrane with a plasticizer system that provides flexibility at low temperatures. (7.2.1)
NOTE PVC membranes classified as Type II (fiber-reinforced), Type III (fabric-reinforced), or Type IV (fabric-reinforced with fabric backing) are all conforming under ASTM D4434. (7.2.2)
NOTE PVC contains plasticizers that can migrate over time into adjacent materials, particularly certain bituminous insulation facers and adhesives. (7.2.3)
○ Type II — fiber-reinforced
● Type III — fabric-reinforced
○ Type IV — fabric-reinforced with fabric backing
7.2.4 Polyvinyl chloride (PVC) membrane shall conform to ASTM D4434/D4434M, Standard Specification for Poly(Vinyl Chloride) Sheet Roofing.
7.2.5 Like TPO, all PVC field seams and flashing seams shall be hot-air welded.
7.2.6 The project shall specify the PVC type required by the FM-approved or UL-classified assembly.
7.2.7 ASTM D4434 requires a minimum of 16 mils of PVC compound over the scrim reinforcement on each face of the reinforcement layer.
7.2.8 All insulation, cover board, and adhesive products used with PVC membrane shall be confirmed by the manufacturer to be plasticizer-migration-compatible.
7.3 EPDM Membrane — ASTM D4637
NOTE EPDM is a vulcanized synthetic rubber membrane whose field seams are made with self-adhesive lap tape and seam primer, not hot-air welding. (7.3.1)
NOTE ASTM D4637 covers both non-reinforced and reinforced (fabric- or scrim-backed) EPDM sheet. (7.3.2)
NOTE Proper seam technique depends on surface preparation, adhesive primer application, and roll pressure during seam formation; unlike thermoplastic membranes, EPDM cannot be re-fused once vulcanized, and deviation from the published seam procedure is the leading cause of EPDM seam failure. (7.3.3)
7.3.4 Reinforced EPDM provides higher resistance to membrane tearing and is preferred for mechanically attached applications where the membrane must span between fastener rows without tearing, while non-reinforced EPDM has superior elongation and conforms more readily to complex flashing geometry.
○ 45 mil (minimum; light-duty applications only)
● 60 mil (standard commercial specification)
○ 90 mil (high-durability; hail-prone or high-traffic applications)
● Non-reinforced — superior elongation, preferred for adhered flashings
○ Reinforced (scrim- or fabric-backed) — preferred for mechanically attached systems
7.3.5 Ethylene propylene diene monomer (EPDM) membrane shall conform to ASTM D4637/D4637M, Standard Specification for EPDM Sheet Used in Single-Ply Roof Membrane.
7.3.6 All EPDM seam work shall follow the membrane manufacturer's current published installation instructions precisely.
7.3.7 The project shall specify whether non-reinforced or reinforced EPDM is required.
7.4 EPDM Reflectance and Cool-Roof Compliance
NOTE EPDM is inherently black and a highly effective UV absorber, which contributes to elevated roof surface temperatures relative to white or reflective membranes; white or light-gray TPO or PVC membranes generally have significantly higher initial solar reflectance. (7.4.1)
○ Yes — membrane reflectance must meet ASHRAE 90.1 or local code
● No — reflectance requirement waived or not applicable
7.4.2 Where energy codes require a minimum solar reflectance index (SRI) or cool-roof performance, the Designer of Record shall confirm whether EPDM satisfies the energy code requirement for the project's climate zone.
7.4.3 Where cool-roof compliance is required, the Contractor shall submit manufacturer-published or CRRC (Cool Roof Rating Council) tested reflectance and emittance values for the specified membrane.
7.4.4 EPDM systems that cannot meet the SRI requirement shall not be substituted for a TPO or PVC system that can without written approval from the Designer of Record.
8 Insulation and Cover Board
8.1 Polyisocyanurate Insulation
NOTE Polyiso is the predominant insulation type used beneath single-ply roofing membranes because of its high R-value per inch, its availability in tapered panels for drainage, and its broad listing in FM-approved and UL-classified roofing assemblies. (8.1.1)
NOTE ASTM C1289 classifies polyiso by type, class, and grade based on compressive strength, facer type, and thermal performance. (8.1.2)
NOTE For new roof construction, ASHRAE 90.1 requires continuous insulation values typically in the R-20 to R-30 range depending on climate zone. (8.1.3)
NOTE ASTM C1289 requires polyiso manufacturers to publish and certify long-term thermal resistance (LTTR) values using a 15-year time-weighted average procedure. (8.1.4)
1540
152025303540
Default: 25 R (h·ft²·°F/BTU)
Per drawings
● Two layers, staggered joints (minimum required)
○ Three or more layers (high-R assemblies)
● Fiber-reinforced felt (standard)
○ Coated glass fiber (improved moisture resistance)
○ Foil-faced (vapor barrier facer — coordinate with vapor retarder strategy)
8.1.5 Polyisocyanurate (polyiso) board insulation shall conform to ASTM C1289, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board.
8.1.6 The minimum insulation R-value shall comply with ASHRAE 90.1, Table C5.2 (or the corresponding table in the adopted energy code) for the project's climate zone.
8.1.7 Insulation shall be provided in a minimum of two layers with staggered joints in each direction so that no through joints in the insulation align with joints in an adjacent layer.
NOTE Single-layer insulation installation is not permitted because through-joint thermal bridging and wind-uplift stress concentrations at single-layer joints are both significantly worse than in a staggered two-layer installation. (8.1.8)
8.1.9 Contractors and designers shall use the long-term thermal resistance (LTTR) of polyisocyanurate insulation, not the aged or initial-test value, for code compliance demonstration.
8.2 Cover Board
NOTE NRCA and the major membrane manufacturers all recommend cover boards because polyiso's cellular foam surface does not provide adequate resistance to foot traffic, membrane adhesive absorption, and long-term compressive creep under fastener plates. (8.2.1)
NOTE A cover board also separates the membrane adhesive from the polyiso facer, preventing adhesive incompatibility and migration issues. (8.2.2)
● High-density polyiso cover board — ASTM C1289 Type II, Class 4 (80 psi minimum compressive strength)
○ Glass-mat gypsum board — ASTM C1177
○ Perlite board — ASTM C728 Type 2
○ High-density wood fiber board
8.2.3 A cover board shall be installed over the polyisocyanurate insulation in all fully adhered and mechanically attached membrane assemblies.
NOTE High-density polyiso cover board provides the best combination of compressive strength, thermal contribution, light weight, and compatibility with the polyiso insulation layers below it, and is the recommended default; glass-mat gypsum cover board provides a more dimensionally stable surface for adhered membranes and is preferred where the roof will receive frequent maintenance traffic or where the FM-approved assembly requires it; perlite board is an older, lower-compressive-strength material principally used in re-cover applications where it is already specified by the FM-approved assembly. (8.2.4)
8.2.5 Wood fiber cover board provides good adhesion surface for solvent-based and water-based membrane adhesives but is susceptible to moisture damage if the roof system is breached, and shall not be used in high-humidity or coastal environments without manufacturer confirmation of suitability.
8.2.6 Where PVC membrane is used, all insulation and cover board products shall be confirmed by the manufacturer to be resistant to plasticizer migration from the PVC membrane.
8.2.7 Polyiso insulation facers that contain bituminous materials shall not be used in direct contact with PVC membrane because plasticizer migration from PVC into bitumen alters the PVC membrane's physical properties over time.
8.3 Tapered Insulation System
○ Not required — positive slope in structural framing
● Tapered insulation — manufacturer's design required (submit for review)
○ Tapered insulation with crickets at curbs and equipment supports
8.3.1 Where positive slope is achieved through tapered insulation, the tapered system shall be designed by the insulation manufacturer's technical services group based on the drain locations, roof geometry, and required minimum slope shown on the roof plan.
8.3.2 The tapered design drawings shall be submitted to the Architect for review before insulation is fabricated and delivered.
8.3.3 The minimum slope in the tapered field areas shall not be less than 1/4:12 at any point.
8.3.4 Crickets and saddles around curbs and equipment supports shall be incorporated into the tapered insulation design.
8.3.5 The Contractor shall not substitute insulation thicknesses from the approved tapered design without the manufacturer's re-analysis and the Designer of Record's approval.
9 Vapor Retarder
9.1 Design Requirement
NOTE A vapor retarder is not universally required; it is required when the insulation analysis shows that the dew point will occur within or below the insulation assembly under design conditions, creating a risk of condensation that would degrade insulation performance, corrode the deck, or damage interior finishes. (9.1.1)
NOTE Specifying a vapor retarder as a precautionary measure in a low-humidity building in a warm climate can be counterproductive if it traps any incidental moisture that enters the assembly from the exterior. (9.1.2)
● No — condensation analysis confirms not required
○ Yes — condensation analysis confirms required (specify type below)
9.1.3 The need for a vapor retarder beneath the roof insulation shall be established by a condensation analysis performed by the Designer of Record using the ASHRAE Handbook of Fundamentals dew-point or hygrothermal analysis method, based on the building's interior temperature and relative humidity design conditions and the climate zone's exterior conditions.
9.1.4 The Designer of Record shall make the vapor retarder determination explicitly.
NOTE High-humidity interior environments — food processing facilities, natatoriums, hospitals with high-humidity procedure spaces, laundries, and similar occupancies — almost always require a vapor retarder, whereas standard office, retail, and warehouse interiors in most US climate zones typically do not require one. (9.1.5)
9.2 Vapor Retarder Materials
NOTE Vapor retarder materials vary in permeance from Class I (0.1 perm or less, effectively vapor-impermeable) to Class II (0.1 to 1.0 perm, vapor retarder) to Class III (1.0 to 10 perm). (9.2.1)
○ Self-adhering polymer-modified bituminous sheet — Class I (≤0.1 perm)
○ Mechanically fastened glass-mat reinforced vapor retarder — Class I or II
○ Kraft-faced or film-faced polyiso facer — Class II (coordinate with insulation specification)
● No vapor retarder
9.2.2 Where a vapor retarder is required, it shall be installed directly over the structural deck, below the insulation.
9.2.3 The vapor retarder shall be compatible with the deck type, the adhesive or fastening method for the bottom insulation layer, and the overall FM-approved or engineered assembly.
9.2.4 The required permeance class shall be determined by the condensation analysis.
9.2.5 Where a self-adhering sheet vapor retarder is used, all seams and end laps shall be rolled to ensure full adhesion.
9.2.6 Penetrations through the vapor retarder shall be sealed with compatible flashing membrane or tape per the manufacturer's instructions before insulation is installed.
9.2.7 The vapor retarder shall be protected from foot traffic and UV exposure and shall not be left exposed during multi-day construction halts.
10 Attachment and Fastening
10.1 Attachment Method Selection
NOTE The three principal attachment methods — mechanically attached, fully adhered, and ballasted — each have distinct structural, thermal, and wind-performance characteristics. (10.1.1)
● Mechanically attached — fastener-and-plate rows at seams
○ Fully adhered — membrane bonded to cover board with adhesive
○ Ballasted — loose-laid membrane, ballast at minimum 10 lb/sf
○ Hybrid — mechanically attached field, adhered perimeter and flashings
10.1.2 The attachment method shall be selected based on the required FM wind-uplift classification, the deck type and fastener pull-out value, the building's wind exposure, and the Owner's long-term performance requirements.
10.1.3 The attachment method shall be confirmed as part of an FM-approved or tested assembly; mixing attachment methods within a field zone is not permitted without separate FM-listing confirmation.
10.2 Mechanically Attached Systems
NOTE In mechanically attached systems, the membrane is secured by rows of fasteners and round or bar-shaped plates installed through the membrane at seam overlaps and into the insulation and deck; the membrane spans between fastener rows without bonding to the substrate. (10.2.1)
NOTE This is the most common attachment method for new commercial construction because it is faster to install than a fully adhered system, requires no adhesive cure time, and allows significant drainage-slope tolerances. (10.2.2)
6 in o.c. (heavy wind exposure)
9 in o.c.
12 in o.c. (standard commercial)
18 in o.c.
Per drawings (deferred by default)
10.2.3 Fastener type, diameter, and embedment depth shall be selected from the FM-approved assembly and shall be appropriate for the deck type.
10.2.4 Fasteners in steel deck shall be self-drilling, self-tapping screws of the type and length included in the FM-approved assembly.
10.2.5 Fasteners in concrete or lightweight concrete shall be of the type confirmed by pull-out testing to achieve the minimum required value.
10.2.6 Fasteners in wood shall be annular-ring-shank roofing screws.
10.2.7 The fastener-and-plate spacing in the field zone, perimeter zone, and corner zone shall be as specified on the wind-zone attachment drawing.
10.2.8 The Contractor shall not omit fasteners, reduce spacing, or substitute a fastener of different type or length without a revised FM-approval or engineering confirmation.
10.2.9 Under no circumstances shall the spacing in the perimeter or corner zone be the same as the field-zone spacing.
10.2.10 Fastener plates shall be round (standard diameter per the FM-approved assembly, commonly 3 inches) or bar-type for wide seam applications.
10.2.11 Plates shall be of corrosion-resistant steel, properly seated flat on the membrane surface without tilting or tearing.
10.2.12 Plates installed tilted more than 5 degrees from horizontal shall be removed and replaced.
10.2.13 The membrane seam lap shall cover all fastener plates by a minimum of 1 inch plus the seam overlap width required for welding, and exposed plate edges after seaming shall be corrected.
10.3 Fully Adhered Systems
NOTE In fully adhered systems, the membrane is bonded to the cover board or substrate across its entire surface with solvent-based bonding adhesive, water-based bonding adhesive, or two-part spray adhesive. (10.3.1)
NOTE Full adhesion eliminates the "billowing" behavior of mechanically attached membranes under wind uplift, distributes uplift loads across the entire membrane area, and provides better resistance to wind-driven water infiltration at the membrane surface; fully adhered systems are required in many high-wind FM-approved assemblies and are preferred for buildings with reflective metal or glass facades where wind-induced membrane flapping would cause aesthetic or acoustic concerns. (10.3.2)
NOTE Rolling the membrane into wet adhesive traps solvents, while rolling it into fully dry adhesive produces a poor-quality bond. (10.3.3)
● Solvent-based bonding adhesive (low temperature performance; VOC restrictions may apply)
○ Water-based bonding adhesive (low VOC; temperature-sensitive; longer flash-off)
○ Two-part spray adhesive (rapid flash-off; requires spray equipment)
10.3.4 The Contractor shall follow the adhesive manufacturer's published application rate (typically stated in square feet per gallon for each component or combined).
10.3.5 The Contractor shall not apply adhesive below the manufacturer's minimum temperature, in high humidity, or onto a wet, frosted, or contaminated substrate.
10.3.6 Both the membrane and the substrate shall receive adhesive (two-sided application) unless the specific adhesive is formulated for single-sided application.
10.3.7 Adhesive shall be allowed to flash off (become "tacky dry" — not wet, not fully dry) before the membrane is rolled in.
10.3.8 The Contractor shall use a hand probe or touch test to confirm flash-off condition immediately before rolling.
10.3.9 A membrane section rolled into adhesive at incorrect flash-off shall be documented, and if the bond is suspect it shall be probed with a seam probe tool and any unbonded areas remediated.
10.4 Ballasted Systems
NOTE In ballasted systems, the insulation and membrane are loose-laid over the deck and held in place entirely by the weight of smooth river-washed stone (typically 3/4-inch to 1-1/2-inch gradation) or concrete pavers. (10.4.1)
NOTE Ballasted systems are among the oldest single-ply attachment methods and are simple to install, but they impose significant dead load on the structure (typically 10 to 15 psf for stone ballast). (10.4.2)
○ Smooth river-washed stone, 3/4–1-1/2 in gradation, minimum 10 psf
○ Smooth river-washed stone, 3/4–1-1/2 in gradation, minimum 12 psf (high wind)
○ Concrete pavers, minimum 18 psf
● Not applicable — mechanically attached or adhered system
10.4.4 Ballasted systems shall not be used in high-wind-exposure zones without FM approval confirmation.
10.4.5 Because the FM-approved assembly accounts for ballast density and gradation, the ballast material used in the field shall match the specification in the FM-approved assembly.
10.4.6 Substituting crushed stone, slag, or pea gravel for smooth river-washed stone without FM-approval confirmation is not permitted.
10.4.7 The structural engineer shall confirm the ballasted system dead load is within the allowable capacity of the deck and framing system before installation.
10.4.8 The roofing Contractor shall notify the Structural Engineer of Record in writing if the specified ballast loading differs from the structural design loading.
10.5 Insulation Fastening
NOTE In steel decks, the minimum embedment is typically the full depth of the deck flute plus a minimum of 3/4 inch into the flange (i.e., the fastener reaches through the deck). (10.5.1)
NOTE Under-application of ribbon adhesive is a common field deficiency that reduces the uplift capacity of the assembly. (10.5.2)
● Mechanical fasteners and plates (insulation screws and discs)
○ Low-rise urethane or polyurethane foam adhesive ribbons
○ Full-coverage insulation adhesive
○ Per FM-approved assembly — combination of fasteners and adhesive
10.5.3 Regardless of the membrane attachment method, the insulation layers shall be mechanically fastened to the deck or adhered with insulation adhesive in a pattern that provides the required FM wind-uplift resistance.
10.5.4 Insulation boards shall not be loose-laid under a membrane that is subsequently mechanically attached or adhered to the cover board.
10.5.5 Insulation adhesive shall be applied in ribbons or full coverage as required by the FM-approved assembly.
10.5.6 Ribbon adhesive patterns shall be the correct bead width, spacing, and number of beads per board as listed.
10.5.7 The Contractor shall submit the specific adhesive pattern proposed for review as part of the submittal package.
10.5.8 Mechanical fasteners through insulation into the deck shall penetrate the structural deck by the minimum embedment required for the FM-approved pull-out value.
10.5.9 Fastener length shall account for all insulation thickness, cover board thickness, and deck geometry, and the Contractor shall calculate and verify fastener length before installation begins.
11 Flashings and Terminations
11.1 General Flashing Requirements
NOTE Flashings are the highest-risk elements in any membrane roofing assembly. (11.1.1)
NOTE The overwhelming majority of membrane roof failures that produce interior leaks originate at flashings, not at field seams: the field seam is a factory-controlled or welder-controlled straight-line joint, whereas the flashing is a three-dimensional, field-fabricated transition between the plane of the roof membrane and a vertical surface, a penetration, a curb, or a drain. (11.1.2)
NOTE Every change in plane requires flashing, and every flashing requires careful design and execution. (11.1.3)
● 8 in (minimum)
○ 12 in (preferred; high-snow or high-debris environments)
Per drawings — roof drawings
● 45-degree cant, minimum 3 in per face (standard)
○ Tapered edge strip — per FM-approved assembly
○ No cant (not recommended; requires documentation of alternative)
11.1.4 All membrane flashings shall be the same material as the field membrane or a manufacturer-approved compatible flashing membrane.
11.1.5 In TPO systems, flashings shall be TPO membrane or prefabricated TPO flashing components and shall be heat-welded to the field membrane, with no adhesive or tape terminations permitted at the seam between the field membrane and the flashing.
11.1.6 In PVC systems, flashings shall be PVC membrane welded to the field membrane.
11.1.7 In EPDM systems, flashings shall be EPDM membrane bonded with lap tape and primer, and may also use prefabricated EPDM flashing components (pre-molded corners, pipe boots) adhered with EPDM bonding adhesive.
11.1.8 Flashing membrane shall extend a minimum of 8 inches above the finished roof membrane surface on all vertical surfaces.
11.1.9 Where parapets, curbs, and walls are less than 8 inches tall, the Designer of Record shall evaluate an alternative detail (through-wall flashing, continuous cant with extended membrane height, or relocation of the base flashing height).
NOTE Eight inches is a widely accepted industry minimum that provides a safety margin against water infiltration from debris damming or localized ponding at the base of vertical surfaces. (11.1.10)
11.1.11 All vertical flashing surfaces shall have a cant strip or a tapered edge strip at the transition from horizontal to vertical to avoid an abrupt 90-degree bend in the membrane.
NOTE A 45-degree cant, minimum 3 inches per face, is standard practice and reduces membrane stress at the corner and provides a gentler transition that is less prone to membrane bridging and cracking. (11.1.12)
11.2 Wall and Parapet Flashings
NOTE Installing a termination bar on a horizontal surface creates a hydrostatic condition where water pools against the bar and is directed under the membrane; this is among the most common termination-bar installation errors. (11.2.1)
● Aluminum bar, minimum 1/8 in thick
○ Stainless steel bar, minimum 1/8 in thick (corrosive environments)
○ 6 in o.c. maximum (high wind or loose membrane)
● 12 in o.c. maximum (standard)
11.2.2 At concrete masonry unit, concrete, and structural steel walls, the membrane flashing shall be bonded to the vertical surface with membrane-compatible adhesive and terminated at the top with a metal termination bar.
11.2.3 Termination bars shall be continuous aluminum or stainless steel angle, minimum 1/8-inch thick, fastened through the membrane into the wall at maximum 12-inch on-center spacing and at maximum 6 inches from each end.
11.2.4 Lap sealant shall be applied over the top edge of the termination bar and into the fastener holes as a secondary barrier.
11.2.5 Termination bars shall be installed on vertical surfaces only.
11.2.6 On roofs with parapets, the termination bar shall be on the vertical face of the parapet, and the top of the parapet shall be covered by the coping cap system, which is a separate assembly from the membrane flashing.
11.2.7 At wood-framed or gypsum-sheathed walls, the membrane flashing shall be adhered to the sheathing and the top of the membrane shall be mechanically fastened with a termination bar before the wall cladding is applied.
11.2.8 The wall cladding shall lap over the top of the membrane flashing by at least 2 inches to prevent water from running behind the membrane at the top termination.
11.3 Roof Drains
● Formed sump in insulation, minimum 12 in radius, minimum 1 in deep
○ Prefabricated drain sump — match to drain body manufacturer
11.3.1 Membrane-roofing-compatible drain bodies shall be cast iron, cast aluminum, or thermoplastic, with a clamping ring that compresses the membrane between the drain body and the clamping ring to form the primary seal.
11.3.2 The drain body flange shall extend a minimum of 8 inches from the drain center, providing adequate surface area for the membrane-to-drain bond.
11.3.3 The membrane shall be bonded to the drain flange with adhesive appropriate for the membrane type.
11.3.4 The clamping ring shall be tightened evenly to the manufacturer's specified torque to create uniform compression without cutting the membrane.
11.3.5 Drain sumps shall be provided at all interior roof drains to create a recessed collecting area that allows drainage at lower effective water depth than a flat-mounted drain.
11.3.6 Drain sumps shall be formed in the insulation around each drain, with the sump extending at least 12 inches from the drain center and providing a minimum 1-inch depth below the adjacent finished insulation surface.
11.3.7 Overflow drains or overflow scuppers are required by IBC Section 1503.4 for all roofs where the primary drainage system could be blocked.
11.3.8 The overflow system shall be designed by the Designer of Record to handle the 100-year storm event.
11.3.9 Overflow drain openings shall be located 2 inches above the high point of the primary drainage system so that overflow drains activate only when primary drains are blocked.
11.3.10 Overflow scuppers shall penetrate the parapet wall and shall be detailed with membrane flashings that prevent water from entering the roof assembly through the scupper opening.
11.4 Penetration Flashings
NOTE Prefabricated boots are preferred because they are formed consistently, whereas field-fabricated flashings are prone to wrinkles, bridging, and inconsistent seam quality. (11.4.1)
● Prefabricated pipe boot — membrane-compatible (preferred)
○ Field-fabricated membrane boot — for non-standard pipe diameters
○ Pitch pocket — only for complex or clustered penetrations
11.4.2 Every penetration through the roof membrane — pipe, conduit, duct, equipment support, structural post — shall be flashed with a manufacturer-supplied or fabricated flashing that isolates the membrane from the penetration and provides a watertight seal.
11.4.3 The flashing shall accommodate the thermal movement, vibration, and differential settlement between the penetration and the membrane without tearing or debonding.
11.4.4 Pipe penetrations shall be flashed with prefabricated pipe boots or field-fabricated conical flashings.
11.4.5 All prefabricated boots shall be heat-welded (TPO, PVC) or adhered with tape and primer (EPDM) to the field membrane.
11.4.6 Multiple pipes in close proximity shall be individually flashed; grouping multiple pipes into a single pitch pocket or single oversized flashing is not acceptable.
11.4.7 The use of pitch pockets shall be minimized because they require periodic maintenance refilling as the sealant ages, shrinks, and weathers.
11.4.8 Where pitch pockets are used, they shall be fabricated from the same material as the field membrane (TPO, PVC) or from metal compatible with the membrane system, sealed with a semi-rigid two-part polyurethane sealant, and sloped to drain.
11.4.9 The Contractor shall identify all pitch pockets on the as-installed drawing for the Owner's maintenance reference.
11.5 Equipment Curbs and Supports
NOTE Point loads that indent or compress the insulation beneath the membrane without adequate distribution reduce thermal performance and can create stress concentrations in the membrane that lead to cracking. (11.5.1)
11.5.2 Equipment curbs — roof curbs for HVAC units, exhaust fans, skylights, and similar equipment — shall be minimum 8 inches in height above the finished membrane surface, rigid, and capable of supporting the equipment without differential settlement.
11.5.3 Curbs shall be pre-fabricated steel or factory-engineered wood; field-fabricated wood curbs shall not be used on NDL warranty projects.
11.5.4 The membrane shall be wrapped up and over the curb top and clamped under the equipment base frame, with a hook strip or clamping bar at the top of the curb to secure the membrane without puncturing it.
11.5.5 Blocking and equipment supports that bear directly on the membrane shall use membrane-compatible walkway or pressure-distribution pads.
11.5.6 Point loads from support legs that are not distributed by pads sufficient to keep contact pressure below the membrane manufacturer's published limit shall not be used.
12.1 Coping Caps
NOTE Coping caps cover the top of parapet walls and protect both the roofing membrane termination on the inside face of the parapet and the wall construction from water infiltration from above. (12.1.1)
NOTE A typical aluminum coping cap can expand approximately 1/8 inch per 10-foot panel for a 100°F temperature swing. (12.1.2)
● Aluminum, minimum 0.050 in (18 ga) thickness
○ Galvanized steel, minimum 24 ga (G90 coating)
○ Stainless steel, minimum 24 ga (coastal and corrosive environments)
○ Copper, minimum 20 oz per sq ft (historic and premium projects)
○ Mill finish (aluminum only)
● Factory painted — Kynar 500 or equivalent PVDF coating
○ Anodized
Per drawings
12.1.3 Coping cap design, material, gauge, and joint details shall conform to SMACNA Architectural Sheet Metal Manual and shall achieve the ANSI/SPRI ES-1 wind-pressure classification equal to or exceeding the design edge-zone pressure.
12.1.4 Coping caps that are not ES-1-tested for the design wind pressure shall not be installed; code compliance (IBC Section 1504.5) and FM Global requirements both mandate ES-1 compliance.
12.1.5 Coping cap joints shall include a standing seam or slip joint with sufficient thermal expansion allowance for the metal's anticipated temperature range and the cap span between joints.
12.1.6 Coping cap joints shall be detailed to accommodate thermal movement without stress.
NOTE Coping caps installed without expansion joints or with joints that are sealed rigid with caulk will buckle or crack in temperature extremes. (12.1.7)
12.2 Gravel Stops and Fasciae
NOTE At roof edges without parapets, a gravel stop or fascia edge metal system terminates the roofing assembly, provides a finished edge, and prevents wind from pulling the membrane back from the roof perimeter. (12.2.1)
12.2.2 At roof edges without parapets, a gravel stop or fascia edge metal system shall be installed to terminate the roofing assembly, provide a finished edge, and prevent wind from pulling the membrane back from the roof perimeter.
12.2.3 The edge metal system shall be ES-1-classified for the design edge wind pressure.
12.2.4 The membrane shall be sealed under the edge metal cleat or integrated hook strip; exposed membrane edges that are not mechanically clamped and sealed at the perimeter are a primary wind-uplift vulnerability.
12.3 Scuppers
12.3.1 Scuppers for overflow drainage or primary drainage through parapet walls shall be formed and flashed with the same membrane or compatible metal flashing material.
12.3.2 Scupper openings shall be cut cleanly through the parapet; ragged or uneven cuts shall be patched before flashing is applied.
12.3.3 Scupper flashings shall extend a minimum of 6 inches onto the roof membrane on all sides of the scupper opening and shall be fully bonded.
12.3.4 Metal scupper liners, where used, shall be set in membrane-compatible sealant and the membrane flashing shall be bonded over the liner flanges.
13 Installation
13.1 Membrane Layout and Seaming
NOTE Orienting seams parallel to slope prevents cross-slope seams that could collect water; T-joints — the intersection of a field seam with an end lap — represent a three-layer condition that requires special attention in both thermoplastic and EPDM systems. (13.1.1)
13.1.2 Membrane panels shall be laid out before seaming so that seams are oriented parallel to the roof slope direction (perpendicular to the eave or perimeter) wherever practicable.
13.1.3 End laps (seams perpendicular to the length of the roll) shall be staggered a minimum of 12 inches from adjacent end laps.
13.2 TPO and PVC Seam Welding
NOTE Properly welded seams fail in the membrane body, not at the weld interface; clean interface separation indicates insufficient weld temperature, speed, or pressure. (13.2.1)
● 1-1/2 in welded width (automatic welder)
○ 1 in welded width (hand welder)
13.2.2 All TPO and PVC field seams and flashing seams shall be made by hot-air welding with automatic or hand-welding equipment.
13.2.3 The seam overlap shall be a minimum of 1-1/2 inches of welded width for automatic welders and 1 inch for hand welders, measured after welding.
13.2.4 The weld shall be continuous and shall be probed with a rounded seam probe (cotter pin test) after welding and cooling, and the probe shall not be able to enter the weld without tearing the membrane.
13.2.5 Any location where the probe penetrates the seam is a void that shall be remediated by cleaning, priming, and re-welding.
13.2.6 Hot-air welder temperature and speed settings shall be verified at the start of each day and whenever conditions change (ambient temperature, wind, membrane temperature) by welding sample strips and performing peel tests.
13.2.7 Where peel-test seams separate cleanly at the interface without membrane tearing, the welder settings shall be adjusted before production welding resumes.
13.2.8 T-joints in TPO and PVC systems shall be treated with a three-corner patch of membrane welded over the intersection to cover the top layer's cut end and any gap that may exist at the three-way corner.
13.2.9 T-joint patches shall be rounded-corner or circular, minimum 4-inch radius, and shall be fully welded around the perimeter.
13.2.10 Untreated T-joints are a known leak source and shall not be left without a patch on any completed roof.
13.3 EPDM Seaming
NOTE EPDM seams do not develop their full strength instantaneously; full bond develops over 24 to 72 hours after seaming under moderate temperature conditions. (13.3.1)
13.3.2 EPDM seams shall be formed using lap tape and primer following the membrane manufacturer's published procedure.
13.3.3 The seam overlap shall be a minimum of 3 inches.
13.3.4 The membrane surface in the seam zone shall be cleaned with membrane cleaner or isopropyl alcohol, allowed to fully dry, and then primed with the manufacturer's splice primer.
13.3.5 Primer shall be allowed to dry to the manufacturer's specified condition before tape is applied.
13.3.6 Lap tape shall be rolled from one end of the seam to the other without lifting or repositioning to avoid trapping air under the tape.
13.3.7 The seam shall then be roll-pressed with a hand roller, working from the center of the overlap outward to remove air pockets.
13.3.8 Seam areas shall be protected from foot traffic, water, and membrane strain for a minimum of 24 hours after seaming.
13.3.9 EPDM T-joints shall be patched with a minimum 6-inch square patch of membrane applied with lap adhesive and primer, not lap tape, for dimensional stability at the three-way corner.
13.3.10 Field-cut EPDM edges that are exposed (not covered by a seam lap or patch) shall be treated with edge sealant to prevent peel-back initiation.
13.4 Flashing Installation Sequence
NOTE The correct sequence prevents the field membrane installation crew from working across incomplete flashings and ensures that partially installed roofs can shed water (even incompletely) during construction rain events. (13.4.1)
13.4.2 Flashings shall be installed in a sequence that ensures all horizontal-to-vertical transitions are complete and watertight before the field membrane installation proceeds in adjacent areas.
13.4.3 Base flashings at walls shall be in place before the adjacent field membrane is welded to them; installing the field membrane first and then applying flashings on top results in exposed field membrane edges at the base flashing intersection and is not acceptable.
13.5 Walkway Pads
NOTE Walkway pads protect the membrane from foot traffic and provide slip resistance in wet conditions. (13.5.1)
● Heat-welded to field membrane (TPO, PVC systems)
○ Bonded with manufacturer-approved adhesive (EPDM systems)
13.5.2 Membrane walkway pads shall be installed at all roof access hatches, fixed ladders, rooftop mechanical equipment requiring routine maintenance access, and any other locations designated on the roof plan.
13.5.3 Walkway pads shall be the same membrane material as the field membrane (or a manufacturer-approved compatible material), a minimum of 45 mils thick, and heat-welded (TPO, PVC) or bonded with adhesive (EPDM) to the field membrane.
NOTE Loose-laid walkway pads are not acceptable because they lift, migrate, and trap water and debris beneath them. (13.5.4)
13.6 Protection of Completed Work
13.6.1 The Contractor shall protect all completed membrane work from damage by subsequent roofing operations and other trades.
13.6.2 Membrane surfaces shall not be used as work platforms without plywood protection boards laid over the membrane.
13.6.3 No direct concentrated loads shall be placed on the membrane from equipment, pallets, or stored material without adequate load distribution.
13.6.4 Torches, hot equipment, or grinding operations shall not be performed on or adjacent to the installed membrane without a fire watch and protective heat-shielding board.
13.6.5 The membrane shall be protected from rooftop traffic during the critical initial cure and seam-set period (24 hours for EPDM, immediate for welded TPO and PVC).
13.6.6 Completed work that is damaged by other trades shall be reported by the Contractor and repaired before the roof is covered or ballasted.
13.6.7 All repairs shall be documented and included in the as-installed drawing with their locations marked for warranty reference.
14 Testing and Inspection
14.1 Seam Probe Test
14.1.1 All seams in thermoplastic (TPO, PVC) membrane systems shall be probed with a rounded-tip seam probe (cotter pin test) after the seam has cooled.
14.1.2 The probe shall be run continuously along the seam at every accessible seam within the day's production.
14.1.3 Any seam void — a location where the probe enters the seam without tearing the membrane — shall be circled with chalk and documented.
14.1.4 Seam voids shall be cut out (using a hot knife or by slitting to clean membrane) and re-welded within the same work day where feasible.
14.1.5 Seam voids left overnight shall be temporarily sealed with compatible tape before end of day.
14.1.6 Seam probe testing shall be performed by the seaming operator after each seam cools and by the roofing foreman on a minimum 10 percent spot-check of all seams.
14.1.7 Discrepancies between the operator's and foreman's tests shall be reviewed with the manufacturer's technical representative.
14.2 Flood Testing
NOTE ELD using low-voltage or high-voltage methods can detect defects in the membrane that are not visible during visual inspection; ELD is particularly effective over adhered membranes and over membranes installed over conductive cover boards, while its effectiveness over ballasted systems is limited. (14.2.1)
○ Flood test — 2 in depth minimum, 24 hours, confirm structural capacity first
● Electronic leak detection (ELD) — low-voltage vector mapping method
○ Visual inspection only — minimum for basic warranty; not recommended for NDL
○ Flood test at critical areas + ELD at field
14.2.2 At the Architect's or Owner's direction, or as required by the membrane manufacturer for NDL warranty issuance, flood testing shall be performed by temporarily blocking all drains and flooding the membrane surface with a minimum 2-inch depth of water for a minimum of 24 hours.
14.2.3 The deck below shall be inspected for leaks during the flood.
14.2.4 After testing, drains shall be unblocked and the roof shall be allowed to drain completely.
14.2.5 Flood testing shall not be performed on decks or structures that are not designed for the water load imposed, and the structural engineer shall confirm the allowable load before flood testing is requested.
14.2.6 Where flood testing is impractical due to structural limits, drain locations, or large roof areas, electronic leak detection (ELD) shall be used as an alternative or supplement.
14.3 Core Cuts and Substrate Inspection
14.3.1 The Architect or Owner's representative may require core cuts — removal of membrane, cover board, and insulation samples at representative locations — to verify that the installed assembly matches the approved submittal and that the substrate is dry and undamaged.
14.3.2 Core cuts shall be taken at a minimum frequency of one per 10,000 square feet of roof area for NDL warranty projects, or at a frequency directed by the Architect.
14.3.3 All core cut locations shall be patched immediately after cutting using the same membrane material and a full-width patch welded or bonded over the opening.
14.3.4 Core cut patch locations shall be marked on the as-installed drawing.
14.3.5 Core cuts that reveal wet, degraded, or missing insulation layers, mismatched fastener patterns, or any condition that does not match the approved submittal shall be cause for additional investigation, and the Contractor shall not proceed with additional installation until the discrepancy is resolved.
14.4 Final Inspection
14.4.1 A final inspection of the completed roofing system shall be performed in the presence of the Contractor, the membrane manufacturer's technical representative, and the Architect or Owner's representative.
14.4.2 The final inspection shall verify that all seams are probed and documented; all flashings are complete, bonded, and terminated; all penetrations are flashed; all edge metal is installed, sealed, and ES-1-compliant; all walkway pads are bonded; drains are unobstructed and functional; and no membrane is left exposed without termination.
14.4.3 The manufacturer's technical representative shall issue a written inspection report documenting any deficiencies requiring correction before warranty issuance.
14.4.4 The Contractor shall correct all deficiencies identified in the final inspection and shall notify the Architect and manufacturer's representative when corrections are complete.
14.4.5 A follow-up inspection shall be performed to confirm that all deficiencies are resolved before warranty documentation is executed.
15 Warranty
15.1 Contractor's Installation Warranty
NOTE This warranty is in addition to, and does not substitute for, the membrane manufacturer's warranty. (15.1.1)
2 years from substantial completion (minimum)
5 years from substantial completion
15.1.2 The Contractor shall provide a written warranty against defects in workmanship and against leaks attributable to the installation for a minimum of two years from the date of substantial completion.
15.1.3 The warranty shall cover the labor and materials required to repair any installation defect.
15.2 Membrane Manufacturer's Warranty
15.2.1 Two warranty types are available and shall be specified.
NOTE A **standard (dollar-limit) warranty** covers the cost of membrane materials only, subject to a prorated declining cap based on the remaining warranty term, and provides limited protection against major failures late in the warranty term. (15.2.2)
NOTE A **No Dollar Limit (NDL) warranty** covers the full cost of repairing qualifying leaks — labor and materials, without a monetary cap — for the warranty term, and requires an authorized contractor, a manufacturer inspection before issuance, and typically a higher-performance installation (greater thickness, additional flashing detail requirements, or minimum drain sump conditions). (15.2.3)
NOTE The elimination of the dollar cap eliminates the risk of a large mid-warranty repair bill. (15.2.4)
● NDL (No Dollar Limit) warranty — full labor and materials, no cap
○ Standard (dollar-limit) warranty — prorated materials only
10 years
15 years
20 years
25 years
30 years
☑ Membrane and membrane-manufacturer-supplied seam materials
☐ Cover board (where included in manufacturer assembly warranty)
☐ Insulation (where included in manufacturer assembly warranty)
☐ Flashing and penetration components (manufacturer-supplied)
☐ Edge metal (where included in manufacturer warranty extension program)
15.2.5 The membrane manufacturer shall provide a written warranty against defects in materials and workmanship, installed by an authorized contractor, for the specified warranty term.
NOTE NDL warranties are strongly recommended for new construction and for re-roofing projects where the Owner will carry the building for the full warranty term. (15.2.6)
15.2.7 The Contractor shall confirm NDL warranty eligibility conditions with the specific manufacturer before submittal.
15.2.8 The Contractor shall identify any project condition that may affect NDL warranty eligibility at the time of submittal, not after installation is complete.
NOTE NDL warranty eligibility typically requires authorized installer status; minimum membrane thickness (often 60 mil minimum for NDL, with 80 mil required for extended terms); specified flashing and penetration details from the manufacturer's published NDL detail set; a manufacturer pre-warranty inspection; and, in some programs, a minimum number of primary and overflow drains above a density threshold. (15.2.9)
15.2.10 Warranty coverage shall include the membrane and all manufacturer-supplied accessories and seam materials; the cover board and insulation layers where included in the manufacturer's assembly warranty; and flashings and penetration boots installed with manufacturer-supplied products.
15.2.11 Warranty exclusions (typically damage from traffic, abuse, unauthorized modifications, chemical exposure from HVAC discharge, and acts of nature) shall be disclosed to the Owner at the time of contract so that the Owner can establish appropriate maintenance protocols and rooftop access controls.
15.3 Common Warranty Voiding Conditions
15.3.1 The Owner shall be informed of the following conditions that typically void or limit the membrane manufacturer's warranty, so that appropriate operational controls can be established.
15.3.2 Rooftop equipment installation or modifications by other contractors after roof completion, without membrane manufacturer authorization, voids warranty coverage in the area disturbed.
15.3.3 The mechanical engineer shall locate and route equipment discharge to drains, not to the membrane surface, because HVAC condensate or equipment exhaust discharge directly onto the membrane without proper splash pads and routing produces accelerated degradation.
15.3.4 Chemical exposure from improper storage, spills, or process emissions shall be avoided, and the specific membrane type's chemical resistance shall be confirmed before the roof is used to store or vent chemicals.
16 Common Errors and RFI Generators
NOTE Low-slope membrane roofing generates a consistent set of field RFIs and installation errors. (16.1)
NOTE The following are among the most frequently encountered and are highlighted here so that the Contractor can take proactive steps to avoid them. (16.2)
16.3 Termination Bar on Horizontal Surfaces
NOTE Termination bars are designed for vertical application. (16.3.1)
NOTE Installing a termination bar on a horizontal surface — for example, flat on a parapet cap or on a horizontal ledge — creates a water dam that directs water behind the membrane rather than shedding it. (16.3.2)
NOTE All termination bars belong on vertical surfaces with sealant applied to both the top edge of the bar and into the fastener holes. (16.3.3)
16.4 T-Joint Voids in Thermoplastic Systems
NOTE The three-way intersection of two seams in TPO and PVC systems is a geometry challenge because the cut end of the top membrane layer creates a potential void or sharp edge transition. (16.4.1)
NOTE Every T-joint requires a rounded patch, minimum 4-inch radius, fully welded over the intersection. (16.4.2)
NOTE Projects that omit T-joint patching routinely develop leaks at those locations within two to five years. (16.4.3)
16.5 Insufficient Flashing Height
NOTE Base flashings installed at less than 8 inches above the finished membrane surface will be periodically submerged in debris-dammed or ponded water, particularly at parapet bases and around equipment curbs. (16.5.1)
16.5.2 The 8-inch minimum is a code and industry standard, and all flashings should be measured before concealment.
16.6 Fastener Over-Drive
NOTE Over-driven fasteners in mechanically attached systems tear through the fastener plate and no longer provide the design pull-out resistance. (16.6.1)
NOTE Fasteners belong driven to the point that the plate is firmly seated without indenting the membrane or pushing the plate into the insulation. (16.6.2)
16.6.3 Power tools belong set at a torque limit, and hand-driving with a screw gun should be checked against a test pull or torque gauge at the start of each day.
NOTE PVC membrane in contact with bituminous adhesives, bituminous vapor retarders, or coal-tar-based products will suffer plasticizer migration and degradation. (16.7.1)
16.7.2 All products in the assembly below a PVC membrane must be confirmed by the manufacturer as PVC-compatible.
16.8 Incomplete Adhesive Flash-Off in Fully Adhered Systems
NOTE Rolling fully adhered membrane into adhesive that is still wet traps solvents and produces an inconsistent, low-strength bond that will allow the membrane to lift under wind uplift. (16.8.1)
16.8.2 The flash-off condition must be verified before roll-in; adhesive that has dried too far produces equally poor bond.
NOTE Field mock-ups and daily calibration of flash-off timing are essential on fully adhered projects. (16.8.3)
16.9 EPDM Shrinkage at Flashings
NOTE EPDM has a coefficient of thermal expansion that produces meaningful dimensional change over the temperature range of a roof surface. (16.9.1)
NOTE On poorly adhered or ballasted EPDM systems, the membrane can shrink sufficiently over time to pull base flashings away from vertical surfaces, creating open gaps at the base flashing termination. (16.9.2)
NOTE All EPDM base flashings belong fully adhered to the vertical surface and properly terminated at the top. (16.9.3)
NOTE EPDM shrinkage is also a reason why the minimum flashing overlap onto the field membrane at base flashings is at least 6 inches — a shorter overlap can be pulled completely free by shrinkage. (16.9.4)
16.10 Insufficient Scupper Sizing
NOTE Overflow scuppers that are undersized for the drainage tributary area will not adequately relieve flood loading from the primary drain blocking during a design storm, exposing the structure to loads not included in the structural design. (16.10.1)
NOTE Scupper sizing is the Designer of Record's responsibility but is frequently an RFI item during construction because the indicated size conflicts with the parapet depth or the drain piping. (16.10.2)
16.10.3 Overflow drainage sizing should be confirmed by the Designer of Record before construction documents are issued.
16.11 Mismatched Insulation and Adhesive in PVC Systems
NOTE Multiple field cases have documented PVC failure where a non-PVC-compatible polyiso facer was used beneath a fully adhered PVC membrane. (16.11.1)
NOTE The plasticizer from the PVC migrates into the bituminous facer, stiffening the membrane, causing brittleness, and ultimately cracking. (16.11.2)
16.11.3 Material compatibility confirmation between the membrane, adhesive, and cover board is a required submittal item and must be documented before installation begins.