This standard governs the selection, specification, and installation of thermal insulation in the building envelope for buildings constructed under the International Building Code (IBC), International Energy Conservation Code (IECC), or ASHRAE 90.1 energy standard. It applies to new construction and to alterations that affect the thermal performance of existing assemblies. The standard addresses the full range of insulation materials used in commercial and residential building envelope assemblies, the verification of thermal performance, fire and smoke classification, moisture management through vapor retarder and air barrier coordination, installation quality grading, and the inspection and testing required to confirm that specified performance is actually achieved in the field.
Thermal insulation is one of the most cost-effective energy conservation measures in a building. However, its in-place thermal performance depends not only on the material's rated R-value but on how it is installed — whether cavities are completely and uniformly filled, whether thermal bridges are properly broken, whether vapor control is correctly placed, and whether the assembly remains dry over its service life. A well-specified insulation scope that is poorly installed may achieve only 50 to 70 percent of its design R-value. This standard therefore addresses both material requirements and installation requirements with equal rigor.
The building envelope is also the primary line of defense against moisture accumulation within the building structure. Incorrect placement of vapor retarders, mismatched permeance between assembly layers, and gaps in the air barrier all create conditions for condensation and long-term moisture damage. This standard coordinates insulation specification with the vapor retarder requirements of IBC Section 1405 and the air barrier requirements of IECC Section C402.5 and ASHRAE 90.1 Section 5.4.
Coordinate with Membrane Roofing for roof assemblies where insulation is specified as part of a single-ply, modified bitumen, or built-up roofing scope. Coordinate with Below Grade Waterproofing where insulation is installed on the exterior of below-grade foundation walls as protection board over waterproofing. Coordinate with Gypsum Board Assemblies for details at interior face of insulated wall assemblies. Coordinate with Hvac Ductwork for duct insulation within the building envelope. Coordinate with Fluid Applied Air Barrier where a separate fluid-applied air barrier membrane is used in conjunction with continuous insulation sheathing.
Equipment, materials, and installation shall comply with the latest adopted edition of the following standards and codes. Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record or Architect of Record directs otherwise in writing.
| Standard | Title |
|---|---|
| ASHRAE 90.1 | Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings |
| ICC IECC | International Energy Conservation Code |
| IBC Chapter 7 | Fire and Smoke Protection Features |
| IBC Chapter 14 | Exterior Walls (vapor retarder requirements) |
| IBC Section 2603 | Foam Plastic Insulation |
| ASTM C165 | Standard Test Method for Measuring Compressive Properties of Thermal Insulations |
| ASTM C177 | Standard Test Method for Steady-State Heat Flux and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus |
| ASTM C518 | Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus |
| ASTM C553 | Standard Specification for Mineral Fiber Blanket Thermal Insulation for Commercial and Industrial Applications |
| ASTM C578 | Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation |
| ASTM C612 | Standard Specification for Mineral Fiber Block and Board Thermal Insulation |
| ASTM C665 | Standard Specification for Mineral-Fiber Blanket Thermal Insulation for Light Frame Construction and Manufactured Housing |
| ASTM C1029 | Standard Specification for Spray-Applied Rigid Cellular Polyurethane Thermal Insulation |
| ASTM C1289 | Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board |
| ASTM C1320 | Standard Practice for Installation of Mineral Fiber Batt and Blanket Thermal Insulation for Light Frame Construction |
| ASTM C1338 | Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings |
| ASTM E84 | Standard Test Method for Surface Burning Characteristics of Building Materials |
| ASTM E96 | Standard Test Methods for Water Vapor Transmission of Materials |
| ASTM E283 | Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors |
| RESNET HERS | Residential Energy Services Network Home Energy Rating System Standards (for installation grading) |
| NFPA 285 | Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components |
| ICC 1100 | Standard for Spray-Applied Polyurethane Foam Plastic Insulation |
Contractor shall submit the following for the Architect's or Engineer's review prior to procurement and installation. Installation of insulation in any assembly shall not proceed until the corresponding submittals are reviewed and returned without rejection.
Contractor shall provide the following at substantial completion prior to final acceptance.
Insulation work shall be performed by installers experienced in the installation of the specific insulation type and assembly being executed. Spray-applied polyurethane foam (SPF) installation shall be performed by an applicator trained and certified by the foam system manufacturer, or by an applicator holding certification under a recognized SPF training program. A certified SPF applicator shall be on-site during all SPF application operations; SPF shall not be applied by untrained laborers.
Mineral fiber batt and blanket installation in assemblies subject to HERS rating or energy code documentation shall achieve RESNET Grade I installation in all conditioned-space assemblies unless the project energy model explicitly accounts for a lower installation grade in the HERS score or compliance calculation. Installation grade shall be verified by a HERS rater or a qualified third-party inspector before assemblies are closed.
Insulation shall be specified and installed to meet the minimum requirements of the energy code adopted by the Authority Having Jurisdiction. The Contractor shall treat the insulation scope as a regulated energy-code element, not merely a material supply item. Where the project uses a prescriptive compliance path under IECC or ASHRAE 90.1, minimum R-values by climate zone shall be met for each assembly type. Where the project uses a performance compliance path (energy modeling), the modeled assembly R-values shall be achievable with the specified materials and installation method.
The Contractor shall verify that no assembly is closed — drywalled over, covered by cladding, or membraned — before the insulation in that assembly has been inspected by the Authority Having Jurisdiction, the HERS rater, or the designated third-party inspector as required by the adopted energy code.
All insulation products shall be listed, labeled, and certified by the manufacturer as conforming to the applicable ASTM product standard. Labels shall be intact on delivered materials. The stated R-value on the label or product data sheet shall be based on tests conducted per ASTM C518 or C177 at the mean temperature relevant to the application (75°F mean temperature for most building envelope applications).
Polyisocyanurate board insulation shall be labeled with its Long-Term Thermal Resistance (LTTR) value per ASTM C1289, not its initial thermal resistance. Polyiso's thermal performance decreases over the first several years after manufacture as blowing agent gases diffuse out of the foam cells; LTTR represents the stabilized in-service value and is the appropriate basis for energy code compliance calculations.
The minimum R-values required by the adopted energy code (IECC or ASHRAE 90.1) are a function of climate zone, building type (residential or commercial), and assembly type (roof/ceiling, above-grade wall, below-grade wall, slab). The Contractor shall obtain the climate zone for the project location from the drawings or from the energy code report; the climate zone governs minimum R-values throughout this standard.
The prescriptive minimum R-values for the project climate zone shall be as tabulated on the energy compliance drawings or energy code compliance report. These values represent the minimum acceptable performance level; the Architect or Engineer may specify higher R-values for energy efficiency, owner goals, or resilience objectives.
The nominal R-value of an insulation product is the R-value of the insulation material alone. The assembly R-value is the thermal performance of the complete wall, roof, or floor section including framing members, air films, and all other materials. These are not the same. Framing members in stud walls and roof framing create thermal bridges that substantially reduce the assembly R-value below the cavity R-value. ASHRAE 90.1 Section 5.5 and the supporting tables are based on assembly R-values (opaque assemblies), not nominal cavity R-values.
For a typical wood-framed wall with 2×6 studs at 16 inches on center, the framing fraction reduces the effective clear-field R-19 cavity assembly to approximately R-15 to R-17 at the whole-wall level. This is why IECC and ASHRAE 90.1 increasingly require continuous insulation layers on the exterior of framed walls — to supplement the cavity insulation and reduce the influence of framing members on whole-assembly performance.
Design R-values for each assembly type shall be as indicated on the building envelope drawings and energy code compliance documentation. The following datasheet elements record the specified minimum R-values for submittal verification and field inspection documentation.
All insulation materials shall be new, undamaged, and free of moisture at time of installation. Materials that have been wetted, compressed, torn, or otherwise damaged in storage or handling shall be discarded and replaced. The Contractor shall store insulation materials in a dry, covered location, off the ground, and protected from exposure to weather, mechanical damage, and UV degradation until immediately before installation.
Mineral fiber batt and blanket insulation for light frame construction shall conform to ASTM C665. Mineral fiber blanket for commercial and industrial applications shall conform to ASTM C553. Mineral wool (rock wool or slag wool) board insulation shall conform to ASTM C612.
Mineral fiber includes glass fiber (fiberglass) and mineral wool (rock or slag wool) products. Mineral fiber is noncombustible per ASTM E136 and requires no thermal or ignition barrier when installed in noncombustible assemblies or when left exposed in unconditioned spaces such as attics. The noncombustibility of mineral fiber is one of its key advantages in fire-sensitive applications. Mineral wool board products offer higher compressive strength, greater dimensional stability at elevated temperature, and better moisture resistance compared to glass fiber batts, making them well-suited for continuous exterior insulation and under-slab applications.
Kraft-faced batts provide a Class II vapor retarder as part of the batt facing and are appropriate in climate zones where a Class II retarder is required at the warm-in-winter interior face. The kraft facing shall face the conditioned space side of the assembly in heating-dominated climates (zones 5–8). Foil-faced batts provide a Class I vapor retarder and shall be used with care; Class I retarders can trap moisture in mixed climates and are generally not recommended for above-grade walls in zones 1–4. Where facing material is also intended to serve as the vapor retarder, the specifier shall confirm that the facing's permeance is appropriate for the climate zone and assembly configuration.
Extruded polystyrene rigid board insulation shall conform to ASTM C578. XPS is produced by extruding molten polystyrene through a die, yielding a closed-cell foam with low water vapor permeance (typically 1.0 perm at 1-inch thickness), high compressive strength, and good moisture resistance. ASTM C578 classifies XPS into multiple types by compressive strength; the appropriate type shall be selected based on the structural loads to which the insulation will be subjected.
XPS delivers approximately R-5.0 per inch. Unlike polyiso, XPS's R-value per inch is relatively stable across a wide temperature range, which is an advantage in cold-climate below-grade and at-grade applications. The blowing agents used historically in XPS production had high global warming potential; many manufacturers have transitioned to lower-GWP blowing agents, and the specifier should confirm the product's blowing agent status where environmental criteria apply.
Expanded polystyrene rigid board insulation shall conform to ASTM C578 (EPS types). EPS is produced by expanding polystyrene beads in a mold; it has an open-cell micro-texture that allows water vapor to pass more freely than XPS, with permeance typically 2–5 perms at 1-inch thickness depending on density. EPS delivers approximately R-3.6 to R-4.2 per inch depending on density; higher-density EPS achieves higher R-value per inch and higher compressive strength.
EPS is dimensionally stable and does not shrink or expand significantly over time, making it well-suited for below-grade applications where long-term dimensional stability is important. It does not use blowing agents with significant global warming potential and retains most of its R-value over time, unlike polyiso at low temperatures. EPS is appropriate for below-grade walls, under-slab insulation, and as continuous exterior sheathing where its higher vapor permeance is acceptable or desirable for the assembly's moisture management strategy.
Polyisocyanurate board insulation shall conform to ASTM C1289. Polyiso delivers the highest R-value per inch of any commercially available rigid board insulation under standard test conditions (approximately R-6.5 per inch at 75°F mean temperature), making it the dominant insulation choice for low-slope commercial roofing and exterior continuous insulation in above-grade walls.
A critical characteristic of polyiso is its temperature-dependent thermal resistance. At mean temperatures below approximately 40°F, polyiso's R-value degrades substantially — by 20 to 35 percent depending on product and temperature. This degradation is reversible (performance returns at higher temperatures) but it means that polyiso specified solely on its 75°F test value may not deliver the expected winter performance in cold-climate continuous insulation applications. For climate zones 5–8, the specifier should either use LTTR values, account for thermal performance at cold conditions, or supplement polyiso with a layer of XPS or mineral wool that maintains performance at low temperatures.
ASTM C1289 classifies polyiso into types based on facing material. The most common facing for roofing applications is a glass fiber-reinforced felt or glass mat facer (Type I, Type II); for wall applications, foil-faced polyiso is commonly used and provides a Class I vapor retarder and radiant barrier. The facing determines the product's vapor permeance, fire performance classification, and suitability for specific adhesives and field cuts.
Spray-applied polyurethane foam insulation shall conform to ASTM C1029 for closed-cell SPF (ccSPF) and to ICC 1100 for open-cell SPF (ocSPF). SPF is applied as a two-component liquid system that expands and cures in place, filling complex geometries, bridging gaps, and adhering to the substrate. It is the only insulation type that simultaneously provides insulation and a continuous air barrier in a single material application, which is a significant installation advantage in complex assemblies with many penetrations and irregular framing.
Closed-cell SPF delivers approximately R-6.0 to R-7.0 per inch, has very low vapor permeance (less than 1.0 perm at 2 inches), high structural rigidity, and excellent moisture resistance. Closed-cell SPF applied at 2 inches meets the vapor retarder requirement of many climate zones as a Class II retarder. Open-cell SPF delivers approximately R-3.5 to R-3.8 per inch, has higher vapor permeance (greater than 10 perms), lower density, and lower cost per R-unit; it is not an adequate vapor retarder and is not moisture-resistant. Open-cell SPF shall not be used in roofing applications, on exterior surfaces exposed to weather, or in any location where its high vapor permeance would create a vapor or moisture management problem.
SPF application is critically dependent on substrate temperature, ambient temperature, humidity, mixing ratio, and applicator technique. The SPF manufacturer's minimum substrate temperature (typically 40°F) shall be met and maintained during application and cure. Application outside the manufacturer's environmental window shall not proceed and shall require written authorization from the SPF manufacturer.
SPF cores shall be taken in locations agreed upon with the Architect during the pre-application meeting, at a frequency of at least one core per 1,000 square feet of applied area, or as directed by the contract documents. Core locations shall be patched by the SPF installer immediately after sampling with the same SPF material.
All insulation materials installed in building envelope assemblies shall meet the fire and smoke classification required by the IBC for the specific assembly and occupancy. The Contractor shall confirm the applicable fire code requirement for each assembly before procurement and shall not substitute insulation products that alter the fire classification of a tested assembly.
Insulation materials required to demonstrate surface burning characteristics shall be tested per ASTM E84 (Steiner Tunnel test). ASTM E84 measures the Flame Spread Index (FSI) and the Smoke Developed Index (SDI) of the material surface. IBC Chapter 8 and Chapter 26 use these indices to classify interior finish and foam plastic insulation. The standard reporting convention is "FSI/SDI" (e.g., 25/450).
Mineral fiber (glass fiber and mineral wool) insulation products are noncombustible and are not subject to the ASTM E84 requirements imposed on foam plastic insulation. However, mineral fiber products with facings (kraft, foil, or composite) do require surface burning classification of the faced assembly if the facing is left exposed; unfaced mineral fiber in a concealed cavity does not require ASTM E84 documentation.
Foam plastic insulation installed in buildings regulated by the IBC is subject to IBC Section 2603. The key requirements are:
IBC Section 2603.3 requires that foam plastic insulation have a maximum FSI of 75 and maximum SDI of 450 per ASTM E84 in all applications except where the insulation is installed within a tested assembly.
IBC Section 2603.4 requires that foam plastic insulation be separated from all interior spaces by a thermal barrier of minimum 15-minute fire resistance, unless an exception in Section 2603.4.1 applies. The standard thermal barrier is 1/2-inch gypsum board. Exceptions include foam plastic within roofing systems, within HVAC plenums that are entirely enclosed by noncombustible materials, and specific listed assemblies.
IBC Section 2603.5 requires that exterior walls containing foam plastic insulation meet the fire propagation requirements of NFPA 285, which is a full-scale assembly fire test. NFPA 285 testing evaluates whether fire propagates vertically through the exterior wall assembly, including the foam insulation, any combustible drainage plane materials, and the exterior cladding. NFPA 285 must be satisfied for the entire assembly, not just the individual foam product. A product's ASTM E84 classification does not substitute for NFPA 285 assembly testing where NFPA 285 is required. The Contractor shall confirm that any exterior wall assembly containing foam plastic has a documented NFPA 285 test or qualifies for an exemption before procurement.
IBC Section 2603.9 (attics and crawl spaces) requires that foam plastic insulation within an attic or crawl space entered only for utility service be protected from ignition by a covering of 1-1/2-inch mineral fiber insulation, 1/4-inch wood structural panel or equivalent, 3/8-inch gypsum wallboard, or another approved ignition barrier material, unless the foam product has been specifically tested and listed as an ignition-barrier-exempt material.
Vapor retarders shall be classified by water vapor permeance as determined by ASTM E96 wet-cup or dry-cup method, as follows:
Class I vapor retarders have permeance of 0.1 perm or less. Examples: polyethylene sheet, aluminum foil, foil-faced polyiso facer. Class I retarders are highly restrictive and shall be used only where specified by the Architect, because they can trap moisture in assemblies that experience seasonal reversal of vapor drive.
Class II vapor retarders have permeance greater than 0.1 perm and at or below 1.0 perm. Examples: kraft-faced insulation facer, coated kraft paper, some low-permeance paints. Class II retarders are appropriate in cold-climate above-grade walls where vapor drive from inside to outside is dominant in winter.
Class III vapor retarders have permeance greater than 1.0 perm and at or below 10 perms. Examples: standard latex paint on gypsum board, house wrap materials in this range. Class III retarders are appropriate only in climate zones where adequate continuous insulation on the exterior prevents condensation within the wall cavity (per IBC Table 1405.3.3 ratios), shifting the dew point to the exterior side of the thermal envelope.
IBC Section 1405.3 and IRC Section R702.7 require vapor retarders as follows: Climate Zones 5, 6, 7, 8, and Marine 4 require a Class I or II vapor retarder on the interior (warm-in-winter) face of the frame wall insulation, unless the assembly includes sufficient continuous exterior insulation to keep the interior wall sheathing above the dew point. Climate Zones 1, 2, and 3 do not require a vapor retarder; in hot-humid climates, a vapor retarder on the interior face is actually counterproductive because it traps moisture driven inward by outdoor humidity. Climate Zone 4 (non-marine) requires a Class I, II, or III vapor retarder.
The minimum thickness of continuous insulation that allows a Class III vapor retarder (painted drywall) to be used in lieu of Class I or II varies by climate zone and wall R-value. These ratios are established in IBC Table 1405.3.3, which specifies the minimum ratio of exterior continuous insulation R-value to total wall R-value required to shift the dew point. The Contractor shall not substitute vapor retarder products without confirming compliance with the applicable IBC table and climate zone requirements.
The air barrier and the vapor retarder serve different functions and are not always the same material. The air barrier resists bulk air movement through the assembly; the vapor retarder controls diffusion of water vapor through the material. The air barrier should be continuous across the entire building envelope; the vapor retarder is placed at a specific layer within the assembly.
In SPF assemblies, closed-cell SPF serves simultaneously as insulation, vapor retarder, and air barrier in the locations where it is applied. In assemblies using batt cavity insulation with a separate house wrap air barrier on the exterior sheathing, the air barrier and vapor retarder are distinct layers. The Contractor shall confirm that no gap, penetration, or construction joint interrupts the continuity of either the air barrier layer or the vapor retarder layer.
Penetrations through the vapor retarder — for electrical boxes, pipes, and mechanical connections — shall be sealed with compatible materials per the vapor retarder manufacturer's instructions. Vapor retarder material that is cut, torn, or punctured during installation shall be repaired before the assembly is closed. Repairs shall lap at least 6 inches and be taped with a compatible tape specified by the vapor retarder manufacturer.
In low-slope roofing assemblies, a vapor retarder installed below the roof insulation prevents warm, humid interior air from reaching the cold insulation layer and condensing. This is critical in climate zones 5–8 and in buildings with high interior humidity (natatoriums, food processing facilities, commercial kitchens). Roofing vapor retarders are coordinated with the roofing membrane assembly and shall be specified in coordination with Membrane Roofing. This standard addresses only the insulation above the vapor retarder; the vapor retarder substrate material is governed by the roofing assembly standard.
Insulation shall be installed in accordance with the manufacturer's published installation instructions, ASTM C1320 for mineral fiber batt and blanket, and ICC 1100 for spray-applied polyurethane foam. Where the instructions conflict with this standard or the contract documents, the more stringent requirement shall apply.
All substrates receiving insulation shall be clean, dry, and within the manufacturer's specified temperature range. Substrates with visible moisture, frost, ice, or standing water shall not receive insulation until the moisture condition is corrected and the substrate is within the acceptable temperature range. Insulation shall not be installed over wet concrete, wet masonry, or wet structural sheathing.
Mineral fiber batt and blanket installed in stud-framed wall cavities shall fill the cavity completely from stud face to stud face and from bottom plate to top plate, without voids, gaps, or compression. Insulation shall be split around wiring, blocking, and other obstructions so that insulation fills both sides of the obstruction; the total installed thickness shall equal the cavity depth. This splitting and fitting practice is the most common Grade I requirement violated in the field — a single batt folded behind a wire rather than split yields a localized void that can reduce the effective R-value of that cavity section by 30 to 50 percent.
Where batts are installed in two-stud-bay increments, joints between adjacent batts shall be butted tightly without gaps. Batts at the top and bottom of the cavity shall be cut to length and fitted without fold-over or compression. Batt width shall match the stud spacing so the batt is friction-fit snugly.
In masonry cavity wall construction, mineral wool or glass fiber batt insulation installed in the cavity between the inner wythe and the outer masonry veneer shall be secured against sagging over the full height of the cavity by insulation clips, self-adhering insulation, or a continuous horizontal support at floor lines. Unsecured batts in tall masonry cavities settle over time, creating insulation-free zones at the top of each floor level that are significant thermal leaks.
Rigid board continuous insulation (XPS, EPS, polyiso, or mineral wool board) applied to the exterior face of the structural wall sheathing shall be installed in full-coverage courses with staggered joints in multiple layers and with all joints offset a minimum of 12 inches both horizontally and vertically. Joints shall not be through-aligned between layers, because aligned joints create a thermal stripe that significantly reduces the thermal benefit of the continuous insulation layer.
Board joints in continuous exterior insulation shall be taped with a compatible tape to minimize air infiltration at joints, unless the exterior air barrier is provided by a separate fluid-applied or sheet-applied layer outboard of the insulation. Where the taped rigid board joints are the primary air barrier, every joint shall be taped including field cuts, perimeter edges at windows, doors, and penetrations, and transitions to adjacent assemblies.
Window and door rough opening perimeters shall receive flexible flashing tape or sealant at the transition between the continuous insulation and the window or door assembly. This perimeter transition is one of the highest-frequency air leakage locations in the building envelope and shall be specifically detailed on the drawings and carefully executed in the field.
Polyisocyanurate or XPS board insulation in low-slope roofing assemblies shall be installed in accordance with the requirements of the roofing assembly, as governed by Membrane Roofing, and with the roofing manufacturer's published requirements for the insulation substrate. The insulation shall be installed in at least two layers for thicknesses above 2.5 inches total, with joints offset 12 inches minimum both in the plane of the roofing and between the two layers, so that no through-joint path exists. Through-aligned joints create visible ridges in the membrane and points of accelerated moisture accumulation.
Tapered insulation for positive slope drainage at low-slope roofs shall be installed per the tapered insulation layout drawing, which shall be provided by the tapered insulation system supplier and coordinated with the roofing assembly. The minimum required slope for drainage shall be 1/4 inch per foot unless the roofing system manufacturer approves a lesser slope. Insulation panels shall be installed sequentially following the drainage direction; random installation that disrupts the taper gradient shall not be permitted.
In attic assemblies, insulation may be installed either at the roof deck plane (unvented attic, insulation between and over rafters) or at the ceiling plane (vented attic, insulation over the top plate). Where the attic is vented, insulation shall be installed at the ceiling plane and shall not block the eave vents or ridge vents; baffles shall be installed at each rafter bay from the top-of-wall plate to at least 12 inches above the top of the insulation, maintaining a clear ventilation channel of minimum 1-inch depth.
Where blown-in or batt insulation is used in a vented attic, minimum installed depth shall be maintained uniformly across the entire ceiling area including above the top plates, at blocking and bridging, and in any knee-wall areas. Access hatches to the attic shall be insulated to match the ceiling R-value with rigid insulation, insulated hatch covers, or a combination; uninsulated attic hatches are a common but significant thermal bypass.
Insulation installed between floor joists over unconditioned crawl spaces or garages shall be friction-fit tightly against the subfloor and held securely in place by insulation supports (wire rods, netting, or strips) spaced at 18 inches on center maximum so that the insulation cannot sag or fall. Insulation that sags away from the subfloor creates a significant convective loop and may also create a habitat for pests. Where the floor insulation facing is a vapor retarder, the facing shall face toward the heated space (upward in a floor over a crawl space).
In conditioned crawl spaces where the insulation is installed on the crawl space walls rather than the floor joists, rigid board or closed-cell SPF shall be applied to the interior of the foundation wall from the sill plate down to the footing. The insulation shall extend from 24 inches below grade to the top of the footing and shall be protected from mechanical damage in accessible crawl spaces. Foundation wall insulation shall be detailed to prevent moisture wicking from the concrete into the insulation by using materials with adequate drainage capability or by detailing appropriate drainage planes.
Rigid insulation on the exterior of below-grade foundation walls shall be protected from physical damage above grade and from UV degradation at the grade line. Protection board (minimum 1/4-inch rigid board), dimple drainage mat, or concrete parging shall be applied over the rigid insulation from the top of the insulation down to 6 inches below grade at minimum. Above-grade exposure of XPS or polyiso foam plastic is not permitted; mineral wool board or specifically listed below-grade exterior products shall be used where the insulation will remain exposed above grade.
Under-slab insulation shall be rigid board (XPS, EPS, or mineral wool board) rated for the compressive loads imposed by the slab and contents. The minimum compressive resistance shall be 15 psi (EPS Type II, XPS Type XIII or higher) for residential-scale uniform floor loads; heavier commercial or warehouse loads shall require higher-compressive-strength products per the structural engineer's direction. Under-slab insulation shall be installed in continuous coverage without gaps; gaps at column footings, thickened slab edges, and pipe penetrations are common installation defects that create localized thermal short circuits.
Continuous insulation (ci) is insulation that extends across all structural members in the assembly without thermal bridges other than fasteners and service openings, as defined by ASHRAE 90.1. By eliminating the thermal bridge created by framing members, continuous insulation dramatically improves the whole-assembly R-value compared to cavity-only insulation of the same nominal value. The benefit of continuous insulation increases with framing fraction; metal-framed walls with continuous exterior insulation achieve whole-wall R-values that would be nearly impossible to approach with cavity insulation alone.
ASHRAE 90.1 prescriptive tables for above-grade walls in climate zones 3–8 require continuous insulation in combination with (or as an alternative to) cavity insulation. The specific minimum ci thickness and total R-value depend on the climate zone, the framing material (wood vs. metal stud), and the framing spacing. The project energy code compliance documentation shall identify the minimum ci R-value for each above-grade wall type.
Wood stud walls have a framing fraction of approximately 20–25 percent at 16 inches on center. The R-value of wood is approximately R-1.4 per inch, which is substantially lower than that of the cavity insulation it displaces. A 2×6 wood-framed wall with R-19 batts achieves a whole-wall effective R-value of approximately R-15 due to framing. Continuous exterior insulation of R-5 to R-7.5 brings the whole-wall assembly close to R-20 to R-22.
Metal stud walls have significantly more severe thermal bridging because steel has very high thermal conductivity — approximately 320 times that of wood. A metal-framed wall with R-19 batt insulation between studs achieves an effective whole-wall R-value of only approximately R-8 to R-10 due to thermal bridging through the steel studs, even though the nominal cavity R-value is R-19. Continuous exterior insulation is essential in metal-framed construction. The required ci R-value for metal stud walls is substantially higher than for comparable wood-framed walls to achieve the same whole-wall performance.
When rigid continuous insulation is fastened through by long structural screws to attach cladding or rain screen systems, each fastener penetrating the insulation is a thermal bridge. The magnitude of this thermal penalty depends on the fastener material (steel vs. nylon or stainless), fastener diameter, spacing, and the thickness of insulation penetrated. For ASHRAE 90.1 performance compliance, the thermal penalty of fasteners through continuous insulation shall be accounted for in the assembly U-factor calculation. Nylon-tipped or thermally broken fastening systems reduce this penalty and shall be used where drawings or specifications require it.
The most common field RFIs related to continuous insulation concern: (1) how to maintain CI continuity at window and door rough openings, which are inherently interrupted in the exterior insulation plane; (2) how to attach heavy cladding systems (brick, stone, precast) through multiple inches of compressible or crushable CI; (3) transitions at roof-wall intersections where CI must transition between wall and parapet insulation without interruption; and (4) penetrations for pipes, conduit, and HVAC equipment that puncture the continuous insulation layer.
Drawings shall detail each of these conditions before construction begins. Where drawings are silent, the Contractor shall submit an RFI and shall not close the insulation layer until a detailed resolution is documented. Improper field resolutions at CI transitions and penetrations are among the most significant thermal defect sources in modern construction.
Before insulation installation begins in each assembly area, the Contractor shall inspect and confirm the following: all framing is complete, plumb, and at the correct spacing; all rough mechanical, electrical, and plumbing work is installed and inspected; all substrate sheathing is fastened and any required air barrier membrane is applied; the substrate is dry and within the temperature range for the insulation product; and the insulation products on-site match the approved submittals.
Insulation installation shall be subject to in-progress inspection before assemblies are closed. In-progress inspection shall confirm that all cavities are uniformly filled without voids or compression (RESNET Grade I as required), that all batts are properly split around obstructions, that continuous insulation boards are in full contact with the substrate without gaps or hollow spots, that all taped CI board joints are fully adhered, and that vapor retarder facing and any separate vapor retarder membrane are intact and oriented correctly.
The Architect, Owner's designated inspector, or the HERS rater shall have the right to observe insulation installation at any time before assemblies are closed. The Contractor shall notify the designated inspector at least 48 hours before any insulation is scheduled to be concealed by finishes or cladding.
Where required by the adopted energy code (IECC Section R402.4 for residential or IECC Section C402.5 for commercial), air barrier continuity shall be verified by a whole-building pressurization test (blower door test) after the building envelope is complete and before insulation and finishes conceal the air barrier layer. The maximum allowable air leakage rate shall be per the adopted code and shall be as noted on the energy compliance drawings or energy code report.
Spray-applied polyurethane foam shall be verified for thickness and density by core sampling after application and before the foam is concealed. Cores shall be taken in the locations and at the frequency established in the pre-application meeting. Minimum acceptable thickness shall be the specified minimum minus 1/4 inch at any single core location. Minimum acceptable density shall be within the range specified by ASTM C1029 for the product type. Cores that do not meet minimum thickness or density requirements shall trigger additional cores in the surrounding area and remedial application as directed by the Architect.
Infrared thermographic scanning of the completed building envelope is a powerful tool for identifying insulation voids, thermal bridges, and air leakage pathways that are not visible by conventional inspection. Thermographic scanning requires a minimum temperature differential of 10°F between interior and exterior and shall be conducted during heating season in cold climates or cooling season in hot climates. Where infrared scanning is specified as a quality assurance measure, the Contractor shall provide access to the building interior and shall coordinate the timing with the Owner's or Architect's thermographer.
Insulation products carrying a manufacturer's material warranty against defects in materials shall be warranted to the Owner. The Contractor shall submit warranty documents as part of closeout submittals. Typical manufacturer warranties for rigid board insulation products are 10 to 25 years for resistance to physical degradation; the specific warranty coverage and exclusions vary by manufacturer and product, and the Contractor shall review the applicable warranty before procurement.
Spray-applied polyurethane foam systems typically carry a material warranty of 10 years from the system manufacturer when installed by a certified applicator in conformance with manufacturer requirements. Warranty coverage for SPF is often conditional on the foam being covered by a compatible protective coating or covered by finished materials; uncovered and UV-exposed SPF is not warranted and will physically degrade within 1–2 years of UV exposure.
The Contractor shall warrant the insulation installation against defects in workmanship, including voids, compression, improper facing orientation, unsealed joints, and failure to achieve specified R-value in completed assemblies, for the project warranty period from the date of substantial completion.
Where blower door testing reveals air leakage above the specified maximum during the warranty period, the Contractor shall identify and correct the leakage source and re-test at no additional cost to the Owner. Where thermal imaging reveals insulation voids or deficiencies during the warranty period, the Contractor shall open the affected assembly, correct the deficiency, and restore the assembly at no additional cost to the Owner, unless the deficiency is demonstrably due to post-completion Owner modifications.
The Contractor shall maintain and provide to the Owner at closeout a complete set of energy code compliance documentation, including the certificate of compliance, the energy code report, blower door test results, HERS rater inspection reports where applicable, and any other documentation required by the AHJ for energy code compliance certification. This documentation is required for certificate of occupancy in many jurisdictions and shall be treated as a contract deliverable.