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SynC · Editorial revision

Vapor Retarders

Revision5
EditedOct 12, 2026
StatusCurrent
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Current revision. This is editorial revision 5, the current text of this standard. Read it on the standard's page.

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1 Scope

NOTE This standard covers the dedicated vapor retarder installed within an above-grade framed or furred wall assembly, at the ceiling plane below a vented attic, or within a framed roof assembly with cavity insulation: the class the assembly requires, the side of the insulation the retarder occupies, the product that provides it, and the seams, penetrations, terminations, and inspection that make it continuous. (1.1)
NOTE A vapor retarder limits the diffusion of water vapor through a material and is rated by its water vapor permeance in perms. The trade term "vapor barrier" describes the least permeable retarders, those at or below 0.1 perm, but every product in this standard is a vapor retarder of a defined class. (1.2)
NOTE Diffusion through an intact material moves far less water than air leakage through gaps, laps, and unsealed penetrations does under the same conditions. A vapor retarder therefore protects an assembly only where the air barrier is continuous, and the air barrier is specified in Air BarriersAir BarriersResolves to the current adopted revision.sync/air-barriers. (1.3)
NOTE The side of the insulation on which the retarder is placed decides whether it protects the assembly or damages it. A retarder on the warm side slows wetting; the same retarder on the cold side holds a condensing surface against the moisture that reaches it and blocks the drying path, converting a seasonal wetting event into accumulated water. (1.4)
NOTE The following products and applications perform a vapor retarder function and are specified elsewhere: (1.5)
  • The sheet installed under a slab-on-grade in contact with soil or granular fill, including its ASTM E1745 class, placement relative to the slab, laps, and penetrations, is specified in Vapor Barriers Under SlabUnder-Slab Vapor BarriersResolves to the current adopted revision.sync/vapor-barriers-under-slab; a standard that refers here for that material is served by that standard
  • Kraft and foil facings on cavity insulation, closed-cell spray polyurethane foam, and low-permeance foam board that serve as the assembly's vapor retarder are specified in Building Thermal InsulationBuilding Thermal InsulationResolves to the current adopted revision.sync/building-thermal-insulation, which also records the assembly thermal values this standard's continuous insulation ratio depends on
  • The vapor retarder on the roof deck below the insulation of a membrane roof is specified in Membrane RoofingMembrane RoofingResolves to the current adopted revision.sync/membrane-roofing
  • The exterior air barrier membrane and its vapor permeance class are specified in Air BarriersAir BarriersResolves to the current adopted revision.sync/air-barriers; an interior sheet vapor retarder that is also sealed as the building's air barrier is specified here, and its air leakage performance and verification are governed by Air BarriersAir BarriersResolves to the current adopted revision.sync/air-barriers
  • Dampproofing and waterproofing of below-grade foundation walls are specified in DampproofingDampproofingResolves to the current adopted revision.sync/dampproofing and Below Grade WaterproofingBelow-Grade WaterproofingResolves to the current adopted revision.sync/below-grade-waterproofing
1.6 The vapor retarder shall comply with the vapor retarder provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code and with the manufacturer's published installation instructions.

2 Referenced Standards

2.1 Materials and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 Where the contract documents, the adopted code, the manufacturer's instructions, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
Standard Title
IBC International Building Code (Chapter 14 vapor retarder provisions)
IRC International Residential Code (Section R702.7 vapor retarders; Section R806 roof ventilation and unvented assemblies)
ASTM E96/E96M Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
ASTM D4397 Standard Specification for Polyethylene Sheeting for Construction, Industrial, and Agricultural Applications
ASTM D882 Standard Test Method for Tensile Properties of Thin Plastic Sheeting
ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials
ASTM E2178 Standard Test Method for Determining Air Leakage Rate and Calculation of Air Permeance of Building Materials
ASHRAE 160 Criteria for Moisture-Control Design Analysis in Buildings

3 Submittals

3.1 Action Submittals

NOTE A permeance value without the test procedure beside it cannot be classified: the desiccant and water procedures of ASTM E96 hold the specimen at different mean relative humidities and return different values for the same material, and a variable-permeance membrane is defined by the gap between the two. (3.1.1)
3.1.2 The Contractor shall submit the following for the Engineer of Record's review and return before procurement and installation:
  • Product data for each vapor retarder, reporting the water vapor permeance per ASTM E96 with the procedure used, the resulting vapor retarder class, the nominal thickness of sheet products, and the surface burning characteristics per ASTM E84 where the retarder will remain exposed
  • For a variable-permeance membrane, the permeance by the desiccant procedure and by the water procedure of ASTM E96, and the permeance across the relative humidity range the manufacturer publishes
  • For a vapor retarder coating, the dry film thickness or spreading rate at which the reported permeance was tested
  • Product data for seam tape, sealant, box enclosures, and penetration accessories, with the manufacturer's written confirmation that each is compatible with the vapor retarder
  • Where the vapor retarder is sealed as the interior air barrier, the material air permeance per ASTM E2178
  • Where the design basis is a hygrothermal analysis, the analysis report prepared by the Engineer of Record, included for the Contractor's information
  • The manufacturer's installation instructions for each product
Action Submittals Requiredcheckbox
☑ Vapor retarder product data with permeance, ASTM E96 procedure, and class
☐ Variable-permeance membrane desiccant and water procedure permeance data
☐ Vapor retarder coating tested film thickness or spreading rate
☑ Seam tape, sealant, and accessory data with compatibility confirmation
☐ Material air permeance per ASTM E2178 where sealed as the air barrier
☐ Hygrothermal analysis report where that is the design basis
☑ Manufacturer installation instructions

3.2 Closeout Submittals

NOTE The inspection record is the only durable evidence of the class installed and the side it was installed on, because neither can be verified once the gypsum board is up without opening the wall. (3.2.1)
3.2.2 At Substantial Completion the Contractor shall submit the following before the vapor retarder work is accepted:
  • The inspection record for each area concealed, identifying the product installed, the side of the insulation it occupies, and the acceptance of seams, penetrations, and terminations before concealment
  • A record of each repair made before concealment, with its location and method
  • For a vapor retarder coating, the wet film thickness readings taken during application
  • Executed installer and manufacturer warranties
Closeout Submittals Requiredcheckbox
☑ Inspection records before concealment
☑ Repair records with location and method
☐ Vapor retarder coating wet film thickness readings
☑ Executed installer and manufacturer warranties

4 Quality Assurance

4.1 The vapor retarder installer shall have installed the type of vapor retarder specified on completed projects of comparable assembly type, and shall submit a record of those projects on request.
4.2 Where the vapor retarder is sealed as the interior air barrier, the installer shall meet the installer qualification specified in Air BarriersAir BarriersResolves to the current adopted revision.sync/air-barriers.
4.3 Before the first vapor retarder is installed, the Contractor shall confirm in writing with the insulation, gypsum board, electrical, plumbing, and mechanical trades which trade seals each penetration and box through the retarder and in what sequence.
NOTE Penetrations of an interior vapor retarder are made by trades that arrive after the installer has left, and a box or pipe that no trade was told to seal stays open. (4.4)

5 Vapor Control Design Basis

NOTE The adopted code tabulates the vapor retarder class an assembly needs by climate zone, on the assumption of an ordinary interior humidity. Where the interior will be humidified, or will run at an elevated relative humidity through the heating season, the vapor drive outward is larger than that table assumes, and the class and position are established by analysis instead. (5.1)
5.2 The vapor retarder class and position shall be established on the basis indicated in the datasheet.
Vapor Retarder Design Basisradio
● Prescriptive class and position from the vapor retarder provisions of the adopted building code for the climate zone
○ Hygrothermal analysis per ASHRAE 160
5.3 Where the building is mechanically humidified during the heating season, or where the mechanical design documents state a heating-season interior relative humidity above the interior conditions the code's prescriptive vapor retarder provisions assume, the design basis shall be a hygrothermal analysis per ASHRAE 160.
5.4 Where the design basis is a hygrothermal analysis, the Engineer of Record shall prepare the analysis and shall state in it the class and the position of the vapor retarder for each assembly.
5.5 The cross-cutting declaration of when a moisture-control analysis is required for the envelope is made in Thermal And Moisture Protection Common ResultsCommon Work Results for Thermal and Moisture ProtectionResolves to the current adopted revision.sync/thermal-and-moisture-protection-common-results; this standard applies that analysis to the vapor retarder it governs.

6 Wall Vapor Retarder Class

NOTE Vapor retarders are classified by water vapor permeance determined by the desiccant procedure of ASTM E96: Class I is 0.1 perm or less, Class II is greater than 0.1 perm through 1.0 perm, and Class III is greater than 1.0 perm through 10 perm. Polyethylene sheet and foil laminates fall in Class I, asphalt-coated kraft and most vapor retarder coatings in Class II, and latex paint on gypsum board in Class III. (6.1)
NOTE In the cold and very cold zones and the marine zone the code requires a Class I or Class II retarder on the interior side of a frame wall, because the heating-season drive carries interior moisture outward to the cold sheathing. In the mixed zone it permits any class. In the hot and warm zones it requires none, and the dominant drive is inward, so a low-permeance interior layer there holds inward-driven moisture against the back of the interior finish. (6.2)
NOTE The code permits a Class III retarder in place of the Class I or Class II it would otherwise require where the exterior continuous insulation reaches the ratio it tabulates for the climate zone, because continuous insulation outboard of the sheathing holds the sheathing above the dew point of the interior air. The code also accepts a variable-permeance membrane in place of a Class I or Class II retarder where the membrane meets the code's criteria for a responsive vapor retarder. (6.3)
6.4 The vapor retarder class for above-grade walls shall be as indicated in the datasheet.
Wall Vapor Retarder Classradio
○ Class I — 0.1 perm or less
○ Class II — greater than 0.1 perm through 1.0 perm
○ Class III — greater than 1.0 perm through 10 perm
○ No dedicated vapor retarder
Derived — the vapor retarder provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code for Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone, the wall assembly's exterior continuous insulation ratio, and the hygrothermal analysis where that is the design basis (by default)
6.5 Where the project relies on the continuous insulation ratio to permit a Class III vapor retarder, the ratio shall be calculated by the Engineer of Record from the assembly thermal values recorded in Building Thermal InsulationBuilding Thermal InsulationResolves to the current adopted revision.sync/building-thermal-insulation and shall be stated in the contract documents.
6.6 A Class I vapor retarder shall not be installed on the interior side of a frame wall where the vapor retarder provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code prohibit it for Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone, unless a hygrothermal analysis per ASHRAE 160 demonstrates that the assembly dries under the project design conditions.
6.7 An assembly shall not contain a Class I or Class II vapor retarder on both the interior and exterior sides of the cavity insulation, unless a hygrothermal analysis per ASHRAE 160 demonstrates that the assembly dries under the project design conditions.
NOTE Two low-permeance layers on opposite sides of the insulation leave the moisture between them no path to dry in either direction. The exterior layer is often not a vapor retarder by name: foil-faced sheathing, a low-permeance exterior air barrier, and closed-cell foam in the cavity each place a Class I or Class II layer outboard of the cavity, and an interior sheet added by habit over any of them creates the condition. (6.8)
6.9 The Contractor shall not substitute a vapor retarder of a different class, or a material whose permeance by the same ASTM E96 procedure differs from the reviewed product, without a revised assembly evaluation by the Engineer of Record.

7 Wall Vapor Retarder Position

NOTE A dedicated vapor retarder occupies one of three positions in a framed wall. On the interior face of the framing, directly behind the interior finish, it is on the warm side of all the insulation and is the position the code's climate zone table assumes. Inboard of a service cavity, with up to one-third of the cavity's thermal resistance on its interior side, it stays warm enough to avoid condensation while wiring and boxes run inside it without penetrating it. On the exterior side of the cavity insulation, inboard of the continuous insulation, it is a position only the continuous insulation ratio makes safe, and it is used where the retarder is also the air barrier plane at the sheathing. (7.1)
7.2 The vapor retarder shall be installed at the position in the wall assembly indicated in the datasheet.
Wall Vapor Retarder Positionradio
● Interior face of the framing, directly behind the interior finish
○ Inboard face of a service cavity, with the cavity insulation outboard of it
○ Exterior side of the cavity insulation, inboard of the continuous insulation
7.3 Where the vapor retarder is placed inboard of a service cavity, the thermal resistance of the insulation on its interior side shall not exceed one-third of the total thermal resistance of the assembly's insulation, unless a hygrothermal analysis per ASHRAE 160 permits a greater share.
7.4 Where the vapor retarder is placed on the exterior side of the cavity insulation, the exterior continuous insulation shall meet the ratio the vapor retarder provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code tabulate for Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone, or the position shall be supported by a hygrothermal analysis per ASHRAE 160.

8 Ceiling and Framed Roof Assembly Vapor Retarder

NOTE A ceiling below a vented attic dries into the attic air, so the code requires no vapor retarder there in most zones and the attic ventilation carries the moisture away. An unvented roof assembly has no such path: the code regulates it by the kind of insulation in contact with the roof deck, and in the colder zones it requires a Class II retarder on the interior side of air-permeable cavity insulation under air-impermeable insulation. The ceiling retarder is a separate decision from the wall retarder because the same building can need one at the walls and none at the ceiling. (8.1)
8.2 The vapor retarder class for the ceiling plane and for framed roof assemblies with cavity insulation shall be as indicated in the datasheet.
Ceiling and Framed Roof Vapor Retarder Classradio
○ Class I — 0.1 perm or less
○ Class II — greater than 0.1 perm through 1.0 perm
○ Class III — greater than 1.0 perm through 10 perm
○ No dedicated vapor retarder
Derived — the attic ventilation and unvented roof assembly provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code for Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone, whether the attic or roof assembly is vented, and the hygrothermal analysis where that is the design basis (by default)
8.3 Where a vapor retarder is installed at the ceiling plane, it shall be on the interior side of the ceiling insulation, directly behind the ceiling finish.
8.4 A ceiling vapor retarder shall not be installed below a vented attic where the attic ventilation provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code rely on the absence of one for Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone.
8.5 Where the roof is a membrane roof, the vapor retarder on the roof deck is specified in Membrane RoofingMembrane RoofingResolves to the current adopted revision.sync/membrane-roofing, and the retarder in this article shall not be installed in addition to it without a hygrothermal analysis per ASHRAE 160.

9 Vapor Retarder Materials

9.1 Material Selection

NOTE Each product reaches a different class by a different mechanism, and the one that fits depends on the class the assembly needs, whether the assembly must dry inward in summer, whether the retarder also serves as the air barrier, and whether it goes in before or after the interior finish. (9.1.1)
  • Polyethylene sheet is the lowest-cost Class I retarder and the easiest to seal as an air barrier, and it blocks inward drying entirely, so it suits assemblies with a dry exterior side in a heating-dominated climate and nothing else
  • Reinforced polyethylene sheet adds a scrim that resists tearing at staples and at traffic before the finish goes on, and is the product used where the retarder stays exposed, as in unfinished storage, agricultural, and industrial interiors
  • Foil-laminate sheet is the lowest-permeance product available and adds a low-emissivity surface facing an air space, which fits the humidified occupancies that need a true barrier, and its combustible facing limits where it can be left exposed
  • A variable-permeance membrane is Class I or Class II when the surrounding air is dry and opens to several perms when it is humid, so it resists the heating-season drive outward and still lets the assembly dry inward in summer, at a cost several times that of polyethylene
  • A vapor retarder coating on gypsum board reaches Class II or Class III at its tested film build, has no seams, and is the only option that can be added after the wall is closed, and it provides no air barrier at the board joints and depends on the film build being reached everywhere
9.1.2 The vapor retarder material shall be as indicated in the datasheet.
Vapor Retarder Materialradio
○ Polyethylene sheet
○ Reinforced polyethylene sheet
○ Foil-laminate sheet
○ Variable-permeance membrane
○ Vapor retarder coating on gypsum board
9.1.3 The material indicated in the datasheet shall have a permeance, by the ASTM E96 procedure the adopted code names for classification, within the vapor retarder class indicated for the assembly it serves.
9.1.4 A vapor retarder that remains exposed in an occupied space, an attic, or a plenum shall have a flame spread index not greater than 25 and a smoke-developed index not greater than 450 per ASTM E84, unless Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code permits a higher index for that location.

9.2 Polyethylene Sheet

9.2.1 Polyethylene sheet shall conform to ASTM D4397 and shall have a nominal thickness not less than that indicated in the datasheet.
Polyethylene Sheet Nominal Thicknessrange
Not less than
mil
46810
NOTE Four mil is the thinnest sheet the code accepts as a Class I retarder and tears readily at staples; six mil is the thickness the code and most installation instructions name; eight and ten mil are used where the sheet is walked on, stays exposed, or is also the air barrier and must survive the sealing work at every lap. (9.2.2)
9.2.3 Reinforced polyethylene sheet shall be a scrim-reinforced polyethylene laminate with the tensile strength per ASTM D882 and the permeance per ASTM E96 reported in the product data.

9.3 Foil-Laminate Sheet

9.3.1 Foil-laminate sheet shall be an aluminum foil laminated to a reinforcing scrim and a kraft or polymer backing, with a permeance by the desiccant procedure of ASTM E96 not greater than 0.1 perm.
9.3.2 Foil-laminate sheet shall be installed with its foil face toward the air space where the assembly includes an air space on the warm side of the retarder.

9.4 Variable-Permeance Membrane

9.4.1 A variable-permeance membrane shall be Class I or Class II by the desiccant procedure of ASTM E96 and shall have a permeance greater than 1 perm by the water procedure of ASTM E96, and shall meet the criteria the vapor retarder provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code set for a responsive vapor retarder.
9.4.2 A variable-permeance membrane shall be installed with the face the manufacturer designates toward the interior, where the manufacturer designates one.

9.5 Vapor Retarder Coating

9.5.1 A vapor retarder coating shall be applied to the gypsum board at not less than the spreading rate, and in not fewer than the coats, at which the manufacturer tested the reported permeance.
9.5.2 The Contractor shall measure wet film thickness with a gauge at not less than one location per 500 square feet of coated surface and shall record the readings.
9.5.3 The coating shall be applied after the gypsum board joints are finished and before any finish paint, and its application shall be coordinated with Gypsum Board AssembliesGypsum Board AssembliesResolves to the current adopted revision.sync/gypsum-board-assemblies and Interior PaintingInterior PaintingResolves to the current adopted revision.sync/interior-painting.
9.5.4 A finish paint applied over a vapor retarder coating shall be one the coating manufacturer identifies as compatible.

10 Air Barrier Function of the Vapor Retarder

NOTE Whether the interior vapor retarder is also the building's air barrier is a separate decision from its class. A sheet retarder sealed at every lap, edge, box, and penetration can serve as the air barrier; the same sheet stapled up and cut around boxes controls diffusion only. The sealed sheet doubles the labor at every penetration and ties the installer to the air barrier verification, and where the building has an exterior air barrier it adds a second plane whose continuity must also be proven. (10.1)
10.2 The air barrier function of the vapor retarder shall be as indicated in the datasheet.
Air Barrier Function of the Vapor Retarderradio
○ The vapor retarder serves no air barrier function
○ The vapor retarder is sealed as the interior air barrier
10.3 Where the vapor retarder is sealed as the interior air barrier, it shall meet the material air permeance limit, the continuity requirements, and the field verification specified in Air BarriersAir BarriersResolves to the current adopted revision.sync/air-barriers, and shall be made continuous with the air barrier of every adjoining assembly.
10.4 Where the vapor retarder is sealed as the interior air barrier, every lap, edge, box, and penetration shall be sealed, and the box treatment indicated in the datasheet shall be one that seals the box to the sheet.

11 Installation

11.1 Substrate and Sequence

11.1.1 The vapor retarder shall be installed only after the cavity insulation is in place and inspected, and after the framing and sheathing have dried to a moisture content the interior finish standard accepts.
NOTE A sheet retarder installed over wet framing seals the water in with the assembly, and the first heating season moves it to the sheathing. (11.1.2)
11.1.3 The vapor retarder shall be installed over a surface free of fasteners, splinters, and projections that would puncture it, and shall not be stretched tight across framing.

11.2 Sheet Laps and Seams

11.2.1 Sheet vapor retarder laps shall occur over a framing member or a solid backing and shall be not less than the width indicated in the datasheet.
Sheet Lap Widthrange
Not less than
in.
24612
NOTE A lap of 2 inches holds only where a tape or an adhesive strip carries the seal; a lap over a framing member of 6 inches lets the lap be clamped by the finish and sealed with either tape or sealant; a 12 inch lap is used where the sheet is also the air barrier and the lap cannot be backed by framing. (11.2.2)
11.2.3 Laps and seams shall be sealed by the method indicated in the datasheet.
Seam Sealing Methodradio
○ Manufacturer's seam tape over the lap
○ Continuous bead of compatible sealant within the lap, clamped at the framing
○ Seam tape over the lap and sealant bead within the lap
○ Not applicable — vapor retarder coating with no seams
Manufacturer's standard (by default)
NOTE Tape seals on the face of the sheet, is checked by eye, and depends on a clean, dry sheet and on the tape's adhesion to that polymer; a sealant bead within the lap is clamped by the framing and stays sealed through movement, and is invisible once the lap is closed. The two together are used where the sheet is the air barrier and the lap will be tested. (11.2.4)
11.2.5 Seam tape and sealant shall be products the vapor retarder manufacturer identifies as compatible with the sheet, applied to a clean and dry surface within the temperature range the tape or sealant manufacturer publishes.

11.3 Penetrations and Electrical Boxes

11.3.1 Each penetration of the vapor retarder by piping, ducts, conduit, and structural members shall be sealed to the penetrating element with tape, sealant, or a preformed collar the vapor retarder manufacturer identifies as compatible.
11.3.2 Electrical boxes in the vapor retarder plane shall be treated by the method indicated in the datasheet.
Electrical Box Treatmentradio
○ Airtight electrical box with integral flange sealed to the sheet
○ Preformed box enclosure sealed to the sheet and to the cable entries
○ Sheet cut to the box and sealed to its perimeter with tape or sealant
○ Box cut-outs left unsealed
○ Not applicable — vapor retarder coating on the gypsum board
NOTE An airtight box carries its own flange and is sealed once, by the electrician setting it; a preformed enclosure goes over an ordinary box and is sealed to the sheet and at each cable; a sheet cut to the box and taped is the cheapest and the first to open when the box is worked. Cut-outs left unsealed are a diffusion path small enough to ignore and an air leak large enough not to, so they are an option only where the sheet serves no air barrier function. (11.3.3)
11.3.4 Each penetration and box shall be sealed by the trade identified for it in the written trade confirmation required under Quality Assurance, and a penetration made after the retarder is installed shall be sealed by the trade that made it using the materials specified here.

11.4 Terminations and Transitions

11.4.1 The vapor retarder shall be continuous across the face of the assembly it serves and shall be sealed to the framing at the top plate, the bottom plate, and each side of every opening, and at its termination to the adjoining floor, ceiling, and wall assemblies.
11.4.2 Where the wall vapor retarder meets a ceiling vapor retarder, the two shall be lapped and sealed to each other.
11.4.3 At an intersecting interior partition, the vapor retarder shall be carried continuously across the end of the partition before the partition is framed, or shall be sealed to a strip of the same material installed across the end of the partition.
11.4.4 Where the vapor retarder meets a window or door frame, it shall be sealed to the frame or to the air barrier flashing at the opening, using materials each manufacturer confirms as compatible.

11.5 Repairs

11.5.1 Vapor retarder material that is cut, torn, or punctured shall be repaired before the assembly is concealed with a patch of the same material lapped not less than 6 inches onto sound material on every side and sealed with the seam sealing method indicated in the datasheet.
11.5.2 Where the parties disagree whether a repair is adequate, the Engineer of Record shall make the initial determination.

12 Field Quality Control

12.1 Inspection Before Concealment

NOTE A vapor retarder of the wrong class or on the wrong side looks identical to the right one through a finished wall. The inspection before the gypsum board goes on is the only point at which either can be confirmed, so it is a hold point rather than a punch-list item. (12.1.1)
12.1.2 The Contractor shall give the Engineer of Record notice before concealing any portion of the vapor retarder, at the notice interval the Contract Documents establish.
12.1.3 Each area of vapor retarder shall be inspected for the product installed, the side of the insulation it occupies, continuous laps, sealed penetrations and boxes, and sealed terminations, and shall be accepted before it is concealed by gypsum board, furring, or finishes.
12.1.4 For a vapor retarder coating, the inspection shall confirm the recorded wet film thickness readings against the tested spreading rate before any finish paint is applied.
12.1.5 Work concealed without the required inspection shall be uncovered for inspection at the Contractor's expense where the Engineer of Record directs.

13 Delivery, Storage, and Handling

13.1 Vapor retarder materials shall be delivered in the manufacturer's original labeled packaging with the product designation and class legible.
13.2 Sheet materials shall be stored off the ground, under cover, and protected from sunlight, crushing, and puncture until installed.
NOTE Polyethylene embrittles under ultraviolet exposure, and a roll that has sat in the sun on site carries that damage into the wall where it cannot be seen. (13.3)
13.4 Seam tape, sealant, and coating shall be stored within the temperature range the manufacturer publishes, and material past its shelf-life expiration date shall be removed from the site.

14 Warranty

14.1 Installer Warranty

14.1.1 The Contractor shall warrant the vapor retarder installation against defective laps, seams, penetration seals, and terminations, and against installation of a class or at a position other than the one indicated, for the period indicated in the datasheet from the date of Substantial Completion.
Installer Warranty Periodrange
Not less than
years
125
14.1.2 The Contractor shall bear the cost of correcting moisture damage to the assembly attributable to a defect covered by the installer warranty, including the cost of removing and reinstalling finishes and insulation required to reach the defect.
14.1.3 Work repaired under warranty shall be warranted for a full warranty term running from the date of the repair, or for the unexpired remainder of the original term, whichever ends later.

14.2 Manufacturer Material Warranty

14.2.1 The Contractor shall provide the vapor retarder manufacturer's material warranty for the period indicated in the datasheet.
Manufacturer Material Warranty Periodrange
Not less than
years
15101520
14.2.2 Where no manufacturer material warranty period is indicated in the datasheet, the period the manufacturer publishes for the specified product shall govern, and that period shall be stated in the product data submittal.

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