Vapor Retarders
Remade for neutrality: every choice explained, project facts as parameters, scope boundaries linked both ways
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to Rev 4
in Vapor Retarders.
---
title: Vapor Retarders
category: Building Envelope
−toc_depth: 3
description: >
− When to use: Below-slab vapor barriers under concrete slabs-on-grade and above-grade wall and ceiling vapor retarders for moisture and water-vapor control in commercial, institutional, and residential buildings. Covers the two distinct applications addressed by this standard: (1) the plastic sheet water-vapor retarder installed in contact with soil or granular fill beneath a concrete slab-on-grade, classified to ASTM E1745 (Class A, B, or C) and installed to ASTM E1643, with its thickness, permeance, lapped and taped seams, sealed penetrations and pipe boots, and the placement debate of ACI 302.1R / 302.2R over whether the retarder sits directly under the slab or below a granular cushion; and (2) the above-grade vapor retarder in framed wall and ceiling assemblies, classified by permeance as IBC/IRC Class I, II, or III, placed on the correct (warm-in-winter) side of the assembly governed by climate zone, including kraft-faced batt facings, polyethylene sheet, and variable-permeance (smart) membranes. Addresses class selection, permeance verification per ASTM E96, climate-zone placement logic, seam and penetration sealing, and field inspection before concealment.
− Not intended for: Air barriers, whose function is to stop bulk air movement rather than vapor diffusion (see [[sync/air-barriers]]); below-grade dampproofing and waterproofing of foundation walls and slabs that retain earth and resist liquid water and hydrostatic pressure (see [[sync/below-grade-waterproofing]]); roofing vapor control layers furnished as part of a low-slope or steep-slope roof assembly (see [[sync/membrane-roofing]]); the thermal insulation itself, even where its facing also serves as a vapor retarder (see [[sync/building-thermal-insulation]]); and the concrete slab mix, finishing, and curing (see [[sync/cast-in-place-concrete]]).
+ When to use: Dedicated vapor retarder products installed in above-grade framed and furred wall assemblies, in the ceiling plane below a vented attic, and in framed roof assemblies with cavity insulation, in commercial, institutional, multifamily, and residential buildings. Covers the vapor retarder class the adopted code requires for the climate zone and assembly, the position of the retarder within the assembly, the products that provide it (polyethylene sheet, reinforced polyethylene sheet, foil-laminate sheet, variable-permeance membranes, and vapor retarder coatings on gypsum board), seams, penetrations and electrical boxes, perimeter terminations, the retarder's optional role as the interior air barrier, inspection before concealment, and warranty.
+ Not intended for: The sheet installed in contact with soil or granular fill beneath a slab-on-grade, including its ASTM E1745 class, placement, seams, and penetrations (see [[sync/vapor-barriers-under-slab]]); insulation facings, closed-cell spray polyurethane foam, and low-permeance foam board that serve as the assembly's vapor retarder (see [[sync/building-thermal-insulation]]); the vapor retarder installed on the roof deck below the insulation of a membrane roof (see [[sync/membrane-roofing]]); the exterior air barrier membrane and its vapor permeance class (see [[sync/air-barriers]]); and dampproofing and waterproofing of below-grade foundation walls (see [[sync/dampproofing]] and [[sync/below-grade-waterproofing]]).
---
# Scope {toc}
−## This standard covers the materials, classification, placement, and installation of vapor retarders in two distinct applications: the below-slab vapor barrier installed in contact with soil or granular fill under a concrete slab-on-grade, and the above-grade vapor retarder installed within framed wall and ceiling assemblies. {note}
−## Although both applications control the diffusion of water vapor, they are governed by different standards, classified on different scales, and placed by different logic, so the two are specified separately within this standard and shall not be confused with one another. {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. {note}
−## A vapor retarder is a material that limits the rate at which water vapor diffuses through a building assembly, rated by its water-vapor permeance in perms. {note}
−## The term "vapor barrier" is used loosely in the field for the most impermeable retarders (Class I, at or below 0.1 perm), but every product in this standard is more precisely a vapor retarder of a defined class; this standard uses "below-slab vapor barrier" for the under-slab sheet by industry convention and "vapor retarder" for the above-grade material. {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. {note}
−## The single most consequential decision in this standard is which side of the assembly the vapor retarder is placed on, because a retarder placed on the wrong side traps moisture against a cold surface and condenses it inside the assembly, causing exactly the damage the retarder was meant to prevent. {note}
−## For below-slab work, the governing question is instead whether the retarder is placed directly beneath the slab or below a granular cushion, a placement choice with real consequences for slab curling, bleed water, and floor-covering moisture that this standard addresses explicitly. {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 [[sync/air-barriers]]. {note}
−## A vapor retarder is not an air barrier, and the two shall not be substituted for one another: the vapor retarder controls diffusion of vapor through a material, while the air barrier controls bulk air leakage through gaps and laps, which carries far more moisture than diffusion ever does. {note}
−## The air barrier scope is covered by [[sync/air-barriers]] and is referenced, not duplicated, here. {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. {note}
−## The below-slab vapor barrier shall not be confused with below-grade waterproofing: the under-slab sheet resists upward water-vapor diffusion from the ground, not liquid water under hydrostatic pressure, which is the scope of [[sync/below-grade-waterproofing]].
+## The following products and applications perform a vapor retarder function and are specified elsewhere: {note}
−## All work shall comply with the adopted edition of the International Building Code (IBC) and International Residential Code (IRC), the referenced ASTM standards and ACI guides, and the vapor retarder manufacturer's published installation instructions.
+- 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 [[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 [[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 [[sync/membrane-roofing]]
+- The exterior air barrier membrane and its vapor permeance class are specified in [[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 [[sync/air-barriers]]
+- Dampproofing and waterproofing of below-grade foundation walls are specified in [[sync/dampproofing]] and [[sync/below-grade-waterproofing]]
+## The vapor retarder shall comply with the vapor retarder provisions of [[parameter: adopted-building-code]] and with the manufacturer's published installation instructions.
+
# Referenced Standards {toc}
−## Materials, classification, testing, and installation shall comply with the latest adopted editions of the standards and codes listed below.
−## Where the contract documents, the adopted building 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.
+## Materials and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+## 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 (Exterior Walls), vapor retarder provisions |
−| IRC Section R702.7 | International Residential Code — Vapor Retarders (Class I/II/III by climate zone) |
−| ASTM E1745 | Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs (Class A, B, C) |
−| ASTM E1643 | Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill under Concrete Slabs |
−| ASTM E1993 | Standard Specification for Bituminous Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs |
−| ASTM E96 / E96M | Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials (perm rating; wet-cup and dry-cup) |
−| ASTM E154 / E154M | Standard Test Methods for Water Vapor Retarders Used in Contact with Earth under Concrete Slabs, on Walls, or as Ground Cover (conditioning) |
+| 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 D1709 | Standard Test Methods for Impact Resistance of Plastic Film by the Free-Falling Dart Method (puncture resistance) |
−| ASTM F1249 | Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor |
−| ACI 302.1R | Guide to Concrete Floor and Slab Construction (vapor retarder placement) |
−| ACI 302.2R | Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials |
+| 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 |
−## Materials, classification, testing, and installation shall comply with the latest adopted editions of the referenced standards and codes.
−## Where the contract documents, the 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.
−
# Submittals {toc}
## Action Submittals {toc}
−### The vapor retarder, its seam tape, and its penetration accessories must be submitted together as a coordinated set, because the seam and penetration seals are where below-slab and above-grade retarders most often fail. {note}
−### The Contractor shall submit the items listed below for the Engineer's review and return before procurement and installation.
+### 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. {note}
−- Product data for each vapor retarder, stating the water-vapor permeance per ASTM E96 (and the resulting IBC/IRC vapor retarder class for above-grade materials, or the ASTM E1745 / E1993 class for below-slab materials), the nominal thickness in mils, and the tensile strength and puncture resistance for below-slab sheet
−- For below-slab vapor barriers: certification of the ASTM E1745 class (A, B, or C), including the permeance measured both before and after the ASTM E154 conditioning regimen
−- Product data for the matched seam tape, pipe boots, and pre-formed accessories supplied or approved by the vapor retarder manufacturer
−- For above-grade variable-permeance (smart) membranes: the dry-cup and wet-cup permeance values demonstrating the responsive permeance range
−- A sample of each vapor retarder and of the seam tape
−- A placement plan for below-slab work identifying whether the vapor barrier is placed directly beneath the slab or below a granular cushion, with the basis for that decision coordinated with the structural engineer and ACI 302.1R / 302.2R
+### 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
…2 unchanged lines
type: checkbox
options:
− - "Vapor retarder product data (permeance per E96, class, thickness)"
− - "Below-slab ASTM E1745 class certification (permeance before and after E154 conditioning)"
− - "Matched seam tape, pipe boots, and accessory product data"
− - "Variable-permeance (smart) membrane dry-cup and wet-cup permeance data"
− - "Samples of each vapor retarder and seam tape"
− - "Below-slab placement plan (direct under slab vs over granular cushion)"
− - "Manufacturer installation instructions for each product"
+ - "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"
default:
− - "Vapor retarder product data (permeance per E96, class, thickness)"
+ - "Vapor retarder product data with permeance, ASTM E96 procedure, and class"
+ - "Seam tape, sealant, and accessory data with compatibility confirmation"
+ - "Manufacturer installation instructions"
```
−### The Contractor shall submit the action submittal items listed above for the Engineer's review and return before procurement and installation.
−### Installation shall not proceed until the corresponding submittals have been reviewed and returned without rejection.
−
## Closeout Submittals {toc}
−### At substantial completion, the Contractor must provide the closeout records listed below before the vapor retarder work is accepted.
+### 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. {note}
−- Daily installation and inspection records, including the ambient and substrate conditions at the time of installation
−- The pre-placement inspection record for the below-slab vapor barrier, documenting that laps, seams, penetrations, and any repairs were inspected and accepted before concrete placement
−- A record of any damage found and repaired, identifying the location and repair method
−- Manufacturer's warranty documentation for products carrying a manufacturer warranty
+### 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
+
```datasheet
label: Closeout Submittals Required
type: checkbox
options:
− - "Daily installation and inspection records (ambient and substrate conditions)"
− - "Pre-placement inspection record for below-slab vapor barrier (before concrete)"
− - "Record of damage found and repaired (location and method)"
− - "Manufacturer warranty documentation where applicable"
−default: "Pre-placement inspection record for below-slab vapor barrier (before concrete)"
+ - "Inspection records before concealment"
+ - "Repair records with location and method"
+ - "Vapor retarder coating wet film thickness readings"
+ - "Executed installer and manufacturer warranties"
+default:
+ - "Inspection records before concealment"
+ - "Repair records with location and method"
+ - "Executed installer and manufacturer warranties"
```
−### The Contractor shall provide the closeout submittals listed above at substantial completion before the vapor retarder work is accepted.
−
# Quality Assurance {toc}
−## Installer Qualifications {toc}
+## 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.
−### Vapor retarder work is simple to install but unforgiving of inattention, because a single unsealed lap or an unsealed pipe penetration in a below-slab barrier is permanently concealed once the slab is poured and cannot be reached for repair. {note}
+## Where the vapor retarder is sealed as the interior air barrier, the installer shall meet the installer qualification specified in [[sync/air-barriers]].
−### The vapor retarder installer shall be experienced in the installation of the type of vapor retarder being installed and shall install it in accordance with ASTM E1643 (below-slab) or the manufacturer's instructions (above-grade).
+## 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.
−```datasheet
−label: Installer Qualification Basis
−type: radio
−options:
− - "Experienced installer following ASTM E1643 and manufacturer instructions (standard)"
− - "Manufacturer-trained installer for the specific below-slab system"
−default: "Experienced installer following ASTM E1643 and manufacturer instructions (standard)"
−```
+## 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. {note}
−## Pre-Placement Inspection {toc}
+# Vapor Control Design Basis {toc}
−### The below-slab vapor barrier shall be inspected and accepted before any concrete is placed, because once the slab is poured no defect in the barrier can be located or corrected without demolition.
+## 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. {note}
+## The vapor retarder class and position shall be established on the basis indicated in the datasheet.
+
```datasheet
−label: Below-Slab Pre-Placement Inspection
+label: Vapor Retarder Design Basis
type: radio
options:
− - "Required; laps, seams, and penetrations inspected and accepted before concrete placement (standard)"
− - "Not required (vapor barrier not specified for this slab)"
−default: "Required; laps, seams, and penetrations inspected and accepted before concrete placement (standard)"
+ - "Prescriptive class and position from the vapor retarder provisions of the adopted building code for the climate zone"
+ - "Hygrothermal analysis per ASHRAE 160"
+default: "Prescriptive class and position from the vapor retarder provisions of the adopted building code for the climate zone"
```
−### The Contractor shall not place concrete over the below-slab vapor barrier until the installed barrier, its laps and seams, and all penetration seals have been inspected and accepted.
−### Any damage to the below-slab vapor barrier discovered before concrete placement shall be repaired and re-inspected.
+## 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.
−## Moisture-Sensitive Flooring Coordination {toc}
+## 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.
−### Where the slab will receive a moisture-sensitive floor covering or coating, the vapor barrier is not optional, and its placement directly beneath the slab is the current recommendation of ACI Committee 302 precisely to protect that flooring from slab moisture. {note}
+## The cross-cutting declaration of when a moisture-control analysis is required for the envelope is made in [[sync/thermal-and-moisture-protection-common-results]]; this standard applies that analysis to the vapor retarder it governs.
−### Where the slab-on-grade will receive a moisture-sensitive floor covering, adhesive, or coating, a below-slab vapor barrier conforming to ASTM E1745 shall be provided.
−### The vapor barrier placement and the slab moisture acceptance criteria shall be coordinated with [[sync/cast-in-place-concrete]] and with the flooring manufacturer's maximum allowable moisture-vapor emission rate and internal relative humidity.
+# Wall Vapor Retarder Class {toc}
−# Environmental and Service Conditions {toc}
+## 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. {note}
−## The correct vapor retarder strategy depends entirely on climate, because the direction of the dominant vapor drive — and therefore the side of the assembly that must be protected — reverses between cold heating-dominated climates and hot-humid cooling-dominated climates. {note}
−## In a cold climate the vapor drive in winter is from the warm, humid interior outward, so the retarder is placed toward the interior; in a hot-humid climate the dominant drive is inward, and an interior retarder is counterproductive because it traps inward-driven moisture. {note}
−## The climate zone is the single input that governs above-grade vapor retarder class and placement, and it shall be established before any above-grade retarder is selected. {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. {note}
−## Climate Zone {toc}
+## 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. {note}
−### The climate zone governs the above-grade vapor retarder requirements throughout this standard and shall be obtained from the energy code report or the contract documents.
+## The vapor retarder class for above-grade walls shall be as indicated in the datasheet.
```datasheet
−label: Project Climate Zone (IECC/IRC)
−type: select
−drawing_ref: "energy code compliance report"
+label: Wall Vapor Retarder Class
+type: radio
+derived: "the vapor retarder provisions of [[parameter: adopted-building-code]] for [[parameter: climate-zone]], the wall assembly's exterior continuous insulation ratio, and the hygrothermal analysis where that is the design basis"
options:
− - "Zone 1-2 (hot / hot-humid)"
− - "Zone 3 (warm)"
− - "Zone 4 (mixed, non-marine)"
− - "Marine 4"
− - "Zone 5 (cool)"
− - "Zone 6 (cold)"
− - "Zone 7-8 (very cold / subarctic)"
−default: "Zone 4 (mixed, non-marine)"
+ - "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"
+default: derived
```
−### The Contractor shall obtain the project climate zone from the energy code compliance report; the climate zone governs the above-grade vapor retarder class and placement.
+## 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 [[sync/building-thermal-insulation]] and shall be stated in the contract documents.
−## Moisture Design Analysis {toc}
+## A Class I vapor retarder shall not be installed on the interior side of a frame wall where the vapor retarder provisions of [[parameter: adopted-building-code]] prohibit it for [[parameter: climate-zone]], unless a hygrothermal analysis per ASHRAE 160 demonstrates that the assembly dries under the project design conditions.
−### Where assemblies are unconventional, where interior humidity is elevated, or where the dew-point location is uncertain, a hygrothermal moisture-control analysis removes the guesswork from vapor retarder selection. {note}
+## 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.
−### Where the assembly is unconventional or the building has elevated interior humidity (such as a natatorium, food-processing space, or commercial kitchen), the vapor retarder strategy shall be evaluated by a moisture-control design analysis in accordance with ASHRAE 160.
+## 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. {note}
−# Vapor Retarder Classes and Selection {toc}
+## 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.
−## The IBC and IRC classify above-grade vapor retarders into three classes by their water-vapor permeance measured per ASTM E96, and this classification is the basis for every above-grade selection in this standard. {note}
−## Below-slab vapor barriers are classified on an entirely separate scale (ASTM E1745 Class A, B, C) based on strength and puncture resistance, not permeance, and the two classification systems shall not be cross-applied. {note}
+# Wall Vapor Retarder Position {toc}
−## Above-Grade Vapor Retarder Class {toc}
+## 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. {note}
−### The vapor class is the controlling material decision for an above-grade retarder, because permeance that is too low for the climate traps moisture while permeance that is too high fails to control it. {note}
−### Class I (at or below 0.1 perm) includes polyethylene sheet and foil; Class II (greater than 0.1 to 1.0 perm) includes kraft-faced batt facing and coated membranes; Class III (greater than 1.0 to 10 perm) includes latex paint on gypsum board. {note}
+## The vapor retarder shall be installed at the position in the wall assembly indicated in the datasheet.
−### Above-grade vapor retarders shall be classified by water-vapor permeance determined per ASTM E96, with Class I at or below 0.1 perm, Class II greater than 0.1 and at or below 1.0 perm, and Class III greater than 1.0 and at or below 10 perms.
−
```datasheet
−label: Above-Grade Vapor Retarder Class
+label: Wall Vapor Retarder Position
type: radio
options:
− - "Class I (≤0.1 perm) — polyethylene sheet or foil facer"
− - "Class II (>0.1 to 1.0 perm) — kraft-faced batt facer or coated membrane"
− - "Class III (>1.0 to 10 perm) — latex/vapor-retarder paint on gypsum board"
− - "Variable-permeance (smart) membrane — Class I/II by dry cup, >1 perm by wet cup"
− - "None required (Climate Zone 1-3)"
−default: "Class II (>0.1 to 1.0 perm) — kraft-faced batt facer or coated membrane"
+ - "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"
+default: "Interior face of the framing, directly behind the interior finish"
```
−### Class I retarders shall be used only where specified, because their very low permeance can trap moisture in assemblies that experience a seasonal reversal of vapor drive.
−## Variable-Permeance (Smart) Membranes {toc}
+## 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.
−### A variable-permeance membrane is low-perm when the surrounding air is dry (winter, controlling outward diffusion) and opens up to a higher perm when the air is humid (summer, allowing the assembly to dry inward), which is why the IBC and IRC permit a responsive Class I or II membrane on the interior side in any climate zone. {note}
+## 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 [[parameter: adopted-building-code]] tabulate for [[parameter: climate-zone]], or the position shall be supported by a hygrothermal analysis per ASHRAE 160.
−### Where a variable-permeance (smart) membrane is specified, it shall be a Class I or Class II retarder by dry-cup permeance that also exhibits a water-vapor permeance greater than 1 perm by wet-cup permeance, qualifying it for interior use in any climate zone.
+# Ceiling and Framed Roof Assembly Vapor Retarder {toc}
−# Below-Slab Vapor Barriers {toc}
+## 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. {note}
−## The below-slab vapor barrier is a plastic sheet placed beneath a slab-on-grade to stop water vapor from diffusing up out of the ground, through the slab, and into the building or its floor covering. {note}
−## It is classified to ASTM E1745 by tensile strength and puncture resistance into Class A, B, and C, all three of which share the same maximum permeance of 0.1 perm; the class is therefore a measure of physical durability during installation and concrete placement, not of vapor performance. {note}
−## A thicker, higher-class sheet survives the abuse of rebar chairs, foot traffic, and concrete placement with fewer punctures, which is why higher classes and greater thicknesses are specified where the barrier must endure heavy traffic before the pour. {note}
+## The vapor retarder class for the ceiling plane and for framed roof assemblies with cavity insulation shall be as indicated in the datasheet.
−## ASTM E1745 Class {toc}
−
−### Class A is the most robust (minimum 45 lb/in tensile, 2200 g puncture), Class B is intermediate (30 lb/in, 1700 g), and Class C is the least robust (13.6 lb/in, 475 g); the permeance limit of 0.1 perm is identical for all three. {note}
−### Class A is the common specification for commercial work because the barrier must withstand significant construction traffic and reinforcement loading before the slab is placed. {note}
−
−### The below-slab vapor barrier shall conform to ASTM E1745 and shall be the class specified above for the project.
−
```datasheet
−label: Below-Slab Vapor Barrier — ASTM E1745 Class
+label: Ceiling and Framed Roof Vapor Retarder Class
type: radio
+derived: "the attic ventilation and unvented roof assembly provisions of [[parameter: adopted-building-code]] for [[parameter: climate-zone]], whether the attic or roof assembly is vented, and the hygrothermal analysis where that is the design basis"
options:
− - "Class A — minimum 45 lb/in tensile, 2200 g puncture (commercial; heavy traffic before pour)"
− - "Class B — minimum 30 lb/in tensile, 1700 g puncture (moderate-duty)"
− - "Class C — minimum 13.6 lb/in tensile, 475 g puncture (light residential)"
−default: "Class A — minimum 45 lb/in tensile, 2200 g puncture (commercial; heavy traffic before pour)"
+ - "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"
+default: derived
```
−### The barrier shall have a water-vapor permeance not greater than 0.1 perm, measured per ASTM E96, both before and after the conditioning regimen of ASTM E154.
−## Thickness {toc}
+## 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.
−### The sheet thickness is specified in mils, and although ASTM E1745 classifies by performance rather than thickness, the market correlates the two: a 15-mil sheet is the common commercial Class A choice, while heavy-duty applications use 20 mil and light residential work uses 10 mil. {note}
+## A ceiling vapor retarder shall not be installed below a vented attic where the attic ventilation provisions of [[parameter: adopted-building-code]] rely on the absence of one for [[parameter: climate-zone]].
−### The below-slab vapor barrier shall be not less than the specified nominal thickness, and shall meet the specified ASTM E1745 class regardless of thickness.
+## Where the roof is a membrane roof, the vapor retarder on the roof deck is specified in [[sync/membrane-roofing]], and the retarder in this article shall not be installed in addition to it without a hygrothermal analysis per ASHRAE 160.
−```datasheet
−label: Below-Slab Vapor Barrier — Nominal Thickness
−type: range
−unit: mil
−options:
− min: 10
− max: 20
− setpoints: [10, 15, 20]
−default: 15
−```
+# Vapor Retarder Materials {toc}
−## Material Type {toc}
+## Material Selection {toc}
−### Most below-slab barriers are multi-layer polyolefin or high-density polyethylene plastic sheet (ASTM E1745); a reinforced bituminous membrane (ASTM E1993) is an alternate where its higher puncture resistance is wanted. {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. {note}
−### The below-slab vapor barrier shall be a plastic sheet conforming to ASTM E1745, or a bituminous membrane conforming to ASTM E1993 where specified.
+- 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
+### The vapor retarder material shall be as indicated in the datasheet.
+
```datasheet
−label: Below-Slab Vapor Barrier — Material Type
+label: Vapor Retarder Material
type: radio
options:
− - "Plastic sheet (polyolefin / HDPE) per ASTM E1745 (standard)"
− - "Reinforced bituminous membrane per ASTM E1993"
−default: "Plastic sheet (polyolefin / HDPE) per ASTM E1745 (standard)"
+ - "Polyethylene sheet"
+ - "Reinforced polyethylene sheet"
+ - "Foil-laminate sheet"
+ - "Variable-permeance membrane"
+ - "Vapor retarder coating on gypsum board"
```
−## Placement Relative to Slab and Cushion {toc}
+### 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.
−### Whether the vapor barrier is placed directly beneath the slab or below a granular cushion is a genuine engineering debate, and the right answer depends on the floor covering and on the contractor's ability to manage bleed water. {note}
−### Placing the barrier directly under the slab gives the greatest protection to a moisture-sensitive floor covering and prevents rain, saw-cut slurry, curing water, or cleaning water from being trapped in a fill course beneath it; this is the current ACI 302 recommendation where the slab receives a vapor-sensitive covering. {note}
−### The drawback of direct contact is that the impermeable sheet prevents downward bleed water from escaping, so all bleed water rises to the surface; if it cannot evaporate before finishing, the trapped water can cause surface delaminations, blisters, and increased curling at slab edges. {note}
−### Placing the barrier below a granular cushion (the "blotter" layer) lets the slab bleed and drain downward, reducing curling, but the cushion itself can become a reservoir that traps construction water against the slab underside and re-emits it for months, which is why ACI 302 advises against a blotter beneath slabs that will receive moisture-sensitive flooring. {note}
+### 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 [[parameter: adopted-building-code]] permits a higher index for that location.
−### Where the slab will receive a moisture-sensitive floor covering, adhesive, or coating, the vapor barrier shall be placed in direct contact with the underside of the slab, with no granular cushion between the barrier and the slab.
+## Polyethylene Sheet {toc}
+### Polyethylene sheet shall conform to ASTM D4397 and shall have a nominal thickness not less than that indicated in the datasheet.
+
```datasheet
−label: Below-Slab Vapor Barrier — Placement
−type: radio
+label: Polyethylene Sheet Nominal Thickness
+type: range
+unit: mil
options:
− - "Directly beneath the slab (in contact with slab underside) — ACI 302 recommendation where slab receives moisture-sensitive flooring (standard)"
− - "Below a granular cushion / blotter layer — only where no moisture-sensitive flooring and curling control governs"
−default: "Directly beneath the slab (in contact with slab underside) — ACI 302 recommendation where slab receives moisture-sensitive flooring (standard)"
+ min: 4
+ max: 10
+ setpoints: [4, 6, 8, 10]
+default: 6
```
−### Where the vapor barrier is placed in direct contact with the slab, the Contractor shall manage bleed water and shall not begin finishing operations until surface bleed water has dissipated, to prevent delaminations and blisters.
−### A granular cushion shall not be placed between the vapor barrier and a slab that will receive a moisture-sensitive floor covering.
−# Wall and Ceiling Vapor Retarders {toc}
+### 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. {note}
−## The above-grade vapor retarder is placed within a framed wall or ceiling assembly to limit vapor diffusion through the assembly, and its class and its side of placement are both governed by the climate zone. {note}
−## The governing rule is that the retarder goes on the warm-in-winter side of the insulation in heating-dominated climates, so that interior humidity cannot diffuse outward and condense on the cold sheathing behind the insulation. {note}
−## The IRC and IBC set the class required by climate zone, and this standard records that requirement; the design professional remains responsible for confirming the assembly does not trap moisture given its specific insulation and cladding. {note}
+### 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.
−## Requirement by Climate Zone {toc}
+## Foil-Laminate Sheet {toc}
−### Climate Zones 5, 6, 7, 8, and Marine 4 require a Class I or Class II vapor retarder on the interior side of frame walls, because their long, cold heating seasons drive interior moisture outward where it will condense without a retarder. {note}
−### Climate Zones 1, 2, and 3 do not require an interior vapor retarder, and one is generally counterproductive there because the dominant vapor drive is inward; Zone 4 (non-marine) permits Class I, II, or III. {note}
+### 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.
−### In Climate Zones 5, 6, 7, 8, and Marine 4, a Class I or Class II vapor retarder shall be provided on the interior side of frame walls, except where a variable-permeance membrane or a continuous-insulation ratio permits otherwise per the IRC.
+### 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.
−```datasheet
−label: Above-Grade Vapor Retarder — Requirement by Climate Zone
−type: radio
−options:
− - "Class I or II required on interior side (Zones 5, 6, 7, 8, and Marine 4)"
− - "Class I, II, or III permitted on interior side (Zone 4 non-marine)"
− - "Not required (Zones 1-3); Class III permitted with no special conditions"
−drawing_ref: "energy code compliance report"
−default: "Class I or II required on interior side (Zones 5, 6, 7, 8, and Marine 4)"
−```
−### In Climate Zones 1, 2, and 3, an interior vapor retarder shall not be provided on frame walls except where specifically required by the design professional, because it traps inward-driven moisture in cooling-dominated climates.
+## Variable-Permeance Membrane {toc}
−## Placement Side {toc}
+### 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 [[parameter: adopted-building-code]] set for a responsive vapor retarder.
−### Placing the retarder on the wrong side of the insulation is the most damaging error in above-grade vapor control, because it converts a moisture-control measure into a condensation trap. {note}
+### A variable-permeance membrane shall be installed with the face the manufacturer designates toward the interior, where the manufacturer designates one.
−### The above-grade vapor retarder shall be placed on the warm-in-winter (interior) side of the insulation in heating-dominated climates, unless sufficient exterior continuous insulation keeps the sheathing above the dew point or a variable-permeance membrane is used.
+## Vapor Retarder Coating {toc}
−```datasheet
−label: Above-Grade Vapor Retarder — Placement Side
−type: radio
−options:
− - "Interior side of insulation (warm-in-winter face) — heating-dominated climates (standard zones 4-8)"
− - "Exterior continuous insulation keeps sheathing above dew point; interior Class III permitted"
− - "Variable-permeance membrane on interior side (responsive; any climate zone)"
−default: "Interior side of insulation (warm-in-winter face) — heating-dominated climates (standard zones 4-8)"
−```
−### A vapor retarder shall not be installed on the exterior side of the insulation in a heating-dominated climate where it would trap interior moisture against a cold plane.
+### 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.
−## The retarder may be the integral facing of the cavity batt, a separate polyethylene sheet, a variable-permeance membrane, or a vapor-retarder paint, each appropriate to a different assembly. {note}
+### 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.
−## The above-grade vapor retarder material shall be of the specified class and shall be installed continuously on the specified side of the assembly.
+### The coating shall be applied after the gypsum board joints are finished and before any finish paint, and its application shall be coordinated with [[sync/gypsum-board-assemblies]] and [[sync/interior-painting]].
+### A finish paint applied over a vapor retarder coating shall be one the coating manufacturer identifies as compatible.
+
+# Air Barrier Function of the Vapor Retarder {toc}
+
+## 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. {note}
+
+## The air barrier function of the vapor retarder shall be as indicated in the datasheet.
+
```datasheet
−label: Above-Grade Vapor Retarder — Material
+label: Air Barrier Function of the Vapor Retarder
type: radio
options:
− - "Kraft-faced batt facing (Class II, integral to cavity insulation)"
− - "Polyethylene sheet (Class I, 6-mil, sealed to framing)"
− - "Variable-permeance (smart) membrane (responsive Class I/II)"
− - "Vapor-retarder (Class III) latex paint on gypsum board"
−default: "Kraft-faced batt facing (Class II, integral to cavity insulation)"
+ - "The vapor retarder serves no air barrier function"
+ - "The vapor retarder is sealed as the interior air barrier"
```
−## Where the vapor retarder is the integral facing of cavity insulation, the facing shall face the conditioned space side of the assembly in heating-dominated climates, coordinated with [[sync/building-thermal-insulation]].
−## Avoiding Double Vapor Barriers {toc}
+## 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 [[sync/air-barriers]], and shall be made continuous with the air barrier of every adjoining assembly.
−### Two low-perm layers on opposite faces of an assembly trap any moisture that gets between them with no path to dry in either direction, which is why an assembly shall never be built with a vapor retarder on both sides. {note}
+## 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.
−### The assembly shall not contain a Class I or Class II vapor retarder on both the interior and exterior faces, because a double vapor barrier traps moisture between the two layers with no drying path.
−### Where the exterior face already includes a low-permeance layer (such as foil-faced sheathing or closed-cell spray foam), the interior vapor retarder class shall be reduced or omitted so the assembly can dry inward.
+# Installation {toc}
−# Seams, Laps, and Penetration Sealing {toc}
+## Substrate and Sequence {toc}
−## The field membrane rarely fails; the failures concentrate at laps, at seams, and at penetrations, exactly the locations that are smallest in area and most often rushed. {note}
−## For the below-slab barrier these seals are permanently concealed by the slab, so they must be made correctly the first time; for the above-grade retarder they must be made before the finishes close the wall. {note}
+### 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.
−## Below-Slab Laps and Seams {toc}
+### A sheet retarder installed over wet framing seals the water in with the assembly, and the first heating season moves it to the sheathing. {note}
−### A taped lap of adequate width is what makes the separate sheets of a below-slab barrier behave as one continuous membrane; an untaped or narrow lap is an open seam through which ground vapor bypasses the entire barrier. {note}
+### 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.
−### Below-slab vapor barrier seams shall be lapped not less than 6 in. and sealed continuously with the manufacturer's seam tape or an approved equivalent method, in accordance with ASTM E1643.
+## Sheet Laps and Seams {toc}
+### 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.
+
```datasheet
−label: Below-Slab Vapor Barrier — Minimum Lap Width
−type: select
+label: Minimum Sheet Lap Width
+type: range
unit: in.
options:
− - "6 in. minimum lap, taped (ASTM E1643)"
− - "Per manufacturer's published lap, where greater than 6 in."
−default: "6 in. minimum lap, taped (ASTM E1643)"
+ min: 2
+ max: 12
+ setpoints: [2, 4, 6, 12]
+default: 6
```
−### Seam tape shall be applied to clean, dry sheet so that the seal is continuous and free of voids.
−## Below-Slab Penetration Sealing {toc}
+### 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. {note}
−### Every pipe, conduit, reinforcing bar, and footing that pushes up through the below-slab barrier is a hole in the membrane, and each one must be sealed tight to the penetrating element or the barrier leaks at that point. {note}
+### Laps and seams shall be sealed by the method indicated in the datasheet.
−### Every penetration of the below-slab vapor barrier — pipes, conduits, ducts, reinforcing, and footings — shall be sealed continuously to the barrier with a pre-formed boot or a fitted membrane collar sealed with the manufacturer's tape, in accordance with ASTM E1643.
+```datasheet
+label: Seam Sealing Method
+type: radio
+options:
+ - "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"
+default: manufacturer
+```
+### 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. {note}
+
+### 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.
+
+## Penetrations and Electrical Boxes {toc}
+
+### 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.
+
+### Electrical boxes in the vapor retarder plane shall be treated by the method indicated in the datasheet.
+
```datasheet
−label: Below-Slab Penetration Sealing Method
+label: Electrical Box Treatment
type: radio
options:
− - "Pre-formed pipe boot sealed and taped to barrier at pipe and round penetrations (standard)"
− - "Membrane collar cut, fitted, and taped to penetration per ASTM E1643"
−default: "Pre-formed pipe boot sealed and taped to barrier at pipe and round penetrations (standard)"
+ - "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"
```
−### The barrier shall be sealed to the foundation wall, grade beam, or footing at its perimeter so the vapor control plane is continuous from the slab to the foundation.
−## Above-Grade Seams and Penetrations {toc}
+### 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. {note}
−### The above-grade retarder is only as continuous as its seams and the seals around boxes and pipes, and a torn or unsealed retarder is no retarder at all over that area. {note}
+### 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.
−### Above-grade vapor retarder sheet seams shall be lapped a minimum of 6 in. over a framing member or supported backing and sealed with a compatible tape or sealant.
−### Penetrations of the above-grade vapor retarder for electrical boxes, pipes, and mechanical connections shall be sealed with compatible materials per the manufacturer's instructions.
−### Vapor retarder material that is cut, torn, or punctured during installation shall be repaired before the assembly is closed, lapping the repair at least 6 in. onto sound material.
+## Terminations and Transitions {toc}
−# Installation {toc}
+### 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.
−## Below-Slab Installation {toc}
+### Where the wall vapor retarder meets a ceiling vapor retarder, the two shall be lapped and sealed to each other.
−### A below-slab barrier installed over a sharp or rutted subgrade punctures under the first foot traffic, so the surface it is laid on matters as much as the sheet itself. {note}
+### 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.
−### The subgrade or granular fill receiving the below-slab vapor barrier shall be level, compacted, and free of sharp projections, debris, and standing water before the barrier is placed.
−### The below-slab vapor barrier shall be laid out so that sheets are lapped, taped, and sealed into one continuous membrane, with the barrier turned up and sealed at all perimeter foundations.
−### The Contractor shall keep traffic off the installed barrier to the extent practicable and shall repair any puncture or tear before concrete placement.
−### Concrete shall be placed on the barrier in a manner that does not displace, tear, or puncture it.
+### 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.
−## Above-Grade Installation {toc}
+## Repairs {toc}
−### The above-grade retarder must be installed continuously and sealed at every edge, because gaps at the top plate, bottom plate, and openings are diffusion bypasses just as seams are.
+### 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.
−### The above-grade vapor retarder shall be installed continuously on the specified side of the assembly, lapped and sealed at all seams, and sealed at the top plate, bottom plate, and around all openings.
−### Where a kraft or foil facing serves as the vapor retarder, adjacent batts shall be installed with the facing flanges lapped and stapled to provide a continuous retarder plane.
−### The above-grade vapor retarder shall not be installed over wet framing or wet sheathing.
+### Where the parties disagree whether a repair is adequate, the Engineer of Record shall make the initial determination.
−# Inspection and Testing {toc}
+# Field Quality Control {toc}
−## Below-Slab Pre-Pour Inspection {toc}
+## Inspection Before Concealment {toc}
−### This inspection is the only opportunity to verify the below-slab barrier, because every defect becomes permanently inaccessible the moment concrete is placed; it is a hold point, not a punch-list item. {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. {note}
−### The installed below-slab vapor barrier shall be inspected for continuity, taped laps, sealed penetrations, sealed perimeter, and the absence of unrepaired punctures before concrete is placed.
−### The Engineer or the designated inspector shall accept the below-slab barrier as a hold point before the pour proceeds.
+### 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.
−## Above-Grade Inspection {toc}
+### 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.
−### The above-grade retarder is verified by visual inspection before the wall is closed, confirming the right class is on the right side and that seams and penetrations are sealed. {note}
+### 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.
−### The above-grade vapor retarder shall be inspected for correct class, correct side of placement, continuous seams, and sealed penetrations before the assembly is concealed by gypsum board, cladding, or finishes.
−### Any deficiency found shall be repaired before the assembly is closed.
+### Work concealed without the required inspection shall be uncovered for inspection at the Contractor's expense where the Engineer of Record directs.
# Delivery, Storage, and Handling {toc}
−## Vapor retarder rolls are easily damaged by sunlight, abrasion, and crushing, and a roll torn or degraded in storage carries those defects into the assembly. {note}
+## Vapor retarder materials shall be delivered in the manufacturer's original labeled packaging with the product designation and class legible.
−## Vapor retarder materials shall be delivered in the manufacturer's original, labeled packaging and rolls.
−## Vapor retarder materials shall be stored off the ground, under cover, and protected from prolonged sunlight, mechanical damage, and abrasion until installation.
−## Seam tape and accessories shall be stored within the temperature range specified by the manufacturer so that the adhesive performs as intended.
−## Any roll that is torn, punctured, or UV-degraded in storage shall be repaired or discarded, not installed.
+## Sheet materials shall be stored off the ground, under cover, and protected from sunlight, crushing, and puncture until installed.
+## 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. {note}
+
+## 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.
+
# Warranty {toc}
−## Vapor retarders are typically warranted for material defects, and the Contractor shall provide the manufacturer's standard warranty along with the installation warranty for the work. {note}
+## Installer Warranty {toc}
−## The Contractor shall provide the vapor retarder manufacturer's standard warranty for the products furnished.
+### 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.
```datasheet
−label: Vapor Retarder Manufacturer Warranty
−type: select
+label: Installer Warranty Period
+type: range
unit: years
options:
− - "1 year"
− - "5 years"
− - "Per manufacturer's standard product warranty"
−default: "Per manufacturer's standard product warranty"
+ min: 1
+ max: 5
+ setpoints: [1, 2, 5]
+default: 1
```
−## The Contractor shall warrant the vapor retarder installation against defective seams, laps, and penetration seals for a period of not less than one year from substantial completion, or for the period stated in the contract documents if longer.
−## Any moisture damage to an assembly attributable to a defective vapor retarder seam, lap, or penetration seal, or to a vapor retarder installed on the wrong side of the assembly, shall be corrected at the Contractor's expense.
+
+### 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.
+
+### 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.
+
+## Manufacturer Material Warranty {toc}
+
+### The Contractor shall provide the vapor retarder manufacturer's material warranty for the period indicated in the datasheet.
+
+```datasheet
+label: Manufacturer Material Warranty Period
+type: range
+unit: years
+options:
+ min: 1
+ max: 20
+ setpoints: [1, 5, 10, 15, 20]
+```
+
+### 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.