Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Vapor Retarders
…19 unchanged lines
## The air barrier scope is covered by [[sync/air-barriers]] and is referenced, not duplicated, here. {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]]. {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]].
## 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.
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### 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}
+### 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).
+
```datasheet
label: Installer Qualification Basis
…5 unchanged lines
```
−### 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).
−
## Pre-Placement Inspection {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. {note}
+### 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.
```datasheet
…24 unchanged lines
## Climate Zone {toc}
−### 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. {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.
```datasheet
…30 unchanged lines
### 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}
+### 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
…7 unchanged lines
default: "Class II (>0.1 to 1.0 perm) — kraft-faced batt facer or coated membrane"
```
−
−### 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.
### 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.
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### 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
…5 unchanged lines
default: "Class A — minimum 45 lb/in tensile, 2200 g puncture (commercial; heavy traffic before pour)"
```
−
−### The below-slab vapor barrier shall conform to ASTM E1745 and shall be the class specified above for the project.
### 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.
…2 unchanged lines
### 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}
+### 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.
+
```datasheet
label: Below-Slab Vapor Barrier — Nominal Thickness
…7 unchanged lines
```
−### 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.
−
## Material Type {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}
+### The below-slab vapor barrier shall be a plastic sheet conforming to ASTM E1745, or a bituminous membrane conforming to ASTM E1993 where specified.
+
```datasheet
label: Below-Slab Vapor Barrier — Material Type
…5 unchanged lines
```
−### The below-slab vapor barrier shall be a plastic sheet conforming to ASTM E1745, or a bituminous membrane conforming to ASTM E1993 where specified.
−
## Placement Relative to Slab and Cushion {toc}
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### 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}
+### 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.
+
```datasheet
label: Below-Slab Vapor Barrier — Placement
…4 unchanged lines
default: "Directly beneath the slab (in contact with slab underside) — ACI 302 recommendation where slab receives moisture-sensitive flooring (standard)"
```
−
−### 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.
### 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.
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### 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}
+### 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.
+
```datasheet
label: Above-Grade Vapor Retarder — Requirement by Climate Zone
…6 unchanged lines
default: "Class I or II required on interior side (Zones 5, 6, 7, 8, and Marine 4)"
```
−
−### 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.
### 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.
…2 unchanged lines
### 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}
+### 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.
+
```datasheet
label: Above-Grade Vapor Retarder — Placement Side
…5 unchanged lines
default: "Interior side of insulation (warm-in-winter face) — heating-dominated climates (standard zones 4-8)"
```
−
−### 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.
### 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.
−## Material {toc}
+## 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 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 above-grade vapor retarder material shall be of the specified class and shall be installed continuously on the specified side of the assembly.
```datasheet
…7 unchanged lines
default: "Kraft-faced batt facing (Class II, integral to cavity insulation)"
```
+## 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]].
−### The above-grade vapor retarder material shall be of the specified class and shall be installed continuously on the specified side of the assembly.
−### 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}
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### 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}
+### 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.
+
```datasheet
label: Below-Slab Vapor Barrier — Minimum Lap Width
…5 unchanged lines
default: "6 in. minimum lap, taped (ASTM E1643)"
```
−
−### 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.
### Seam tape shall be applied to clean, dry sheet so that the seal is continuous and free of voids.
…2 unchanged lines
### 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}
+### 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: Below-Slab Penetration Sealing Method
…4 unchanged lines
default: "Pre-formed pipe boot sealed and taped to barrier at pipe and round penetrations (standard)"
```
−
−### 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.
### 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.
…19 unchanged lines
## Above-Grade Installation {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. {note}
+### 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.
### 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.
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## 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}
+## The Contractor shall provide the vapor retarder manufacturer's standard warranty for the products furnished.
+
```datasheet
label: Vapor Retarder Manufacturer Warranty
…6 unchanged lines
default: "Per manufacturer's standard product warranty"
```
−
−## 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 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.