Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Under-Slab Vapor Barriers
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### Class selection shall account for installation risk, traffic during the pour, subgrade condition, and any flooring-manufacturer requirement that exceeds the code minimum.
−### A coarse or angular granular fill, heavy reinforcement, or an aggressive pour sequence all argue for the higher puncture resistance of Class A even where code would permit a lower class. {note}
−
```datasheet
label: ASTM E1745 performance class
…6 unchanged lines
```
+### A coarse or angular granular fill, heavy reinforcement, or an aggressive pour sequence all argue for the higher puncture resistance of Class A even where code would permit a lower class. {note}
+
### The membrane shall meet or exceed the following ASTM E1745 minimum properties for the selected class.
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### The IBC below-grade floor dampproofing provision allows a minimum 6-mil polyethylene sheet or approved equivalent. That sheet is inadequate for flooring applications on two counts: its tested performance falls short of the durability needed to survive the pour, and its permeance is far above the threshold for moisture-sensitive finishes. The 6-mil sheet is a dampproofing minimum, not a vapor-control specification. {note}
−# Materials {toc}
+# Membrane Type {toc}
−## Membrane Type {toc}
+## The membrane shall be one of the following types, selected to meet the required class and permeance.
−### The membrane shall be one of the following types, selected to meet the required class and permeance.
−
−### Three material families serve this scope, and they trade off cost, puncture resistance, and achievable permeance: {note}
−- Single-ply polyethylene sheet (HDPE or LLDPE): a single extruded film. Economical; commonly available at 10-mil through 20-mil nominal thickness. Higher mil grades from major manufacturers are Class A capable.
−- Multi-layer reinforced laminate: a woven polyethylene scrim core laminated between two polyethylene films. The scrim core gives high tensile and puncture resistance, so these products are typically Class A and are the workhorse for commercial slabs.
−- Bituminous sheet per ASTM E1993: an asphalt-based composite sheet that achieves true vapor barrier performance (less than or equal to 0.01 perms). Used where the project demands a true vapor barrier for high-sensitivity occupancies.
−
```datasheet
label: Membrane type
…6 unchanged lines
```
−### The membrane material shall be free of recycled content that would compromise the certified ASTM E1745 properties or the manufacturer's permeance rating.
+## Three material families serve this scope, and they trade off cost, puncture resistance, and achievable permeance: {note}
+- Single-ply polyethylene sheet (HDPE or LLDPE): a single extruded film. Economical; commonly available at 10-mil through 20-mil nominal thickness. Higher mil grades from major manufacturers are Class A capable.
+- Multi-layer reinforced laminate: a woven polyethylene scrim core laminated between two polyethylene films. The scrim core gives high tensile and puncture resistance, so these products are typically Class A and are the workhorse for commercial slabs.
+- Bituminous sheet per ASTM E1993: an asphalt-based composite sheet that achieves true vapor barrier performance (less than or equal to 0.01 perms). Used where the project demands a true vapor barrier for high-sensitivity occupancies.
−## Nominal Thickness {toc}
+## The membrane material shall be free of recycled content that would compromise the certified ASTM E1745 properties or the manufacturer's permeance rating.
−### The membrane nominal thickness shall be as required to meet the specified class and permeance, and not less than the value scheduled.
+# Nominal Thickness {toc}
−### Nominal thickness is not the same as ASTM E1745 class. A "15-mil" sheet is not automatically Class A; class is determined by tested tensile, puncture, and permeance performance, and the manufacturer's certified test report is the only proof. Thicker membranes generally resist puncture better and are preferred where the subgrade is coarse or the pour traffic is heavy, but thickness is selected alongside the class requirement, never as a substitute for it. {note}
+## The membrane nominal thickness shall be as required to meet the specified class and permeance, and not less than the value scheduled.
```datasheet
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```
−### A nominal thickness of 10-mil shall be regarded as a Class C baseline and shall not be specified where Class A performance is required.
+## Nominal thickness is not the same as ASTM E1745 class. A "15-mil" sheet is not automatically Class A; class is determined by tested tensile, puncture, and permeance performance, and the manufacturer's certified test report is the only proof. Thicker membranes generally resist puncture better and are preferred where the subgrade is coarse or the pour traffic is heavy, but thickness is selected alongside the class requirement, never as a substitute for it. {note}
−### A nominal thickness of 15-mil or greater shall be used where Class A performance is required, subject to certified test confirmation.
+## A nominal thickness of 10-mil shall be regarded as a Class C baseline and shall not be specified where Class A performance is required.
−## True Vapor Barrier Configuration {toc}
+## A nominal thickness of 15-mil or greater shall be used where Class A performance is required, subject to certified test confirmation.
−### Where a true vapor barrier is required, the membrane shall be a bituminous sheet per ASTM E1993, or a multi-layer laminate independently certified to a permeance less than or equal to 0.01 perms.
+# True Vapor Barrier Configuration {toc}
−### ASTM E1993 is the product standard for bituminous under-slab vapor barriers and is written around the 0.01-perm threshold. Some heavy multi-layer polyethylene laminates also achieve 0.01 perms; where one is proposed in place of a bituminous sheet, the certified permeance test report is the basis for acceptance. {note}
+## Where a true vapor barrier is required, the membrane shall be a bituminous sheet per ASTM E1993, or a multi-layer laminate independently certified to a permeance less than or equal to 0.01 perms.
```datasheet
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```
−## Accessory Materials {toc}
+## ASTM E1993 is the product standard for bituminous under-slab vapor barriers and is written around the 0.01-perm threshold. Some heavy multi-layer polyethylene laminates also achieve 0.01 perms; where one is proposed in place of a bituminous sheet, the certified permeance test report is the basis for acceptance. {note}
−### Seam tape shall be the pressure-sensitive tape produced or approved by the membrane manufacturer for use with the specified membrane.
+# Accessory Materials {toc}
−### Field-improvised tapes are a leading cause of seam failure. Standard duct tape and generic packaging tape do not bond reliably to polyethylene and lose adhesion in the moist sub-slab environment. Only the manufacturer's project-specific seam tape carries a compatibility and performance warranty for the joint. {note}
+## Seam tape shall be the pressure-sensitive tape produced or approved by the membrane manufacturer for use with the specified membrane.
−### Pipe boots and penetration collars shall be the prefabricated or field-formed components produced or approved by the membrane manufacturer for the specified membrane.
+## Field-improvised tapes are a leading cause of seam failure. Standard duct tape and generic packaging tape do not bond reliably to polyethylene and lose adhesion in the moist sub-slab environment. Only the manufacturer's project-specific seam tape carries a compatibility and performance warranty for the joint. {note}
−### Mastic and sealant used to seal penetrations and terminations shall be compatible with the membrane and approved by the membrane manufacturer.
+## Pipe boots and penetration collars shall be the prefabricated or field-formed components produced or approved by the membrane manufacturer for the specified membrane.
−### Repair patch material shall be the same membrane as the field sheet.
+## Mastic and sealant used to seal penetrations and terminations shall be compatible with the membrane and approved by the membrane manufacturer.
+## Repair patch material shall be the same membrane as the field sheet.
+
# Sub-Base and Placement Position {toc}
## The membrane shall be placed directly beneath the concrete slab, in contact with the underside of the slab, on a prepared sub-base.
+```datasheet
+label: Membrane placement position
+type: radio
+options:
+ - Directly under slab, no blotter (current ACI recommendation)
+ - Under slab with granular cushion below membrane on coarse sub-base
+default: Directly under slab, no blotter (current ACI recommendation)
+```
+
## ACI 302.1R explicitly recommends placing the vapor retarder directly under the slab. This is a deliberate reversal of the older "blotter" method and is the current position for moisture-sensitive applications. {note}
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## Design and compaction of the granular sub-base are outside this scope and are covered by [[sync/slab-on-grade]] and [[sync/site-rough-grading]]; this Standard governs only the condition of that surface where it receives the membrane. Where a granular cushion is used to protect the membrane on a coarse sub-base, a minimum 4 in. of compacted granular material per ACI 302.1R is typical. {note}
−```datasheet
−label: Membrane placement position
−type: radio
−options:
− - Directly under slab, no blotter (current ACI recommendation)
− - Under slab with granular cushion below membrane on coarse sub-base
−default: Directly under slab, no blotter (current ACI recommendation)
−```
−
# Installation {toc}
−## General {toc}
+## The membrane shall be installed in accordance with ASTM E1643 and the manufacturer's printed instructions.
−### The membrane shall be installed in accordance with ASTM E1643 and the manufacturer's printed instructions.
+## The membrane shall be unrolled and positioned so the long dimension of the sheet runs in the direction that minimizes the number of end laps.
−### The membrane shall be unrolled and positioned so the long dimension of the sheet runs in the direction that minimizes the number of end laps. {note}
+## The membrane shall be installed continuously over the entire slab area to be protected, with no gaps.
−### The membrane shall be installed continuously over the entire slab area to be protected, with no gaps.
+## The membrane shall be drawn taut and free of wrinkles and fishmouths before concrete placement, to the extent practical without stretching the sheet beyond its rated elongation.
−### The membrane shall be drawn taut and free of wrinkles and fishmouths before concrete placement, to the extent practical without stretching the sheet beyond its rated elongation. {note}
−
## Laps and Seams {toc}
−### Adjacent membrane sheets shall lap a minimum of 6 in. {note}
+### Adjacent membrane sheets shall lap a minimum of 6 in.
−### ASTM E1643 sets the minimum lap at 6 in. The lap is the most likely path for vapor to bypass the membrane, so the width is a floor, not a target; widen it where the manufacturer's detail or field conditions warrant. {note}
−
```datasheet
label: Minimum seam lap width
…6 unchanged lines
```
−### All laps shall be sealed with the manufacturer's seam tape for vapor barrier applications. {note}
+### ASTM E1643 sets the minimum lap at 6 in. The lap is the most likely path for vapor to bypass the membrane, so the width is a floor, not a target; widen it where the manufacturer's detail or field conditions warrant. {note}
+### All laps shall be sealed with the manufacturer's seam tape for vapor barrier applications.
+
### Sealed (taped) laps are mandatory wherever the membrane functions as a vapor barrier or a Class A/B vapor retarder under moisture-sensitive flooring. Unsealed, unsupported laps are acceptable only for basic below-grade dampproofing, which is outside the moisture-sensitive scope this Standard is written for. {note}
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## Perimeter Termination {toc}
−### The membrane shall be terminated at the slab perimeter so that no continuous moisture path bypasses the membrane at the slab edge. {note}
+### The membrane shall be terminated at the slab perimeter so that no continuous moisture path bypasses the membrane at the slab edge.
### An unsealed perimeter lets soil moisture migrate under the slab edge and around the membrane, defeating the field installation. The termination detail depends on whether the slab abuts a foundation wall, a grade beam, or a thickened edge, and on the below-grade wall dampproofing it must tie into. {note}
### The membrane shall be lapped up and sealed to the foundation wall, grade beam, or footing face as shown.
−### Where the slab edge abuts below-grade wall dampproofing or waterproofing, the membrane termination shall be lapped and sealed to that assembly so the two systems are continuous. {note}
+### Where the slab edge abuts below-grade wall dampproofing or waterproofing, the membrane termination shall be lapped and sealed to that assembly so the two systems are continuous.
−### Failing to tie the under-slab membrane to the wall dampproofing is a common detailing gap; the two assemblies are coordinated so there is no break in moisture control at the wall-to-slab joint. {note}
−
```datasheet
label: Perimeter termination detail
…7 unchanged lines
```
+### Failing to tie the under-slab membrane to the wall dampproofing is a common detailing gap; the two assemblies are coordinated so there is no break in moisture control at the wall-to-slab joint. {note}
+
## Repair {toc}
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## Exposure and Coordination with Concrete Placement {toc}
−### Concrete shall be placed over the membrane within the maximum exposure interval established at the pre-installation conference, after which the membrane shall be re-inspected and repaired before placement. {note}
+### Concrete shall be placed over the membrane within the maximum exposure interval established at the pre-installation conference, after which the membrane shall be re-inspected and repaired before placement.
−### Polyethylene degrades under sustained UV exposure, and wind and construction traffic accumulate damage over time. Fixing a maximum interval keeps the membrane in serviceable condition at the pour; if the schedule slips past it, the membrane is re-inspected rather than assumed sound. {note}
−
```datasheet
label: Maximum membrane exposure before concrete placement
…6 unchanged lines
```
+### Polyethylene degrades under sustained UV exposure, and wind and construction traffic accumulate damage over time. Fixing a maximum interval keeps the membrane in serviceable condition at the pour; if the schedule slips past it, the membrane is re-inspected rather than assumed sound. {note}
+
### Concrete placement shall not damage or displace the membrane; equipment, chutes, and personnel routing shall protect the installed sheet. {note}
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### The under-slab membrane controls vapor from the soil, but the concrete itself releases mixing water as it cures. ASTM F2170 measures the in-place relative humidity inside the slab, which is the test flooring and adhesive manufacturers rely on to confirm the slab is dry enough to receive the finish. A correctly installed vapor barrier shortens the drying time and lets the slab reach the threshold; it does not eliminate the test. {note}
−### The slab relative humidity shall not exceed the threshold required by the flooring or adhesive manufacturer before flooring is installed. {note}
+### The slab relative humidity shall not exceed the threshold required by the flooring or adhesive manufacturer before flooring is installed.
−### A relative humidity of 75% is a common ceiling for resilient flooring, but the controlling value is whatever the flooring or adhesive manufacturer states; some systems require 80% and some require lower. The more stringent of the manufacturer's value and 75% governs unless the manufacturer permits otherwise in writing. {note}
−
```datasheet
label: Maximum slab relative humidity before flooring (ASTM F2170)
…6 unchanged lines
```
−### Relative humidity testing shall not begin until the slab has cured and dried sufficiently for a representative result. {note}
+### A relative humidity of 75% is a common ceiling for resilient flooring, but the controlling value is whatever the flooring or adhesive manufacturer states; some systems require 80% and some require lower. The more stringent of the manufacturer's value and 75% governs unless the manufacturer permits otherwise in writing. {note}
−### A minimum drying period of approximately 60 days is typical for standard water-cement-ratio concrete before relative humidity testing is meaningful, but the actual time varies with the water-cement ratio, slab thickness, and the drying environment. The probes are read after the slab has had a realistic opportunity to dry, not on a fixed calendar date alone. {note}
+### Relative humidity testing shall not begin until the slab has cured and dried sufficiently for a representative result.
```datasheet
…7 unchanged lines
```
+### A minimum drying period of approximately 60 days is typical for standard water-cement-ratio concrete before relative humidity testing is meaningful, but the actual time varies with the water-cement ratio, slab thickness, and the drying environment. The probes are read after the slab has had a realistic opportunity to dry, not on a fixed calendar date alone. {note}
+
### The number and distribution of test locations shall conform to ASTM F2170.
…2 unchanged lines
## Membrane rolls, seam tape, boots, and mastic shall be delivered in the manufacturer's original packaging with labels intact and the product designation legible.
−## Membrane rolls shall be stored off the ground, protected from prolonged sunlight, and protected from puncture and crushing until installed. {note}
+## Membrane rolls shall be stored off the ground, protected from prolonged sunlight, and protected from puncture and crushing until installed.
## Polyethylene and bituminous sheet both degrade under sustained UV exposure, and crushed or punctured rolls yield damaged sheet that is hard to detect once unrolled. {note}
…5 unchanged lines
# Warranty {toc}
−## The membrane manufacturer shall warrant the membrane against defects in material for the period the manufacturer publishes for the specified product. {note}
+## The membrane manufacturer shall warrant the membrane against defects in material for the period the manufacturer publishes for the specified product.
## The under-slab membrane is buried and permanent; it cannot be inspected or replaced over the life of the slab, so the manufacturer's material warranty and the certified test data at submittal are the only assurances of long-term performance. There is no field warranty for the installed assembly beyond the Contractor's workmanship obligations, because the assembly is concealed at completion. {note}
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default: 5
```