Below-Slab Vapor Barrier Guide
How to review below-slab vapor barriers for continuity, penetrations, laps, terminations, puncture protection, and coordination with foundations and utilities.
Below-slab vapor barriers reduce vapor migration from the ground into slabs and interior spaces. They are often shown as a note, but their performance depends on continuity at laps, penetrations, footings, pits, grade beams, and utility entries.
The review should follow the barrier as a membrane system, not as a product listed in the specifications.
What to Review
Compare architectural floor assemblies, structural slab details, foundation plans, plumbing sleeves, electrical conduits, elevator pits, sumps, and waterproofing details.
- Specified vapor barrier class, thickness, seams, and tape requirements.
- Lap length, sealant, puncture repair, and protection board requirements.
- Terminations at foundation walls, grade beams, pits, and slab edges.
- Penetrations for utilities, sleeves, drains, sumps, and grounding.
- Sequencing with reinforcement, chairs, granular base, and concrete placement.
Why Continuity Fails
Vapor barriers fail when trades treat them as background material. Unsealed penetrations, torn laps, chair punctures, and missing terminations can defeat the assembly even when the correct product was purchased.
Helonic can help reviewers identify drawing locations where continuity needs a detail before the slab is placed.
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