Field & trade terms
Vapor barrier
A vapor barrier (more precisely, a vapor retarder) is a film or coating that slows the movement of water vapor through a wall, floor or ceiling assembly. Warm humid air always tries to migrate toward the cold side, and if it reaches a surface below its dew point inside the assembly it condenses, wetting insulation and framing. The retarder is placed to keep that vapor from reaching the cold surface, and which side it goes on depends on the climate, so its position is as important as its presence.
Run it with the Photo Gate
Insulation inspection checklist
12 items · 26 photos required
Why it matters
Put a vapor retarder on the wrong side of an assembly and it traps moisture instead of stopping it, quietly rotting framing and killing the R-value of the insulation behind it. It's also easy to compromise: a torn sheet or a seam left open lets vapor bypass the whole plane.
What an inspector looks at
The check is that the retarder is the specified material, on the correct side for the climate, continuous and lapped, and cut in cleanly around boxes and penetrations rather than left gaping. It's confirmed against the insulation and air-sealing details it works with, not on its own.
RTI is photo gated, so the vapor retarder is shot in place before insulation and drywall bury it, with seams, laps and the treatment at penetrations shown while they can still be corrected.
Guides that use it
- How to inspect the building envelopeInspect the envelope as a system (air barrier, water-resistive barrier, flashing, transitions, and sealants) with the continuity and mock-up that make it perform.
- How to inspect insulation before coverInspect insulation and its air and vapor barriers before drywall covers them: coverage, fit, continuity, and the gaps that become thermal and moisture problems.
Standards it's verified against
Checklists that put vapor barrier to work
Free, field-ready checklists, each with the photo every item needs before it can be submitted.
Related terms
- Air barrierA continuous plane of materials that stops air from leaking through the building enclosure, sealed at every joint, seam and penetration.
- FlashingThin sheet material lapped into an assembly to direct water back out at joints, edges and openings before it can get behind the finish.
- Dry-inThe point at which a building is closed to weather: roof, wall barrier and openings sealed enough to keep water out and let interior work start.
- Weep holeA small opening left at the base of a cavity wall or window so water that gets behind the face has a path back out.
- Thermal bridgeA path of high heat conductivity through the building envelope (a stud, slab edge or metal member) that bypasses the insulation and lets heat short-circuit through.
- Backflow preventionA device or assembly that keeps used or contaminated water from reversing back into the potable supply through a cross-connection.
Knowing the term is step one. Proving it is the job.
RTI holds the submit button until every mandatory item is answered and the photos are attached, then chains the record so it can be proven untouched later.
30-day trial · No card required