Crawl Space Vapor Barriers in Maryland
A crawl space vapor barrier is the foundation of any moisture control strategy — blocking ground evaporation before it can saturate the air, wood, and insulation above. But vapor barriers are only as effective as their installation: gaps, tears, unsealed seams, and missing wall coverage undermine the entire system.
Get a Free Inspection (443) 855-5600What a Vapor Barrier Actually Does
Soil is constantly releasing moisture through evaporation — a process that continues year-round but accelerates during Maryland's wet spring and humid summer. In an unencapsulated crawl space, that moisture evaporates freely into the crawl space air, raising relative humidity to levels that support mold growth, wood decay, and pest activity. A vapor barrier physically covers the soil surface, blocking that evaporation pathway at the source.
The key word is "barrier" — not "sheet." A thin 6-mil poly sheeting laid loosely over the floor is not a vapor barrier in any meaningful sense. It tears, shifts, and allows moisture to escape through overlaps and punctures. An effective vapor barrier is heavy-duty, reinforced, properly sealed at seams, and mechanically fastened to foundation walls.
OBW's Vapor Barrier Specification
- 20-mil reinforced polyethylene — rated for long-term ground contact, puncture-resistant, and dimensionally stable
- Full coverage — liner covers the entire crawl space floor with no gaps around piers, columns, or equipment
- Seam overlaps taped and sealed — all seams lapped a minimum of 12 inches and sealed with compatible tape to eliminate vapor pathways
- Wall termination — barrier runs up all foundation walls and is fastened 6–12 inches above the floor with mechanical fasteners and compatible sealant
- Penetration sealing — all pipes, posts, and structural columns are wrapped and sealed individually
Vapor Barriers in the Context of a Complete System
A vapor barrier addresses ground moisture — the largest single source in most Maryland crawl spaces. But open foundation vents, wall cracks with active water intrusion, and high indoor humidity loads require additional components: vent sealing, drainage, and dehumidification. OBW assesses each crawl space as a system and installs what each situation actually requires. Every installation is backed by our Lifetime Transferable Guarantee.
Ready to solve your crawl space problem?
Family-owned since 1953. Honest, consultative guidance. Lifetime transferable guarantee. MHIC 4247.
Schedule Your Free Inspection (443) 855-5600