Vapor Barrier
Installation
in Maryland

20-mil is the appropriate spec for a basement wall application subject to soil contact and hydrostatic pressure. Thinner 6-mil and 10-mil barriers are sold widely but they puncture during installation and degrade faster under Maryland's clay-loaded soil. OBW specifies 20-mil reinforced polyethylene for wall applications.

Floor applications in conjunction with drainage systems can use lighter material where the drainage tile handles the load. If a contractor is quoting you a 6-mil barrier for your basement walls, ask why — the cost difference between 6-mil and 20-mil is marginal, but the performance difference over a decade in Maryland conditions is not.

No, and confusing the two is how homeowners get sold incomplete solutions. A vapor barrier controls moisture vapor migration through walls and floor — it slows the movement of water molecules through porous concrete. It does not intercept or redirect liquid water that enters through cracks or the cove joint.

Used alone on a wet basement, a vapor barrier will trap water behind it and eventually fail or peel. Properly installed, a vapor barrier works in combination with drainage tile and a sump pump — not as a standalone solution. When a contractor sells you a vapor barrier as your waterproofing solution, they're selling you half a system.

Drainage matting (dimple board) is mechanically fastened to the wall first, creating an air gap that channels any water that gets through the wall down to the drain tile. The vapor barrier is then installed over the matting, sealed at seams with tape, and tucked into the drain tile at the base.

The mechanical fastening pattern matters — tape-only installations eventually peel. OBW mechanically fastens at 12-inch intervals. Every penetration through the barrier — pipes, columns, electrical conduit — is sealed individually. A barrier with one unsealed pipe penetration fails at that point and wicks moisture behind the rest of the installation.

A properly installed 20-mil reinforced barrier in a basement with functioning drainage typically lasts 25+ years. The failure mode is almost never the material itself — it's installation shortcuts: gaps at seams, insufficient mechanical fastening, or installation without drainage so water pressure builds behind the barrier.

OBW's barriers come under the same Lifetime Transferable Guarantee as the waterproofing system. When you sell the house, the guarantee transfers to the next owner. That's a documented disclosure item in Maryland real estate transactions — it's a real asset, not just warranty language.

On walls, yes — it requires removing the drywall to access the foundation wall, similar to other interior waterproofing work. We work to preserve as much of the existing finish as possible. In most cases we remove the bottom 12–18 inches of drywall along the perimeter rather than flood-cutting the full wall — meaningfully less to restore afterward.

On the floor, vapor barrier beneath a floating floor system is standard practice for finished basements. We assess the existing finish and advise on minimum removal scope during inspection. There is no honest way to quote this scope without seeing the basement — an inspector who prices it over the phone has either guessed or intentionally lowballed.