Water is collecting behind the plastic in a new Kansas basement: should the vapor barrier come out?

The owner described the new house on Reddit's r/Homebuilding forum: the builder insulated the framed walls above grade in the unfinished basement with R-13 fiberglass, covered them with plastic sheeting, and condensation now collects on the inside of the poly. The question is whether the sheeting can come off and drywall go straight on.

Wichita's Sedgwick County is in climate zone 4A, according to the Energy Department-funded OpenEI database. The International Residential Code requires an interior vapor retarder (Class I or II) on frame walls only in zones 5 through 8 and marine zone 4, the Insulation Institute says, and exempts basement walls and below-grade sections. The 2021 and 2024 editions go further: in zone 4 outside the marine strip, a Class I retarder such as sheet poly is listed as not permitted on the interior side unless it is a responsive (smart) membrane, while kraft facing and latex paint are allowed.

The water itself has a known source. Answering a nearly identical case on GreenBuildingAdvisor, editor Martin Holladay wrote that new framing and sheathing often carry a lot of moisture in a house's first year, and sun on the outside wall can push it inward, where it condenses on cool plastic. Damp stud bays, he warned, can grow mold or rot, and his advice was to remove the poly.

Pulling the plastic lets the cavity dry toward the conditioned basement. Before the wall is closed, the studs should be checked with a moisture meter: framing for gypsum board should be below 19 percent moisture content under the PS 20 lumber standard, the Gypsum Association's executive director wrote in Walls & Ceilings. A spot that stays wet after the poly is off points to bulk water from outside, which GBA contributor Dana Dorsett said should be dealt with first.