Building Science Puzzles: Wine Room Weirdness—Part 2 – GreenBuildingAdvisor

Building Matters

The building science findings and the repair made to this wine room

This is the second of two posts about a wine cellar that’s part of GBA’s Building Science Puzzles series. The first post, which you can read here, discussed the reasons for the investigation, explained the process, and shared the observations, data, and other findings that were collected. This second post details the answer, or at least a hypothesis about what is going on. There may be additional clues to the puzzle in the comments section of the first post.

Our investigation started with a recurring brown drip track on a wall in a wine cellar. Further investigation found there was a puddle of water on the 6-mil plastic sheet that covered the drywall ceiling of the wine cellar. The top of the ceiling is in a vented attic in this slab-on-grade house in climate zone 4.

A conversation with the construction team

You’ve asked the original project manager if they know why plastic was installed on the ceiling, and it turns out that detail was in the instructions from the wine room HVAC system.

As for the gaps in the insulation, there was no good explanation for that, but there was likely to be a problem whether the insulation work was perfect, ordinary, or poor.

The building science behind the problem

The plastic on the ceiling would be pretty close to the temperature inside the room, with only half an inch of drywall separating it from a room maintained at 57°F.

The vented attic is well connected to the outside air, which in this area of the country (climate zone 4) has high humidity levels for several months each year. Dew points reach into the 70s for several weeks in a typical summer and be above 57°F for much of the warm months.

When humid air contacts a cold…