A very low addition…
We’ve been contracted by a repeat client to build a small dining room addition (11′ x 12′) attached to a contemporary ranch in Maine. Due to very difficult access issues, the addition has to be supported on sonotubes. Bottom of joists (2×10 with fg batts) will only be 2-3 inches over grade.
I’m concerned about moisture migration from ground into joist bays as well as air circulation under the addition. We’re planning to use PT 1/2″ ply with caulked seams on bottom of joists wrapped in hardware cloth. There will be good overhangs on the two eaves walls and none on the gable end. It’s a flat site with mature gardens all around, so pitching the grade isn’t a possibility. Oh, and the homeowner won’t let us use gutters. I’ve shared my concerns about these decisions, but it is what it is. They are good people and I want to do this right for them.
What do you think? Teno barrier applied to bottom of ply to limit moisture upwards? Sealed 3/4″ T&G subfloor to limit moisture migration downwards? Other approaches and/or concerns?
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