poly sheeting in stand alone garage ceiling?
stolzberg
| Posted in General Discussion on
I’m planning to insulate and air seal a stand alone 20′ x 22′ garage for a workshop in Northwest Massachusetts. It has 2×4 walls with shiplap siding (no other sheathing). I have surplus rigid foam polyiso sheets that I was going to use to insulate walls and lay down across the floor of the attic to insulate the space below, wondering if I should lay plastic sheeting across the board floor first and tape seams and to top plates to air seal. I’m planning to heat to 40s in winter, a little higher when I’m out there working, and may use a window AC unit in summers if hot in there. Would poly sheeting cause any problematic condensation?
Replies
Why not install the rigid foam to bottom of the truss (not sure what thickness you have), perpendicular orientation to the truss? If you did this and taped/spray foamed the joints and gaps, then this would act as your vapor barrier. Then you could add insulation on the attic side too.
With a layer of poly on the floor, with foam boards layed on top, you might get some condensation on top when running the air conditioner.
this would happen from air that bypasses the foam board. (like around the edges)
It is possible such condensation would evaporate when things warm up, but perhaps not. Liquid water could run under the boards a bit and then find it hard to escape.
Poly sheeting, also known as polyethylene sheeting, is a type of plastic sheeting that is often used for construction and DIY projects. It can be used in a stand-alone garage ceiling as a vapor barrier to prevent moisture from penetrating the insulation and causing mold or mildew growth. It can also be used as a temporary cover for a damaged ceiling. However, poly sheeting is not recommended as a permanent solution for a garage ceiling as it is not fire resistant and can be easily punctured or torn.