Vapor/Moisture Barrier between unheated shop and 2nd floor heated space
stevel_mi
| Posted in Energy, Heating & Insulation on
I am insulating, heating and finishing the second floor of a pole barn in northern Michigan. The first floor will not be insulated and has a concrete floor that carries a lot of moisture—a piece of wood left on the floor will become wet in a day and moldy in a few days. My plan is to insulate the walls and the joist space between the first and second floor with Rockwool insulation and the attic with blown cellulose. What vapor and/or moisture barrier should I use between the first floor and second floor? The builder wrapped the exterior with Tyvek before putting up the siding and left plenty behind. Thanks
Replies
15# felt under flooring is what we do on first floors above basements. SOP.
Frankie
Tyvek isn't a vapor barrier by any means. Very vapor open. And things in contact with the wet ground or slab are very different from things many feet above with outdoor air in between. Ie, I don't think your wet slab is very relevant here.
I think the main question is how much moisture is in the first floor. Pole barn sounds very air-leaky so the moisture is only as bad as outdoor air? In which case a vapor barrier isn't going to do much, and since you're in a cold climate, could cause problems if it's on the wrong (outside) side. Assuming the first floor will be at or near outdoor conditions, you want to build the floor the same was as the wall: 1. allow for drying outwards at least (no outer vapor barrier, but the tyvek is ok), 2. don't let indoor air leak into it (interior air barrier - but plywood subfloor can do this if the gaps are tight or taped, ), 3. cellulose is very forgiving of occasional moisture, just dense pack it correctly. mineral wool much less so (it doesn't absorb moisture, which is good for it but not for the framing around it)