Moisture barrier & insulation for barn loft
I have a 30 x 40 two story barn that the upstairs loft had been insulated with fiberglass batts and drywalled for a temporary residence. The floor of the loft is 2×8 rough cut joists 16″ center with 5/8 plywood flooring. It had been insulated from below with fiberglass batts that has been damaged by birds and rodents. The loft is now used for storage and I plan a workshop area that would only occasionally be space heated for short periods of time, so I can’t justify putting a huge amount of money into insulation. I want to take out what is left of the fiberglass batts to get rid of the birds and the hidden access for rodents. My major concern is keeping moisture out because between the gravel floor and livestock, it can get quite damp. 2 things I considered are hiring someone to spray foam between the joists from below to provide some insulation and keep out moisture. I assume closed cell, but what would the minimum thickness be.
Or 1″ sheets of foam above the loft flooring, taping the joints and adding osb on top. This would also make the flooring more solid, as it is springy in places. If I go with insulating from above, what would be the best foam board to use and what’s the minimum thickness of the OSB can I use for this sort of sandwich?
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Replies
J. Gaub,
1. You didn't tell us where you live, or anything about your climate, so it's hard to make recommendations about insulation.
2. Closed-cell spray foam is a good product for this application.
3. It's sometimes hard to give advice when the budget is tight. A quality installation is rarely inexpensive.
4. Here's a link to an article I wrote on this topic for the current issue of Fine Homebuilding:
http://www.finehomebuilding.com/design/departments/energy-smart-details/how-to-insulate-a-cold-floor.aspx
Sorry. 5A heating climate
J.,
In climate zone 5, the code calls for a minimum of R-30 insulation in floors.
If you use closed-cell spray foam, that's about 4 3/4 inches. If you use open-cell spray foam, that's a little more than 8 inches.
This is for a storage area that will only be space heated for an occasional work shop project, so i am not really concerned about code. My main concern is moisture to keep the stuff stored upstairs dry. R30 would be great, but not really necessary.( Unless I get kicked out of the house and have to move in - lol)