Insulating existing barn with board and batten siding?
Hello,
I have an existing post and beam barn in Massachusetts that my wife and I would like to convert to a workshop/studio space. It’s clad with existing rough cut vertical pine siding to which I plan on adding vertical battens to seal it up better.
I would also like to insulate. Preferably with Icynene to get a tight seal and discourage rodents from nesting in the exterior cavities. The Icynene dealer suggested open cell and said that a weather barrier isn’t necessary(?)
A friend expressed concern about the spray foam insulation and the lack of weather barrier and drainage plain. He seems convinced that the exterior pine siding will rot out with prolonged contact to the spray foam insulation because moisture from the outside will have no way of escaping. In an ideal world we would re-side the barn and add a weather barrier and drainage plane, but that’s beyond our budget.
Our current solution is to add 1″ rigid foam insulation to the interior of the cavities- held in from the exterior siding by about 1/2″ to create a drainage plain within the existing cavity. That would leave about 3″ or so to fill the remainder of the cavity with spray foam.
Does this sound like a good idea? My only concern is that a drainage plain inside the wall will mean moisture sitting on the horizontal members. So far this the best plan we can come up with. Any ideas for better solutions or modifications would be appreciated.
Thanks in advance,
Evan
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Replies
Evan,
Q. "The Icynene dealer suggested open-cell and said that a weather barrier isn't necessary."
A. A water-resistive barrier (WRB) is recommended by building experts for all walls. Moreover, a WRB is required by code for all walls. So your Icynene dealer is wrong.
That said, compromises must sometimes be made when renovating old buildings.
Q. "A friend expressed concern about the spray foam insulation and the lack of weather barrier and drainage plane."
A. Your friend sounds smart.
Q. "He seems convinced that the exterior pine siding will rot out with prolonged contact to the spray foam insulation because moisture from the outside will have no way of escaping. In an ideal world we would re-side the barn and add a weather barrier and drainage plane, but that's beyond our budget."
A. Fortunately, the pine boards are vapor-permeable, and they can dry to the exterior when they get damp. That said, it's not a good idea to subject the boards to conditions under which the back side of the boards are often damp, and the outer face of the boards are often dry. This situation would lead to cupping.
Ideally, you need to create an air gap between the back side of the boards and the next layer toward the interior.
Q. "Our current solution is to add 1 inch rigid foam insulation to the interior of the cavities -- held in from the exterior siding by about 1/2 inch to create a drainage plane within the existing cavity. That would leave about 3 inches or so to fill the remainder of the cavity with spray foam."
A. That sounds like a good plan. Pay attention to airtightness at areas that aren't sealed by the Icynene.
Q. "My only concern is that a drainage plane inside the wall will mean moisture sitting on the horizontal members."
A. I wouldn't worry about that. The pine boards are vapor-permeable and air-leaky. Everything will dry quickly when the sun comes out.