Best Wall assembly for very likely moisture intrusion
I have a friend that would like to insulate a portion of a large heavy timer framed shop building on their property. The building’s foundation is a series of lock blocks (also know as click blocks I think, and I’m sure it other things as well) on which sits a sort of built up sill plate of laminated 2x material that’s perhaps 8”” tall and 6” deep. The structural posts sit on this with the space between the posts framed out with 2” x 6”. The exterior is board and batten with what appears to be landscape cloth and/or roof underlayment behind it attached to the exterior face of the 2x6s.
The issue is that the foundation blocks stick out past the exterior face of the wall, collecting water which then moves under the wall, occasionally pooling on the interior floor.
My friend would like to insulate this wall as part of turning ~400 ft2 of the -1600 ft2 footprint into a heated wood shop.
anyhow, let’s assume for the sake of argument that stopping the water is not an option at this time (that’s a separate project, no guarantees of success).
The shop is to be heated with a hydronic unit heater served by an existing wood boiler to something like 15C when shop is in use.
I’m thinking 2” of continuous eps on the interior of the wall for the first 2 vertical feet, above which would be rock wool cavity insulation. Wall to be finished with bare plywood, possibly roofing tin over the eps portion. The reasoning is to minimize materials pervious to water, leave a portion of the cavity open to foster air flow, and reduce the thermal bridging of the sill.
is it even worth it to insulate the space at all? Boiler heats the house as well and is oversized to the task.
would the typical interior 6 mil poly vapour barrier still be a good idea? If so, down to the floor or stop at the top of the eps?
Is it worth the trouble of attempting to fashion a sort of air barrier in the stud bay against the back of the board and batten siding?
What about a good continuous air barrier with moderate permeability in place of a true vapour barrier?
Just looking for a reasonably well insulated assembly that will not decrease the longevity of the structure.
I think we’re technically in 6B but it’s pretty damp here, I’d say we’re closer to 6C if there was such a thing.
Thanks for taking the time to read through this.
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