Hi everyone,

Heard about this awesome website by listening to Martin talk the FHB podcast, what a great depth of knowledge that man has!. Now I have a question that I hope to get an intelligent non biased answer for! I currently am in the middle of a project of retrofitting a portion of my barn in order to create a roughly 6′ x8′ bathroom/shower in a room that’s about 16′ x 24. That all is well and good but like I said it’s….a barn, which means there’s is absolutely zero insulation or finished wall surface and the outside wall is also the ship lap exterior siding.

I am concerned mostly with the possibility of mold growth within the wall cavity as it’s not feasible to remove the siding and add plywood sheathing and a membrane to let the section breathe. How can I achieve a good R-value AND some sort of vapor barrier if my inside finished wall surface will also likely be a pine ship lap board. I keep having to remind myself that “it’s a barn” but I also don’t want to take shortcuts that I will regret later via a mold infestation or something of the like. Any and all advice on how to get this figured out is greatly appreciated!

I’ve tossed up the idea of closed cell spray foam at about 4 inches thick bearing in mind the ceiling also needs to be insulated and finished and cost always comes to mind reminding me yet again of my “it’s just a barn” conundrum. I will stop myself before talking too much and hopefully get some good answers. Thanks in advance’