I own a summer cottage in the northern part of lower Michigan. The place was built for summer use only. As such, the walls have no insulation. I'd like to insulate them so as to make it usable in the winter months. The walls are incredibly simple: Cedar siding on the outside, stud walls (with empty stud cavities), and tongue and groove pine boards on the inside. That's it. No housewrap. No vapor barrier or vapor retarder. I'm concerned that if I use fiberglass bats (i.e. traditional insulation), they will get wet and grow mold. However, I know the spray foam insulation is expensive. And I'm receiving conflicting information as to whether that is water resistant. I'm not looking for a really high R-factor here. Just something that will help to retain some heat, without creating moisture and mold problems and something that is cost-effective. Anyone have any guidance or suggestions to offer?

When you say stud, I assume your are talking about a 2x4 and that isn't going to give you much insulation for a Michigan winter. R11 or 13 is all you'd get and without a Tevec wrap you will see heating bills out of site. Your attic also needs about 10 to 12" of insulation. Certainly adding some insulation will help but the real fix is a mighty big task. I'd look into the cost of removing the siding, beefing up to 2x6 framing, adding a wrap and 6" of faced insulation. If it were drywall I'd tear out the interior but with tongue and groove pine you'd ruin every board trying to remove them and you still would not have a wrap.

When you say stud, I assume your are talking about a 2x4 and that isn't going to give you much insulation for a Michigan winter. R11 or 13 is all you'd get and without a Tevec wrap you will see heating bills out of site. Your attic also needs about 10 to 12" of insulation. Certainly adding some insulation will help but the real fix is a mighty big task. I'd look into the cost of removing the siding, beefing up to 2x6 framing, adding a wrap and 6" of faced insulation. If it were drywall I'd tear out the interior but with tongue and groove pine you'd ruin every board trying to remove them and you still would not have a wrap.

Thanks Ballengerb1. Believe it or not, we have already removed the interior pine boards. Fortunately, there were only a few that could not be removed without damaging them, but the vast majority of the boards were removed without causing damage to them. So, right now, all we see are the 2X4s and the exterior cedar siding. The cedar siding is in excellent condition. There appears to be caulk between the boards, some of which has hardened and fallen out of the gaps. I am reluctant to put up fiberglass bats, without appreciating the risks involved. In other words, I am concerned that if I just roll in the insulation, I am worried about creating moisture and mold problems in the future. I'm not looking for 100% efficiency here (or anything even close to that). I just need a way to insulate the walls to retain SOME of the heat without creating the risk of a water trap and mold problem. Having the walls sprayed with foam insulation is very pricey and I'm looking for something that is more cost-effective. This is just a small cabin in the woods. Not looking to break the bank on it, but also do not want to create more problems for the future. Any suggestions?

I have never tried this but there is a spayable vapor barrier usually used for ceiling. You could try spraying the back side of the siding to create a vapor, water barrier. Air & Vapor Barriers - Grace Construction Products - United States - English (http://www.na.graceconstruction.com/template.cfm?page=/vaporret/vaporret_faqs.html&did=9) When you install the new insulation be sure to install with the face on the heated side of the wall or use a ridgid foam board insualtion like FOAMULAR Rigid Foam Insulation (http://www.owenscorning.com/around/insulation/products/foamular.asp)