Todd Miller - Roofing Expert

Underlayment or Not?

Craig asks:
Hi, I’m considering replacing the roof on my hunting camp with new tin. I was curious what to put under the tin as a underlay. I believe there is tar paper now however someone told me I didn’t need an underlay and could just fasten it directly to to the boards. This camp is an old log style built in the 20’s with a board roof. It is heated by wood stove, and only used 3-4 times per year. Any advice you have would be great.

My answer:
Good question. The potential issue here is that metal conducts cold pretty easily. If I understand your exact construction, this could pose a problem by creating a situation where warm moist air inside the cabin could condense.

I would suggest trying to add a vapor barrier someplace underneath the roof and at the very least I encourage underlayment beneath the roofing. I would suggest one of the newer synthetic underlayments such as RoofAquaGuard or Titanium. There are many others as well.

You may also want to consider a layer of rigid insulation beneath the roofing. Make sure that the roof you choose is suitable and approved by its manufacturer for this type of application.