HOME COMFORT: “How Can I Insulate a Cabin Roof From Above?”

• Video Watch Time = 1 1/2 minutes

Question: How can I add insulation to the roof of a 500 square foot cabin without covering the rafters and roof boards you can see inside? My place is in the eastern townships of Quebec, Canada and we’d like to visit sometimes in the winter. We get seriously cold winters with temperatures down below -30ºC (-22ºF).

Answer: Two inches of rigid foam will deliver a surprising amount of real-world insulation, but numerically it’s far lower than the R value required by code. I have a cabin on my property (that’s the roof being built above) and it has 2 inches of extruded poly foam on top of 1 1/2” thick roof boards.  I built it this way for the same reason you have in mind, so I could see the rafters and roof boards from below. The cabin is almost as small as yours, and in practice it doesn’t matter that the insulation is not up to modern standards. It takes a bit more firewood, but it’s not significant because the roof and cabin are so small.

If you were planning to live in the place all the time during winter, then I’d definitely go with more insulation than just 2 inches in your case, but there’s something to keep in mind. The only problem with putting more insulation on top of the roof is that it can make the roof look quite thick from the edges. I’d recommend experimenting with different thicknesses of foam in a small space near the eaves, just to ee how things look before you make up your mind.

Watch a video tutorial I made a while back explaining how I install insulation on top of roofs when I want to retain view of the roof structure underneath.