We chose to go with Roxul for a few reasons. One, the quality is superior compared to fiberglass batting as it will not slump or lose R-value if it gets wet. Secondly, Roxul does not burn or off gas during a fire. In fact, despite not being marketed as a fireproof insulation we have heard of people using Roxul to insulate around chimney pipes. I’m not advising that anyone use it for any application the company doesn’t recommend, however, I can tell you that I tested Roxul with a blow torch and it would melt at extreme temperature rather than burn. Roxul is also much easier to install than cutting foam board to fit in between 16″ on center studs.
The other option which is gaining popularity in the Tiny House community is hiring a company to spray foam the walls. The big advantages with spray foam is a higher R-value and the addition of structural stability. However, we decided against the spray foam option because we were concerned with the potential for off gassing. Foam tends to off gas more the newer it is, decreasing over time. Foam board purchased in store has probably off gassed most of its volatile chemicals by the time it is purchased. Spray foam is actually off gassing at a much higher rate than foam board because it is applied directly to the house. A major deterrent to using spray foam was reading several stories online of people having reactions to spray foam installed in their new house, especially when it was applied improperly.
In this video I cover some of the basics of installing our Roxul insulation and talk about why we used 3″ foam board in a few select areas instead.