You need to build in a thermal break
. No matter how much insulation you install, it's worthless if you do not make that thermal break.
We used a modified version of the double wall method
(kept the original bus walls intact and screwed furring strips to the metal wall covering for additional 1" rigid foam insulation). This gave us a thermal break from the rivets. We screwed the finished wall covering (click-lock laminate wood look flooring
) to the furring strips.
You can always insulate outside your shell. You can add your insulation under the floor (what we did) and add insulation to the exterior of the roof (what we might do later down the road
Our BlueBird came with a dense 2" thick fiberglass insulation. The insulation in our bus (walls and ceiling) is like the insulation that we have found insulating the ovens in household cooking ranges. Apparently not all Birds are like this. We coated the exterior of the roof with Henry's SolarFlex roof coating. It made a huge difference. The rivets still get warm but not blistering. Between the roof ribs and their hundred rivets per rib (okay, it's not quite that many), the clear expanse of metal ceiling stays cool. The metal close to the ribs is warmer. So we have started capping the rib rivets with stepped trim moulding that incorporates an air gap for the rivets (my decor is art deco, hence the stepped trim). Hard to describe but easy to do. And it does work. We only did a few of the ribs in the salon to see if it would work. I don't know how much the temp difference is but it is enough to feel the difference with our hands. We don't own an IR thermometer.
Our floors currently only have 15/32" (1/2") OSB on top of the old incredibly well stuck rubber. A thin 3.8mm thick vinyl flooring
will be installed on top. We live fulltime in our bus in cold winter/hot summer climate.
Learn what a thermal break is and do a little research online to see different ways to create a thermal break. You should find a method that suits you and that you can incorporate into your build. When it comes to converting a bus, you need to think outside the box and look at materials a little differently.