We are building a 2×4 stud steel frame tiny house on wheels.  It shall be built & registered under RVIA standards, however, because it is a house (not a camper) we are also following IRC code compliancies.

1) We need help figuring out our roof.  Here’s the deal: The entire structure must stay under 13’6″ for road legality, therefore our “hot roof” (cathedral ceiling) cannot be too thick. The roof joists sit at a peak of 13’1″, leaving us with five inches to work with before tipping the limit. Climate zones we plan to live in are zones 4 & 5.

2) Our other complication: The kit we are building does not have eaves, as we must also stay within 8’6″ road limit width without needing special permit to tow the home.  We think we will be using 2×4 wood framing to build out very narrow “faux eaves” just to keep water out of the wall assembly.  This is tricky and if anyone has advice on how to protect a house without eaves, bring it! We realize it’s not ideal, but we have to find the best solution possible.

So, here’s our best guess at a proposed roof assembly from the top down: Metal roof > roof underlayment (need recommendations for what to use) > Grace Ice & water shield > polyiso rigid foam board(s) (how many, what thickness? I read climate zone 4 requires R-20, and 5 requires R-25. That means 4″ foam) > zip system 1/2 inch roof sheathing > roxul or rockwool batts between the steel roof joists > tounge + groove pine ceiling (sprayed with cork spray?? someone else suggested this…I’m thinking no because that might create a vapor barrier, which we don’t want with a hot roof, correct?)

We aren’t professional builders, but are students using this opportunity as a chance to learn new skills.  Please keep that in mind if you can help give us answers–we may not be familiar with certain terminology yet. Thank you in advance!!