So we started an exterior remodel today, and found that our roof construction is way more mickey mouse than I thought it was.
Our house has vaulted 2nd floor ceilings through most of the 2nd floor with only a small ventilated attic space, but the majority of the 2nd floor is tongue and groove vaulted ceilings with no attic space above.
I learned today that our roof is simply layers of comp shingle laid on top of the tongue and groove one inch panels. There is no OSB. No air cavity. No insulation. The rafters are BELOW the tongue and groove panels as the rafters are visible from inside (painted). We have already contracted to replace the siding and roof but now I'd like to do a better job. We live in SoCal so we have mind weather but our insulation is horrible and I assume this is a big reason why.
Whats the right way to do this? My contractor suggested laying down OSB first, then polyiso (just one inch?) and then weather barrier and tiles.
If I do this, and the roof then becomes insulated, I should change to an unvented attic at that point?
Also does anyone know what code is likely to require for insulation? I'm reading R25 but that would require 5 layers of polyiso stacked on top of each other and that cant be right? Given each panel is only R5