Insulating a house with 2×4 framing using exterior rigid foam
Planning extensive remodel on a 1961 home. I’m taking interior down to studs and replacing siding/roof/windows, so I also want to take the opportunity to make it as energy efficient as possible.
-Rectangular ranch style with 2×4 trusses running the entire length of the house
-Vented attic with ~3 ft peak height so it’s lowish pitch and shallow eaves
-Exterior walls are 2×4
-Climate Zone 5. Calls for R20 walls and R38 roof but I’m all for going above it 🙂
Planned wall upgrade:
-Batts between 2×4 studs
-2-4” of XPS outside of sheathing
-Metal siding over XPS
-R23-R33 walls seem achievable depending on XPS thickness
Planned roof upgrade:
-Replacing 1/3rd of trusses with ridge beam and rafters for higher ceilings in living area, and leaving the rest as is. Roof decking on cathedral and truss portions will match and be level.
-Since part will be cathedral and part will be truss, my thought is to just make whole thing unvented and go with exterior rigid foam.
-That would mean: batts between the studs, 6-8” of XPS over deck, and vented gap under metal roofing for ice dam prevention (problematic in my hood).
-R43-R53 seems achievable but thick roof since most if above deck.
Both walls and roof keep more than 50% of insulation outside of sheathing.
1) In everyone’s opinion, is striving for R33 walls (4″ of exterior foam) overkill if roof will only be R43-53?
2) The cathedral portion of roof will have plenty of cavity for insulation but I am concerned with existing 2×4 truss section. Is there something better than just putting 4″ between the studs so that I can get more R value inside and not increase the above deck thickness too much?
Then secondary, I am reading so many mixed messages on the order of assembly for this setup. Some sites say vapor barrier on inside, others say none needed because XPS is the barrier. I’m confused.
4) What would be correct order of wall from drywall to metal siding?
5) What would be correct order of roof from drywall to metal roofing surface?
Thanks to some great articles on this site, i’ve managed to find the right setup and now just trying to finalize the details. Thanks for the help.
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