Insulation and WRB advice in California Zone 2 (Also considered Zone 4b)
Hi, we lost our home in a wildfire and are finally rebuilding our hopefully forever home, which is going to be on a tight budget and almost entirely a DIY project consisting of a two story Barndominium type home which will have steel legs and trusses with 2×6 wood wall girts and 2×10 wood roof purlins and an open gable ceiling. Our location is Lake County, CA which used to be considered Zone 4b but is now called Zone 2 according to California anyway. Site specific climate consists of hot dry summers reaching into the low 100’s and mildly cold winters mostly above deep freezing but can dip down to about 25 degrees or so during an extreme cold weather event. Very rarely a dusting of snow, (No snow load) otherwise winters are typically equal parts rain and sunshine. We plan to pull local building permits if that factors in.
Looking for advice on whether our plan for the homes envelope looks good and if the WRB and insulation seems scientifically sound, as well as meeting code requirements. Furthermore, advice on if it looks reasonable for long term efficiency, and comfort.
Here is the itemized plan for enclosing and insulating:
Roof with 2×10 wood purlins:
-Metal roofing (PBR or possibly snap lock standing seam)
-Underlayment
-15/32” Techshield R barrier osb with foil seam tape (WRB)
-1” Polyiso R-Max or 1” Closed cell spray foam (R6)
-7.25” Rockwool Comfortbatt (R30)
-1” Rockwool board (to fill rest of cavity) (R4.2)
-1/2” sheetrock
Walls (Lower 10’): 2×6 Standard Vertical wood framing @ 24” O.C.
-Metal siding
-1” Zip R- Sheathing with tape (1/2 sheathing outside, 1/2 polyiso inside) (R3) (WRB)
-5.5” Rockwool Comfortbatt (R23)
-1/2” Sheetrock
Walls (10’ above): 2×6 Horizontal wood purlin framing @ 24” O.C.
-Metal siding
-1” Polyiso R-Max with foil radiant barrier to the outside with taped foil seams (R6) (WRB)
-5.5” Rockwool Comfortbatt (R23)
-1/2” Sheetrock
Look forward to any specific advice or even general help pointing me in the right direction. Thank you very much.
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Replies
-Metal roofing (PBR or possibly snap lock standing seam)
-Underlayment -> Consider a high-temperature peel-and-stick
-15/32” Techshield R barrier osb with foil seam tape (WRB) -> TechShield is NOT a WRB. The foil facer should face an air gap (usually facing inside the attic space) and that is the side that is taped. If you turn it face up and tape those seams you lose the radiant barrier benefits since you have underlayment directly on top.
-1” Polyiso R-Max or 1” Closed cell spray foam (R6) -> why only 1"? Also, if using radiant barrier TechShield you need an air gap so I would put techshield facing inside attic and put polyiso exterior rigid insulation on the outside of the OSB.
-7.25” Rockwool Comfortbatt (R30) -> consider lower cost and lower carbon alternatives such as fiberglass, cellulose, or wood fiber. You are describing a conditioned (unvented) attic so embers cannot enter in from a soffit vent like a traditional vented attic.
-1” Rockwool board (to fill rest of cavity) (R4.2)
-1/2” sheetrock
I think you need to reconsider the radiant barrier placement. And that will in turn effect your insulation layer (whether interior or exterior).
Thanks for the input. Sure are a lot of facets here to consider. I have since found some good articles on the site regarding insulation, WRB and radiant barriers that am going through and already on my way toward a revised plan. Thanks