I am building this Spring in CT and I plan on using 1.5″ of 2 lb spray foam on my exterior foundation and 3.5″ of 2 lb spray foam on the exterior walls.
One concern I have is thermal bridging thru the 2×6’s. I plan on using vinyl siding (Cedar Impressions) and was wondering if I should use Dow 1/2″ insulated sheathing between the CDX and siding as a thermal break.
Is this the wrong thing to do, will I be trapping moisture between the spray foam and Dow board?
Do I still use a housewrap if I tape the seams of the Dow board?
Do I have the framer add a 1/2″ of CDX around the window & door openings to bring it flush with the foam board (he will be installing the windows, but not the siding.
Dows website is being redone and only some info is available can anybody help??
Thanks, Bigman
Replies
I see you are into overkill...
For a thermal break with framing, it may be easier to use the 'foam under drywall' method. Seems easier overall, and works well in my experience.
Another way: You could put horizontal strapping on the interior, and have the foamers go level to that. This cuts the thermal briging area to tiny spots, and makes for less labor than above.
On the exterior, you would have to consider how the foam impacts all of your openings and flashing details. Just seems like a bigger challenge on the outside IMO. Flashed properly, I do not think it would create any special moisture problems though.
IMHO, you're worrying way too much....specifically about thermal bridging....use current best practices,i.e. housewrap, adequate wall cavity insulation, seal the top of your conditioned space envelope (either the attic floor or the attic roof, your choice), buy good windows and doors (& foam the shim spaces) and a 90% furnace....spend the money you would have spent combating thermal bridging on something nice in the way of trim or amenities, and be happy, your house will be more energy efficient than ~75% of the housing stock in America.....even if you were sleeping on the walls you wouldn't feel the temp. difference at the studs......