I plan to build a climate-controlled garage in North Texas, near the Red river. I want to achieve R-30 in the walls and R-40 in the ceiling. The HVAC air handler and all ducts will be within the climate-controlled space. Exterior walls and roof will be finished with steel sheet panels.
- Will it be effective to sheath the building with foil-faced OSB (foil on the outside), then place 2 x 4 stringers flat on the outside, followed by the steel sheet on top of the stringers; achieving a 1-1/2-inch air space between siding and sheathing? Is there benefit to increasing the air gap from 1-1/2 to 3 inches?
- Is there than any negative affect from applying at least 5 inches of open cell spray foam to the inside?
- Radiant barrier house wrap; what and where? To my knowledge, Tyvek is not a radiant barrier. The foil faced OSB is a radiant barrier, do you recommend redundant radiant barriers? If so, should there be a separate air gap for each barrier? My understanding is that placing anything in the air gap between the inside roof surface and the reflective radiant barrier is counterproductive.
- Using the foil faced OSB with an air gap as your described will be very effective and adding 1-1/2 inches of air gap would add 1.5 R-Value.
- I would caution you about using closed cell spray foam – many people are starting to see moisture damage since it is closed cell and does not allow moisture to pass through it. I also recommend a radiant barrier house wrap.
- Any RIMA-I member can help you. There is no need for a second radiant barrier, only as a house wrap.