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.
1. 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?
2. Is there than any negative affect from applying at least 5 inches of open cell spray foam to the inside
3. 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.