I am turning a screen porch into a 4 season room, a lot of windows, minimal walls. I want to foam the ceiling and walls, salesman says I need closed cell foam with a higher R value than open cell. Is he BS’n me. He says closed cell has almost 2x
Rvalue of open. Also the installation is almost 2x as expensive. What to do?
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With all the windows, why bother? Just glue in some styrofoam panels. All your heat will escape through the windows anyway.
The important thing is to air-seal.
You don't say where you are but in any case while I agree mostly with Dan I'd still want good sealing and good insulation in the ceiling to keep summer heat and winter cold. Most heat loss is through the ceiling anyway.
What size rathers do you have? Closed cell will act as a vapor barrier also.
Do some reading/research on the Green Building Advisor website. There are numerous articles dealing with foam, both closed and open cell.
http://www.greenbuildingadvisor.com/
Closed cell = approx R-6.5/inch Open Cell = approx 3.85/inch
Open cell foam is generally significantly less expensive and perfectly acceptable, if you don't need a vapor barrier, and provided you have a large (thick) enough cavity to fill. For a typical attic retrofit, I'll generally offer 7" OC or 4" CC. The OC option is more cost effective.