Foam insulation on top of Bitumen low-slope roof?
QUESTION: Pros/Cons of spraying foam on top of roof for insulation, then coating with Acrylic or Silicone
Location: Hawaii (warm all year, very high UV, no heating)
Home: Single story 1960’s shallow pitch (2:12) with very low slope enclosed patio (but water does run off — not completely flat – no ponding). No air conditioning (yet).
Roof: ¾” Plywood + 2-ply Bitumen
PROBLEM: Home is HOT due to no insulation over high open beam ceilings
Assumption: We are not going to insulate the inside of the home.
½ of home is shallow drop ceiling and does have R19 fiberglass on top of ceiling (in between ceiling joists).
½ of home is all open beam. Looking up, we are looking at the roof.
Possible consideration for spraying only over the open beam section to reduce cost?
Concern — unsmooth finish. Sounds like the thicker, the higher risk. 2” sounds reasonable… maybe 3”, but certainly not thicker.
Quotes we should have soon:
We are getting a quote – 1.5” SWD Spray foam + SWD or APOC silicone. — Cost ~ $12/ft2 (Person spraying has been supposedly doing this for 15 + years)
I have another person that utilizes sprayers from the mainland and prefers acryclic coatings – ~ $9/ft2
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