I just bought a new house and it has a detached 20x20’ garage that gets to around 120F (49C) in the summer. I have a quiver of beloveds that I have stored inside my air conditioned apartments for years but now that I have this detached garage I want to keep all my boards out there.
Issue: there’s an age-old fear around delamination associated with exposing your boards to heat. "never leave your board in your car, never leave your tinted board out in the sun etc. etc… My understanding of that rationale is that the heat will cause delamination via uneven thermal expansion of either the air inside the fiberglass shell, or the polyurethane foam itself and the glass/resin. By uneven (and this is where it gets slightly technical) I mean the thermal expansion coefficient of the foam/air is different than the resin/fiberglass so one gets “bigger” than the other and separates and you get delamination.
Question: What is the maximum temperature at which a PU board can be reasonably stored without concern for delamination via thermal expansion? How hot do your garages get that you store your boards in? Think I should keep my boards inside my house during the hot summer months (and piss off my wife) or should I just leave em out in the garage and call it good?
I’ve stored my boards in detached garages for years. Find the coolest wall, (no direct sun) set up racks to store your boards horizontally, to allow even air circulation. Use a soft three point support system, to support each board. You should be fine, with a setup like that. Don’t store the boards too high, and consider placing some screened vents, in the upper corners of the garage. Perhaps some screened vents down low, to bring in cooler air. Natural convection, inside the garage, will keep heat buildup to a minimum.
there is a lot to be said for ventilation and insulation. Install an attic fan to clear the hot air out. and install some fiberglass insulation to the underside of the roof sheating, between the rafters. No thicker than the rafter. Then cover that with the silver radiant barrier.
I’ve always felt better with a board in a bag, especially if the bag has reflective siding on it. My understanding is that throughout the night, the board/bag will cool down. Then the bag acts as an insulator, keeping the board cool throughout the warmer parts of the day. But I could just be talking out my a**…
There is really no thermal expansion of poly foam under about 150F, EPS does expand at much lower temps since it’s closed-cell. Hollow boards will expand faster than EPS and at lower temps (gases expand at higher rates and lower temps than solids). Heat-related delams on poly boards occur when there is a pocket of air between the foam and glass (like a small heel dent where the glass has lost bond to the foam). The expanding air if continuously heated will start peeling more of the bond between foam and glass as the delam bubble grows larger.
So to answer your question, if you don’t have any air pockets under the glass 120F ambient (not solar load) is about the safe max for poly boards. EPS and hollow is much lower even if you have a vent. Most vents can flow only 500 ml/min and if heating is rapid this isn’t enough. Many EPS boards have lots of air pockets in the tail where foam has melted during exotherm on fin box installs and vents won’t help this. In any case, just don’t throw the boards up in the rafters for months or years (like me), check them periodically.
Wow thanks a bunch everyone - awesome technical insight here from both a construction/design perspective as well as chemical/physical/material. Much appreciated - hope this conversations helps others!