Nobody knows why these problems occur, even from large companies and professionals ... and it seems nobody is doing any actual testing of different roof systems.
For instance what is the change in temperature on the outside and inside of the sheet materials as the sun hits it? Is the problem that the inside cannot expand with the outside? Or is any expansion bad?
Is the goal to rigidly fix the roof down with long screws or thicker boards, or to use short screws which allow movement? Or use OSB ontop of plywood?
How does the situation differ with cold or warm roofs? Warm roof keeps the inside of the boards at a different temp to the outside so the outside will stretch far more in relation to the inside. Well ventilated cold roof could be better. I also wonder if a vapour barrier is needed in this case, why would it be? Also whilst I am at it, why not just waterproof the underside of the deck so it doesn't rot so quickly, can't take that long.
Nobody knows, nobody is testing, even in large companies. This is quite normal I have noticed, nobody is asking questions.
Anybody who wants to set up all these types of roofs and test them, would do the world a favour.
My take is:
- south facing go for EPMD and reflective paint
- if you walk on it or have a wooden decking abo ve use plywood ensure spacing or the plywood will creak - check for how boat builders prepare plywood
- if you have cold roof see Steve Builder's instructions for cross ventilation I would just use mushrooms though and not his complex venting trenches at the walls
- warm roof seems like a total nightmare, completely opposite to traditional roofs, increases height, creates vapour trap in the dwelling, and unlikely to completely prevent condensation in which case you are in trouble ... cold roof accepts condensation but deals with it like a man. You can also coat the underside with waterproofer to increase life ... but a proper ventilated cold roof is bone dry.
- afaik new regs come into forces this year regarding higher thermal requirments for flat roofs then placing rubber membrane over the top of the joists to prevent thermal bridging to the deck is a no brainer that 5 minutes, just drill the deck through no problem.
- it is in the interest of roofers for your roof to fail after 10 years, and for them to bandy about fancy new ideas especially if they require a lot of work or you can be scared by "regulations" - it's clear that even expensive industry standard roofing contractors create roofs that don't work
I would also add that yesterday I saw some OSB in the road, going up on a roof, and it crumbles in the hand with little pressure, I can't imagine why anyone would use this material for anything. I think people are just repeating the advertising for dirt cheap materials, along with all that stuff about the key for fibreglass, as if plywood was never used in boat building !
Steve Roofer discusses the problem, but even he doesn't know the answer, although his newly cut spacers between the boards helped :
