We have a 2×8 @ 16″ O.C. framed Cathedral Ceiling for a residential house in the downtown Toronto area. We plan on using spray-in insulation with continuous soffit and ridge vents in the roof. Is there any suggestions on baffles on air circulation spaces below the plywood deck and above the spray-in insulation. We need to find pre-manufactured products or techniques
Thanks,
David
Replies
I don't know for sure, but I will bet you someone here will recommend a "hot" roof. A roof without ventillation when you use spray foam.
someone here will recommend a "hot" roof
May be recommended, may even make sense--but my understanding is that it would take Royal Dispensation to get some Toronto BI to sign off on unvented roofs, 'cause that's the way the code is written.
I could be wrong, too--it's happened before.
My bet is on flames to mods to move the thread or kill it so that the "real" discussion can be the same Q in Energy Eff.Occupational hazard of my occupation not being around (sorry Bubba)
I am sure the debates will begin, but. Is there a good reason codes go against hot roofs? Do hot roofs work? Do asphalt shingles bake and lift up on hot roofs?
Is there a good reason codes go against hot roofs?
My understanding of this, is that they did a study in damp-cold Minnesota, and venting 40-50s technology/framed roofs fairly definitively prevented ice dams in the studied area. Some how that was promogulated as model code for everywhere, from the Yukon to the equator or some such.
Once set into code, it's more than passing hard to get muni types to see any other way to operate.
Do hot roofs work? Do asphalt shingles bake and lift up on hot roofs?
Well, down here, all roofs are hot, some are just unvented. I've been checking attic temps in my own house, and it looks like the peak air temp was 143º compared to a peak outside ambient of 99º (and the two peaks are not simultaneous, there was a 141º on a 92º day to muddy up the data). So, it looks like I need to price some cheap thermocouples to actually examine the temperature of the roof structure itself.
I've started looking at this after having a client follow the building science recommendations for our region. No change has been seen so far in the shingles, desipte the dire prognostications of the shingle manufacturers. So nice to go into an attic, and it's not a 30-40º delta-T jsut going up the attic stairs.
But, that was out in the county, too--no fussy city BIs to have to convince, either.Occupational hazard of my occupation not being around (sorry Bubba)
You probably don't need to vent. I believe the IRC (or is it ICC??) recently adopted a new rule allowing unvented roofs as long as an "air impermeable" foam is used to seal the underside of the roof decking. Icynene's web site has some info on this, too. In fact, the company is based in Canada.
TF