Extending R-value for cathedral ceiling

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But a 2000 ft^2 R20 roof in a 10,000 DD climate will leak 24 million Btu/year, vs 17 million at R28.
Nick
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Chris wrote:

Fwiw ... R20 conductance is .050 ... 95% efficient, and R28 conductance is .036 ... 96.4% efficient or not much of a difference. And you didn't say but just in case, a ridge vent is the perfect partner for that raft-R-mate (although I would think if the fiberglass is installed carefully the raft-R-mate should not be required). And of course a completely sealed vapor barrier.
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Well that's bizarre ... a cross posting to the same group :-)
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Chris wrote:

With a cathedral ceiling you get one chance to do it right. Put in the max. Stuff in 6" of fiberglass then add as much foam below as you can afford, then add a bit more. I'm in Manitoba, Hydro is recommending R50 now. I put in R60 two years ago. Yes R-Six-Zero.
http://www.mts.net/~lmlod/Cabinfront6.jpg
Temps. around here drop below -40 Deg F. in the winter. With a good fire going in the wood stove the inside temp. near the ceiling peak is probably 80 or 90 deg. F. even with a fan going. A lot of heat to keep snow off the roof.
As for economy and the 95% - 96% boys, where were they years ago when R12 was enough, then R20, R40.
The cost of heat is only going to go up. The bean counters will whine today because "You won't get the return for your money" then tomorrow they will cry "It costs so much to heat, put in more insulation". In reality that bunch doesn't know their ass from a hole in the ground.
If you are building to sell and make a quick buck then go bean counter minimum, otherwise think 20 years down the road. If not for yourself then for your kids if you want them to be able to afford the place.
Lots of ventilation. I put in metal ridge vent right across all three sections.
One added bonus of the metal ridge vent is that birds don't like to land on the things. they stay away from my roof and crap all over my neighbors roof (ridge vent covered with a shingles) Seagulls, crows etc. the stuff covers half the top of his roof and hardly a drop on mine .
By the way I built that place, I hired out the foundation, shingles and HVAC, the rest I did with help from family and friends, not a fricken bean counter among them. :) :) :) and as they say "Put my money where my mouth is".
LdB
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How strange. Why would the ceiling be so hot with a ceiling fan going? Is the stove red hot, with no insulation in the house walls? :-)
You want lots of R1/inch snow on the roof, no?
How can it melt with that 2" air gap?
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Nick, you seem to have no experience heating a house in a cold climate. of course the heat rushes to the peak of his vault! ever heated a house with a wood space heater? an air space alone won't stop snowmelt either. that one has been proven time and again.
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marson wrote:

Don't bother Nick. He's busy trying to solve some partial differential equations to calculate how hot it theoretically should get at the top of a vaulted ceiling, instead of actually having one and knowing it from experience..
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Wrong.
Sure. Ever studied basic physics?
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

as a matter of fact i have...but what's your point? you were arguing that it shouldn't get hot up there by your calculations.
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