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Posted: Apr 21, 2009 01:10 PM	Unvented attic is okay, cathedral ceiling is not? I’ve already posted the background under “Need professional stamp in WA” in the Insulation/Energy forum. Basically, I designed and built a small home with an unvented attic. I didn’t know that Washington didn’t allow unvented SPF attics (I don’t know why) until the framing inspector showed up and I told him I was going to use SPF under the roof deck. I made a request to use SPF foam on an unvented roof and it was denied. However, IRC 806.4 was just recently adopted in Washington. My AHJ agreed to take another look at my request for an alternative method/material (since 806.4 doesn’t come into effect until 2010 in Washington). My second floor is ICF kneewalls supporting 2x8 rafters on a 14:12 roof. The span is only 16 feet and the area is mainly two bedrooms. The roof is up, the shingles are on, and there is no provision for ventilation. Rafter collar ties at 10 foot create the bedroom ceilings, creating a tiny attic/HVAC chase about 8’ wide with 4’ headroom. Between the ceiling and the kneewall (approx. 8’) is a cathedral ceiling sloping at about 45 degrees. The ALJ agrees that the IRC allows an unvented attic, but the IRC doesn’t say anything about a cathedralized ceiling. He is concerned about a complete fill in the rafter bays (in order to get R30 insulation). The only code that addresses cathedralized ceilings is the Washington Energy Code, which addresses cathedralized ceilings under its provisions for vented roof assemblies. Therefore the AHJ “reasons,” the only cathedralized ceilings allowed in Washington are vented. My area SPF representative explained that air gaps and ventilation would serve no purpose, but that didn’t seem to effect the AHJ. I couldn’t get an answer as to the purpose of an air gap, other than it was allegedly necessary to meet code (from which I’m attempting to get a variance). It’s as if the fact that I’m petitioning for an alternative to the code doesn’t seem to relieve me of having to meet code. Has anybody had any problem with an unvented cathedral ceiling not being allowed under IRC 806.4? If I call the area between the kneewall and the ceiling a “sloped wall” instead of a cathedral ceiling, does it need to be ventilated when using SPF insulation? Anybody have any ideas? Mark
mason Posted: Apr 21, 2009 09:11 PM	I know it was the intent of the authors of the code change allowing unvented attics that it would also apply to cathedral ceilings. This may require another inquiry to ICC staff for their opinion. It takes about 3 weeks to get an answer, but I will post it when it comes. The ICC staff opinion may be sufficient for your local code official.
Posted: Apr 22, 2009 12:41 PM	Thanks. I already have an ICC opinion letter issued to Demilec in 2006 which re-states the R806.4 requirements for "unventilated conditioned attic spaces", but that wasn't obvious enough for my AHJ. Can I request an ICC opinion directly? Three weeks will make my project stalled for 3 months over this issue. Mark
mason Posted: Apr 22, 2009 02:11 PM	Yes, you can send an inquiry to ICC staff if you are a member. It only costs $100 per year. But my last inquiry took 3 weeks to get to me. Perhaps if you expressed the urgency of the request, it would come sooner.

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Posted: Apr 21, 2009 01:10 PM

Unvented attic is okay, cathedral ceiling is not?

I’ve already posted the background under “Need professional stamp in WA” in the Insulation/Energy forum. Basically, I designed and built a small home with an unvented attic. I didn’t know that Washington didn’t allow unvented SPF attics (I don’t know why) until the framing inspector showed up and I told him I was going to use SPF under the roof deck.

I made a request to use SPF foam on an unvented roof and it was denied. However, IRC 806.4 was just recently adopted in Washington. My AHJ agreed to take another look at my request for an alternative method/material (since 806.4 doesn’t come into effect until 2010 in Washington).

My second floor is ICF kneewalls supporting 2x8 rafters on a 14:12 roof. The span is only 16 feet and the area is mainly two bedrooms. The roof is up, the shingles are on, and there is no provision for ventilation. Rafter collar ties at 10 foot create the bedroom ceilings, creating a tiny attic/HVAC chase about 8’ wide with 4’ headroom. Between the ceiling and the kneewall (approx. 8’) is a cathedral ceiling sloping at about 45 degrees.

The ALJ agrees that the IRC allows an unvented attic, but the IRC doesn’t say anything about a cathedralized ceiling. He is concerned about a complete fill in the rafter bays (in order to get R30 insulation). The only code that addresses cathedralized ceilings is the Washington Energy Code, which addresses cathedralized ceilings under its provisions for vented roof assemblies. Therefore the AHJ “reasons,” the only cathedralized ceilings allowed in Washington are vented.

My area SPF representative explained that air gaps and ventilation would serve no purpose, but that didn’t seem to effect the AHJ. I couldn’t get an answer as to the purpose of an air gap, other than it was allegedly necessary to meet code (from which I’m attempting to get a variance). It’s as if the fact that I’m petitioning for an alternative to the code doesn’t seem to relieve me of having to meet code.

Has anybody had any problem with an unvented cathedral ceiling not being allowed under IRC 806.4? If I call the area between the kneewall and the ceiling a “sloped wall” instead of a cathedral ceiling, does it need to be ventilated when using SPF insulation? Anybody have any ideas?

Mark

mason

Posted: Apr 21, 2009 09:11 PM

I know it was the intent of the authors of the code change allowing unvented attics that it would also apply to cathedral ceilings. This may require another inquiry to ICC staff for their opinion. It takes about 3 weeks to get an answer, but I will post it when it comes. The ICC staff opinion may be sufficient for your local code official.

Posted: Apr 22, 2009 12:41 PM

Thanks. I already have an ICC opinion letter issued to Demilec in 2006 which re-states the R806.4 requirements for "unventilated conditioned attic spaces", but that wasn't obvious enough for my AHJ. Can I request an ICC opinion directly? Three weeks will make my project stalled for 3 months over this issue.

Mark

mason

Posted: Apr 22, 2009 02:11 PM

Yes, you can send an inquiry to ICC staff if you are a member. It only costs $100 per year. But my last inquiry took 3 weeks to get to me. Perhaps if you expressed the urgency of the request, it would come sooner.

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