How is the ceiling area for a cathedral ceiling measured?
The newest issue of Fine Homebuilding has some information on changes in the IRC and IECC which are of interest to me. One is Code: N1102.1, N1102.2.2 which refers to limitations in size of cathedral ceilings. “The IECC now limits the size of cathedral ceiling to 20% of the insulated ceiling area … The IRC has limited the size of cathedral ceilings to 500 sq. ft.”
Can anyone give me any information on precisely how the area of a cathedral ceiling should be measured. Also – what does the code define as a “cathedral” ceiling – is any sloped ceiling included in this definition?
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What an extraordinary thing to have in your code. Do you know what the thinking behind this is?
I'm looking at page 45 in issue #204 of Fine Homebilding in an article on changes to the code which are meant to improve energy efficiency (Green Yesterday, Code Today). The code involved is the recently released 2009 International Residential Code (IRC) or International Energy Conservation Code (IECC). As far as I can understand it (I have not read the actual text of the Code) it has to do with addressing the issue of poor insulation in cathedral ceilings - they seem to be restricting the allowed area of such ceilings instead of mandating more insulation in them.
That's a shame! Glad I don't work under codes currently.I have built many homes that are entirely cathedral ceilings and no problems with insulation or ice damn issues.I don't know the official definition. it seems to get applied broadly in different venues. To me it means a sloped ceiling, usually with no attic above, tho I know of one that is ceiling only sloped and has living space above on second floor. Some might say it haS TO BE A STEEP PITCH OR THAT IT NEEDS TO HAVE EXPOSED TIMBERS TO BE A TRUE CATHEDRAL, WHILE OTHERS ACCEPT THE TERM FOR A DOUBLE WIDE MOBILE HOME WITH A 1/12 PITCH oOOPS - SOORRY THE capps
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That is funny. A common feature in many tract houses here is to have trussed roofs modified over the living or master bedroom to provide cathedral ceilings. I can't see how it affects their insulation at all.
I guess with a cathedral you don't have an insulated ceiling joist zone and a dead air space in the attic buffering the living space below from the roof/ceiling. All the insulation has to occur right at the ceiling/roof.
But it may also be the "heat rises" issue, where all the heated air goes to the cathedral. Although, if it's that, there should be allowances for radiant heat, I guess.
just guessing tho'
k
edited to add: Now that I re-read your post, I'm guessing the modified truss/cathedrals you're talking about have room for insulation at the truss chord and have a dead air space. So, forget what I posted above in that case. Maybe the reg only applies to true cathedrals with load bearing ridges... who knows.
Or, if it's the heat rises argument, maybe it would apply to your modified truss/cathedral. But then it should apply to 12' ceilings, too.
Edited 5/25/2009 9:07 pm by KFC
Ah, the hardiplank mock-craftsman style tract house with cathedral ceilings and glue-on rock pillars. They would make a stone statue of William Morris weep tears of blood. The insulation level in their roof is the least of their problems.
"But then it should apply to 12' ceilings, too."
That is one of the things that I have thought, also. I'm still wondering if anyone knows how the "code" measures the area of cathedral ceilings. The 500 sq. ft. certainly seems like a very small allowed amount - if that is to be applied to any size house - whether it is area over the floor space below or area of ceiling planes.
I had one in the last house. It was as well insulated as the rest of the house, but the huge air volume, combined with the hot air in the room flowing up above head level, mad it a real bear to heat or cool, and killed the efficiency of the whole house.
I don't have an answer, just re-stating your (interesting) question.
Is the "area of a cathedral ceiling" the square footage from wall to wall under the ceiling,
or,
Is it the combined interior surface areas of the two inclined roof planes?
I can see arguments for either. If you're looking at the insulation in the roof, then it should be the roof planes, but if you're considering the space below which is losing it's heat up into the cathedral, then it should be the rectangle from wall to wall.
Obviously, the inclined roof planes will give a larger number.
I don't have a copy of the latest FHB, nor access to the code itself. Anyone?...
k