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hairlesspony 04-11-2014 05:20 PM

Attic Ventilation with Cathedral Ceiling
First post, be gentle.

I did the math on my roof for my 1400 sq ft house and the 2 whirlybirds I have should be adequate with the 12" x12" intakes along my soft fit. So I haven't really worried about myattic airflow.

However, the other day I was re-running some cable in the attic and realized that the 2nd whirlybird is located just above the start of the 1/4th of the house with the cathedral ceiling. There is a gap in the joists that allows a 3" * 12" (IIRC) space of airflow, but I'm thinking this probably isn't enough. All my calculations for efficient airflow are based on the actual attic (the part I can crawl around in) and not the cathedral ceiling.

My question is, should I add another whirlybird? If yes, will that throw the airflow off?

PatChap 04-11-2014 06:24 PM

Is there a full attic above the cathedral or is it cathedral to the ridge? If its cathedral to the ridge you need ridge vent above that section, to vent each rafter bay separately.

hairlesspony 04-11-2014 07:00 PM

It's cathedral on that part to the rafter. I need a new roof anyway and ridge is going to be my SOP. I'm less concerned about the cathedral as I about the other place since my 1960s North Texas house has ducts in the attic. (Yes they are insulated and sealed with mastic, but still...)

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Gary in WA 04-12-2014 04:57 PM

Any facing/vapor retarders present? Did you figure 1/300 or 1/150 on main attic? How many soffit vents- they should be distributed evenly throughout soffit length.....?

PS. Welcome to the forums!

hairlesspony 04-20-2014 01:58 PM

No vapor barrier. I went back and measured the soffit holes. I have 9 total (2 on one side and 7 on the other) roughly 12" by 12". On the one under eave of the roof is a long vent hole that is about 3' by 1' that runs the length of the roof run and one 12" whirlybird.

I'm not sure what the long vent does since it's long enough to be low enough to draw in air but also high enough to exhaust it, however, I know it won't do both. Ugh.

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Gary in WA 04-22-2014 09:41 PM

A picture would help.... Without a vapor retarder/barrier, figure using the 1/150 math;

Are the holes screened/louvered or just big screen? You should have of soffit vent per foot, to meet the 1/150, same with exhaust- for each side of a gable roof, deduct for any louvers/screens for the NFVA. Figure the whirly as hole size only... and they do have their drawbacks.


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