Soffit Vents On Older Houses With "curved" Ceilings - Roofing/Siding - DIY Home Improvement | DIYChatroom

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Old 02-07-2010, 05:57 PM   #1
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Soffit vents on older houses with "curved" ceilings

Pardon me while I butcher the verbage, but I need some help... I have a home built in 1957 with minimal attic insulation. I had a rdige vent installed with the new roof, and installed round soffit vents because there were none (I have a very small overhang on this colonial).

Went into the attic today to tackle the rafter vents and assess the insulation issues. Because the second floor ceiling is curved, I have to remove all the insulation in the bend to get the foam rafter vent in place. Am I better off with the rafter vents with zero insulation, or place a round soffit in each rafter space leaving the insulation there?

My thinking is thus; because I have a minimal overhang, the soffit vent with allow the soffit to "breath" to ambient conditions, but my ceiling will still have insulation above it.

I'm in the HVAC trade and understand how airflow works, but this really is a pain in the butt.



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Old 02-07-2010, 07:53 PM   #2
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Even though the ceiling and rafters are arched or round, there should still be enough room for your insulation baffle and at leist some insulation. It is hard to picture exactly what you are saying.

As far as a lack of room in your soffit... you could always bypass your soffit vent and go with DCI Smartvent. which gets installed under the first couple of rows of shingles. That way the insulation is not ever gonna block of the flow of air to the ridge. That is assuming that you got your baffles in.


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Old 02-07-2010, 10:33 PM   #3
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You need to vent every rafter bay from soffit to ridge. The foam baffle tend to rip apart from the roof deck nail points. They also require a Windblocker to protect the ends of the insulation from wind-washing at the soffit: For the same money spent on the first of those two, you could use H.D.'s baffle and get 35% more clear air flow: Notice to leave a 1" gap between baffle ends. (Plus they don't burn in a fire as the toxic smoke foam ones).

With a continuous ridge exhaust vent rated NFVA of 18 per ft., you need 9 per ft. of soffit vent on each house side along the soffits at each bay. If using the 4-1/2" round vents (3, they install touching each other and will still not be enough. 12"/4-1/2" = 2.67 x 3 = 8 NFVA per foot. My choice would be continuous soffit venting. (9 per ft.)

Be sure to close off any gable or turtle-back vents: Also any powered attic fans:

Is blown-in loose fill in the sloped ceiling, or fiberglass batt?

Be safe, Gary
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