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Lascaux 06-08-2012 11:11 PM

Continuous Soffit Vent Above Lower Roof Too Hot?
2 Attachment(s)
Reading this:
(Please see image in the subsequent message)

... has me wondering if a continuous soffit vent should NOT be installed in a soffit that is only a few feet above another roof section, like this...
Attachment 52169

The house is in climate zone 5A and faces east. The small roof section under the arrow has a shallow eave, the wall below has a southern exposure, and the area below will receive winter sun when not shaded by the chimney. Is the rising of warm air causing snow melt and ice dams above the eave a problem here? Should I forego a soffit vent in this location? There is a similar situation on the southwest corner. Of course, during the summer, the additional air flow might be useful. Is continuous venting that meets NFA minimums, but covers only three sides of this hip roof, sufficient?

Lascaux 06-08-2012 11:21 PM

Continuous Soffit Vent Above Lower Roof Too Hot?
1 Attachment(s)
Sorry, the image height restrictions got me :huh: ...

Attachment 52170

OldNBroken 06-09-2012 09:53 AM

For that small area, see if the intake from just venting the front of the dormer is sufficient air flow. Pretty sure it will be. Remember, you are venting your attic, not your soffits

Lascaux 06-09-2012 11:16 AM

Continuous Soffit Vent Above Lower Roof Too Hot?
Thanks, OldNBroken. :) NFA calculations indicate that a 2" continuous soffit vent should cover the length of just about all of the available soffit on this hip roof section. I could double up the soffit on the front, but there would be an esthetic cost. Also, this south side has only two short soffit sections. How risky is it to use this soffit space on a southern wall that sits just above another roof section?

OldNBroken 06-09-2012 07:22 PM

Intake air may be a little warmer due to the heat in the shingles below but I don't think it will have much of a negative effect on your draft into the attic.

Gary in WA 06-10-2012 07:54 PM

I would vent all soffits not to have a rafter space/cavity where the wind cannot help move the attic air. An attic with just venting and no wind does little to stop convective loops in the attic, fig.7f,7g: And read the conclusions there.

You could also add:

The front portion double-vented would not effect the side roof, only offset your balanced system. Without vents there, the ice dams would surely form.


Lascaux 06-11-2012 04:57 PM

2 Attachment(s)
Thank you, Gary. I had a little trouble finding "Numerical simulation of buoyancy-driven turbulent ventilation in attic space under winter conditions" from the URL you provided, but it was worth it.

Here is my plan:
Attachment 52312

Here is what the roof looked like just before I bought the house in early Spring. Mind you, the house was unheated the entire winter. :eek:
Attachment 52311

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