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Old 07-18-2009, 10:02 AM   #1
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Newbie: Soffit NFA calculation + what material for vent?


We have a 1950s ranch house that is T-shaped. We need a new roof because the shingles are shot, there is no ice-and-water shield, and this winter resulted in magnificent ice dams with stained ceilings in every room. We'd appreciate your advice.

Reading the posts, I know that we need as much ventilation as possible, so the plan is to put as much 18" NFA vent at the ridge as possible, and at least the same amount of x" NFA venting at the soffits.

The house is roughly 2,700 sf. The maximum amount of 18" NFA ridge vent we can put in is 99 lf. That is more than double the minimum required.

The problem is that because of three gables (with large louvered non-powered vents), the available soffit area is only 138 lf. What do we use to provide at least twice the amount of venting at the eaves?

One of us flat out refuses to have any slots cut into the decking, or at the top of the fascia board, or at the eaves, so there are quite a few products rated at 9" NFA that we cannot use.

Have you got any suggestions?

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Old 07-18-2009, 12:51 PM   #2
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Newbie: Soffit NFA calculation + what material for vent?


So, one of you wants to have Intake Ventilation without having to cut in the necessary intake vent portals?

Try the GAF/ELK for what is known as a Solar Intake Booster.

I never used it, nor even seen it, but it may fit your needs.

I use Smart Vent on all sorts of Ranch Houses with very satisfying results and it gets installed on about 50% of the homes we work on with success and no problems since I first started installing it in 2001.

Ed

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Old 07-18-2009, 04:13 PM   #3
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Newbie: Soffit NFA calculation + what material for vent?


Ed,

Thanks for answering.

Smart Vent is what one of us wanted, but the other nixed the idea of putting any further penetrations in the roof. Thanks to what I read here, though, we will get Shingle Vent II for the ridges instead of Cobra rolled padding. You win some, you lose some.

The soffits are solid wood, except for a few palm-sized eave vents that are not only also screened, but are covered by soffit cover that is not necessarily perforated where the vents are. No ventilation to speak of, in other words.

A contractor who came by this morning (after my first post) suggested tearing out all the soffits and installing perforated soffit covers in their place. That ought certainly be a lot of intake, but is it enough?

Is it even a good solution?
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Old 07-18-2009, 06:22 PM   #4
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Newbie: Soffit NFA calculation + what material for vent?


contractor who came by this morning (after my first post) suggested tearing out all the soffits and installing perforated soffit covers in their place. That ought certainly be a lot of intake, but is it enough

Should be, in fact it is a good option!!!
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Old 07-19-2009, 05:04 PM   #5
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Newbie: Soffit NFA calculation + what material for vent?


Make sure that all of the soffit wood is removed, because the amount of air going through depends upon there being an opening beyond the lanced or perforated soffit panels.

Most of the lanced or perforated soffit panels are rated from 6" to 9" of NFVA per Square Foot of the vented panels installed.

I usually recommend 100% vented panels along the underside of the eave soffits for as much Intake Ventilation as possible.

Ed
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Old 07-19-2009, 06:43 PM   #6
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Newbie: Soffit NFA calculation + what material for vent?


Thank you both. We'll make sure all soffit wood is removed, and that all the insulation is raked back and stops where the soffit starts (the soffits are 12", 18", and 28" wide respectively).

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