What is a good way to install soffit vents here? (see pics)

Old 03-09-14, 03:14 PM
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What is a good way to install soffit vents here? (see pics)

I've been planning to fix my 140 degree attic problem for 3 years now. My a/c is being overtaxed and I have a couple of months more to figure it out. Summer is approaching and I have to get this going now. I gutted my attic and can get down and dirty if needed.

- summer heat is 100 F for 3 to 4 months
- a/c duct work is in the attic
- ridge vent is installed.
- planning to install radiant barrier
- 24" joist spacing (2" x 4").
- the board in the pics is a 2 x 4 perpendicular to two joists.
- following some calculator online I got 8 sqft needed for total inlet ventilation .
- 20 joist gaps on each side of the house = 40 total.
- 8 x 144 / 40 = 29 sqin ventilation per joist gap

A few of these exist:

...but most are like this:

This is a rough idea of what I would need if cutting one hole:

I would need 8 holes like this at 2"

...or 4 holes like this at 3"

Another option is yanking the 2 x 4 out (cutting the nails) and installing this 3 x 22 vent:

...or this one

I guess I am mainly asking if this is a structural issue. Any advice???
Old 03-09-14, 04:27 PM
Join Date: Oct 2008
Location: New England
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Not a structural issue I don't believe. But those openings will have a lower NFA (net free area) when covered with a bug screen.

But you are dealing with a catch 22. The cooler the attic gets the less ventilation you will have. naturally vented attics can essentially, at best, reach half way between their normal peak and outside temperatures. They will never equal the outside unless you power vent and that is another discussion.

The approach often recommended when you have ducts and equipment in an attic is to foam the bottom of the roof, called a hot roof. This approach has its pluses and minuses.

If you don't go with the hot roof, step one is air sealing for the ducts, equipment, and between house and attic. Follow that with maximum insulation levels for the ceiling, ducts and equipment. Once everything is super insulated and air sealed, that attic can get hot with little effect on the home below.

If at some point you replace the shingles above, there are new materials that reflect much of the heat before it gets into the attic.


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