So I’m building a house right now, and am thisclose to inspection before insulation/drywall. I’m installing Accuvent rafter chutes yesterday afternoon with my FIL looking on. I’m fixing to install them in every bay (about 50 total).
Sez he, “You don’t need to put ’em in every single bay, you know – that’s not what they do. They just put them over the places where there are vents, then stuff batts in the spaces where there aren’t.”
Sez I, “I don’t really GARA what ‘they’ do. ‘They’ aren’t responsible for my house.” But…there is some logic to what he said – what’s the point of putting ventilation chutes over places where there aren’t soffit vents? OTOH, I want to make sure as much air gets into my attic as is necessary.
We’ve got what I think is a pretty standard soffit – aluminum panels, with every third being a ventilated panel. Continuous ridge vent.
So… what’s best practice here?
Jason
Replies
Do 'em all. You should have more soffit vent area than one chute will flow.
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Why aren't you using continuous soffit vents?
You need 1 sq ft of venting for every 150 feet of living space.
That venting needs to have the same airflow at soffit leading in as it does at ridge leading out or it is ineffective. The airflow will be limited by the smaller allowance of the too.
And yes, you should have flow baffles in EVERY rafter bay. Even without enough venting, the spoace will go a long way to maintaining a cold roof, which is the goal.
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I believe every bay is best.
In my area, the square footage ratios don't bear much relation to reality: 150:1 without a ceiling VB, 300:1 with a VB.
My understanding is those figures were simply "made up" decades ago.
Even air flow acoss the entire underside of the sheathing is what seems to work best.
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If you don't have continuous vents then you only need the chutes in the bays with vents. With continuous vents you could do every bay, but generally every other should suffice.