# Attic Insulation - Baffles, Air Flow Questions



## jklingel (Dec 21, 2008)

Good move to insulate w/ cellulose. You absolutely need ventilation, about 1 sqr ft per 150' sf of roof (some folks say up to 300 sf). More vents on the bottom than top is best. Greenbuildingadvisor.com just had a blog (or reference to it in another one) about this. Keep insul away from any boxes, fan, vents, yes; at least 2" of air over insul where it meets the edges of the roof. Lights that are covered should be approved for such, not just any light; check w/ local elect company or building dept.


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## joecaption (Nov 30, 2011)

If it was my house I'd get rid of the gable vent and powered vent and add a ridge vent. 
Then the whole roof gets vented not just the ends or a circle where the vent is.


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## majch (Mar 22, 2012)

Do i need to place sheet metal around the electrical box to protect it?


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## jklingel (Dec 21, 2008)

Joe: That is a good point. The power vent may cause a negative pressure in your attic, which tends to draw air from the conditioned space into the attic. That is not good, as that losses heat and brings moisture w/ it. That was mentioned the the gba blog I mentioned, and why more vent on the sides is better than the top, if you have any on top. It still seems, intuitively, that the negative pressure would be tough to get, with lots of soffit vents, but that is what apparently happens. Check locally for what is required over lights. There may be particular specs for material and distance from light, as well as wattage, etc.


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## Gary in WA (Mar 11, 2009)

If the gap next to the rafter blocking has a screened vent, or continuous screened vent, the baffles need to protect that gap from insulation. Your baffles are good for the roof sheathing to direct soffit (intake) air up, but are lacking the (lower) wall insulation-blocking part: http://www.bergerbuildingproducts.com/productsAccuvent.html
See how those block the incoming air from the insulation directly over the wall? You could add the "Windblocker" from Lowe's to compensate...
More heat is lost at the exterior wall because of minimal insulation (low height restriction) and incoming soffit air wind-washing your hard-earned work/money.

Recessed can lights only need to have a box, and only non-rated; IC = insulation contact.

Per Electrical Code, you need to protect any wires within 6' of the downstairs access, so a future H.O. won't step on the wires on the ceiling joists.

If you decide to leave any attic flooring in place and blow cellulose over it, check on it periodically for mold under the sheeting because the drying air flow will be blocked by the new cellulose. Elevated cat-walks are nice. May need to build an insulation box for the drop-down stairs and store the window screens elsewhere. If you haven't had attic moisture problems- mold, rusty nail ends, etc., I would leave the ventilation system, as-is. Powered exhaust fans do pull air from the closest source, your gables, which will help move the stagnate air, and draw moisture from the convective loops at each side of the ridge.

Gary


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## majch (Mar 22, 2012)

Thanks for all the replies. It’s clear I have an issue in that the baffles I installed have left a gap and are lacking the (lower) wall insulation-blocking part. I should’ve installed the part that GBR recommended. Tearing down 40 and re-installing them isn’t the best option for me mentally, so:

I think I have 2 options:

1.) Install an ado product that will block the air









2.) Put batt fiberglass insulation to fill the gap so that my blown insulation doesn’t cover the soffit

#2 would be easier for me, but my understanding is that air would still get in. I have searched high and low (amazon, HD, Lowe, internet) and no one has any ADO product in stock. Anyone have any feedback on what I should do?


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## Gary in WA (Mar 11, 2009)

Install rigid foam board, foil-faced, on end, over the wall. Each one cut longer to fill-in solid when side-by-side. They would need to be can foamed at the top as each baffle is variable in the rafter/joist space. Or, just put some f.g. batt in a plastic bag and shove, though the area directly over the plate would not meet minimum R-value and lose R from compressing. Either way- over the exterior wall is the most heat loss (ice dams) and that area is the most wind-washed: http://books.google.com/books?id=3kLLZBKa5zAC&pg=PA70&lpg=PA70&dq=Silerbsein+1991&source=bl&ots=1JP4IBaEbX&sig=Bh8KD6UW2SZ74R0QxwqeCjlOVLY&hl=en&ei=6Y8NTdb0FpH4sAPp4LDnAQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CB8Q6AEwAg#v=onepage&q=Silerbsein%201991&f=false


http://www.arc.thermaldr.com/res_pg_3.htm

Gary


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