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Old 06-03-2008, 10:13 PM   #1
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Attic with no ventilation

I am renovating a house that has an addition that seems to be built incorrectly. The house was originally u-shaped, but is now square. The part that they filled in has roof joists spanning the gap (about 12 feet) instead of running up and down (does that make sense?)

Being in northern Canada, it has about 8 inches of insulation, and due to the low slope, the joists don't allow for any attic ventilation (see attachment for poor drawing) and there has been some water stains and water damage. There isn't even soffit on the outside.

My first thought is to open it from the outside and install soffit, but my question is, can I drill a series of holes in the joists to allow airflow through the lower, clogging joists? I have found sites that say you can drill up to 3" on 2x10s, but how many can you put in?

The moisture isn't terrible, so I'm hoping even a few holes would fix it. The rest of the house vents fine, and the addition is open at the upper end of the attic.
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Old 06-04-2008, 08:25 AM   #2
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You must cross-ventilate the attic in order to achieve effective ventilation. Air must flow through it.

Your idea of drilling the rafters isn't a bad one at all. They make very small circular shaped louvered/screened vents for venting things such as columns. They're in the neighborhood of 2" or 3" diameter.

According to the International Residential Code, you can drill your rafters as long as you stick to the following:
-min 2" from bottom
-min 2" from top
-round hole
-hole must be no larger than 1/3 of the depth of the member (9-1/2" member...max 3-1/8" hole for example)

I'd drill some vents into the soffit you drew (or outer rafter if the soffit isn't an option) to open it up to the outside a little. Then put some in the interior side to allow airflow into the rest of the attic.
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Old 06-04-2008, 11:20 AM   #3
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Would one of these products help for you?

There is a roof forum you can bring this question up.
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Old 06-04-2008, 06:07 PM   #4
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Drill you 2" - 3" wholes on the outside first as Thekctermite has stated. then get your self an electrician's wood drill bite at 1" with a 18" extension. Drill through the vent whole you just drilled on the outside in through the other rafters, when finished plug the outside wholes with the vent plugs.

Last edited by buletbob; 06-04-2008 at 07:10 PM.
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