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Old 01-23-2010, 06:08 PM   #1
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Plastic air vents

I have a 50's era cape cod house that has a soffit in the back of the roof, and a Cobra ridge vent. My roof in the back is raised up (cathedral ceiling). I believe my soffit is cloged with insulation bats right now. I plan staple the plastic airvents on the back roof joists. My question is: Should I put airvents in every joist bay in the back of my roof? And should I run the airvents all the way up to the ridge vent?


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Old 01-23-2010, 06:21 PM   #2
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Place them between every truss that has a intake vent.
Run them from the eave to the open space/ crawl space, even in those tpye of ceilings the ceiling will stop a foot or so below the ridge of the roof structure.


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Old 01-23-2010, 11:16 PM   #3
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With soffit in back and cathedral rafters, install an air baffle in each rafter bay. Also install the Windblocker piece to protect your fiberglass batts from wind-washing over the wall: Or, you could buy the other type that bends and staples over the end of the batt to the wall, then runs up the rafter: Remember to leave 1” between baffles, as per instructions.

In a Cape, be sure to block the air with foam board above and below the knee wall, to keep the cold outside air from your insulation. Use foam board on the attic side of knee wall if insulating the floor there:

Un-clog the soffits and make sure the soffit vent NFVA equal the ridge NFVA, for a balanced system. You may have to add soffit vents:

Especially if the existing vents are 4x16 and 8’ apart, much too little venting. If the ridge is rated at 18 in. per ft., you need 9” per ft. on each side of roof at soffits. You’ll be surprised after you do the math: 1/150 unless with an attic poly:

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Old 01-24-2010, 03:56 PM   #4
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knee wall

I have two dormers in front of my house facing south. In my knee walls I have two book cases in each room inside the wall. In the center of the building were my closet is I can access my other knee wall by a crawl space. This knee wall crawl space has drywall on the roof joists. I verified there was insulation in the joists of my front roof in the attic by pulling some insulation, and feeling with my hand in the knee walls. My question is: Should I put the pink isulation board between gap in the knee wall in the attic? Does it matter on the size of the board? Because I have some 2" board left over. Can I use that one? Also when you mention about blocking the knee wall bellow. How should I do that?
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