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Old 03-12-2012, 07:48 PM   #1
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Venting Knee Walls


I have a 1 1/2 story house. They builder,previous owner, or someone has insulated the knee wall space and the top of the attic, however they insulated the slant in the attic so the insulation is touching the roof. It is too difficult (not enough room to move around) for me to remove this insulation and install baffels and then re-insulate, so I think I am stuck with the insulation.

I have gable vents and soffit vents, but there is no air traveling from the knee wall space up to the gables because of the blockage from insulation. So, I was wondering what would be my best bet for ventilating the knee wall space?

I am installing a new metal roof over shingles in a few months, so I am able to install for roof vents, but they would have to be only 6 or 7 feet from the eve.

Thanks for the advice.

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Old 03-13-2012, 12:35 PM   #2
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Venting Knee Walls


What type of insulation did they use on the kneewalls that is blocking the vent spaces?

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Old 03-13-2012, 01:09 PM   #3
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Venting Knee Walls


Installing metal roofing directly over shingles is not suppost to be done. The roof will rust out on the backside.
Since we have no pictures it's hard to see why it would be hard to get to that knee wall area.
Installing vents that low on the roof will do no good. Heat rises.
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Old 03-13-2012, 04:16 PM   #4
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Venting Knee Walls


They used fibreglass batts and also have some blown in stuff on top of that.

I am going to strap the roof before adding the steel, so there will be a 1 inch gap between roof and the old shingles.

I had to cut a hole in the bottom of the wall (from inside) to get to the knee wall space. The knee wall space is only about 3 feet wide and 4 feet tall at the highest end. I do not have room to pull of old insulation and then add baffels and new insulation. The only way to do this would be to remove the roof and go in through the top (I think).

I was hoping I could just add some type of exhaust vent toward the top of the knee wall space. Something that would work and not allow water/snow into the space.
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Old 03-13-2012, 05:32 PM   #5
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Venting Knee Walls


You could gable end vent each attic, above and below the knee-wall. Or, cut plastic baffle in 1/2, slip one in above the f.g., add another- pop riveting the sides together, etc. - to make a continuous run. Add caulking at the baffle joints where they overlap to join. Housewrap the attic side of the knee-wall and air block the floor under it:http://oikos.com/esb/51/sideattics.html

http://www.affordablecomfort.org/ima...pstars_sec.pdf

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Old 03-14-2012, 09:07 AM   #6
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Venting Knee Walls


You can vent that space just as you mentioned and GBR suggested.
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Old 03-14-2012, 09:33 AM   #7
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Venting Knee Walls


Since you are doing work to the outside, I would consider cutting a slot in the decking at the top of the knee wall space, strapping the roof from eave to ridge, cutting a slot in the decking of your attic space, then installing a ridge vent. This way the air will travel through the soffits into the knee wall space, through the slot, between the new and old roof, and then into the attic and out the ridge. I would suggest removing the shingles. This is also an opportunity to add more insulation in the form of rigid boards.
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Old 03-14-2012, 09:48 AM   #8
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Venting Knee Walls


Quote:
Originally Posted by shazapple View Post
Since you are doing work to the outside, I would consider cutting a slot in the decking at the top of the knee wall space, strapping the roof from eave to ridge, cutting a slot in the decking of your attic space, then installing a ridge vent. This way the air will travel through the soffits into the knee wall space, through the slot, between the new and old roof, and then into the attic and out the ridge. I would suggest removing the shingles. This is also an opportunity to add more insulation in the form of rigid boards.
Great advice.

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Old 03-15-2012, 08:39 AM   #9
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Quote:
Originally Posted by shazapple View Post
Since you are doing work to the outside, I would consider cutting a slot in the decking at the top of the knee wall space, strapping the roof from eave to ridge, cutting a slot in the decking of your attic space, then installing a ridge vent. This way the air will travel through the soffits into the knee wall space, through the slot, between the new and old roof, and then into the attic and out the ridge. I would suggest removing the shingles. This is also an opportunity to add more insulation in the form of rigid boards.

This sounds like it will work. I have a couple questions: when strapping the roof, I would normally run the strapping horizontally all the way up the roof about every 24". Are you suggesting that I run the strapping vertically? If I do run it horizontally, will there be enough room for the air to flow between the old roof and the metal roof, with the strapping in the way?

Also, do you suggest a small slot between each rafter, or a larger slot between just a few rafters?

Thanks.
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Old 03-15-2012, 09:51 AM   #10
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Venting Knee Walls


Air seal the floor and get the kneewall connection to the conditioned space tight and your ventilation needs are very small.

At that point, I might go the gable end vent route as it will eliminate the punching holes in the roof deck.

The strapping will have to be run vertically or you will have to run double strapping to create the vent space.

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