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  1. #1
    Join Date
    Aug 2008
    Location
    Hamilton, ON
    Posts
    7

    Default Attic kneewall insulation - proper roof venting?

    Similar to another user, we are looking to insulate our attic kneewalls. We have a 2 1/2 story double brick home; the pitched section of the attic is insulated with interior vapor barrier but the kneewall sections are uninsulated. We're looking to use blown cellulose to the floor area and then either fibreglass bats or polyurethane to the backs of the kneewalls. The insulation contractor we spoke to told us we need to make sure the cold attic spaces are properly ventilated. Between him and a roofing company I spoke to, I understand we should have soffit venting coupled with roof vents. We have a few roof vents and could install a few more. Any air from the kneewall spaces will have to pass through the fibreglass bats that currently insulate the pitched sections as we can't assume they left a decent gap on the cold side for air to pass through. The problem seems to be soffit venting. The house has gorgeous wood dentil detailing on both the soffit and fascia that would be destroyed by installing soffit venting. The detailing is absent along the back of the house, so we could do soffit venting there, but it runs the entire length of the front of the house, as does the front kneewall. What we'd like to understand is how crucial adding the soffit venting really is? Are we going to rot out our roof if we don't install the venting? How is this handled in other old homes? We're trying to do the best we can but also keep historical character, but we need some help here. We need to use that attic space and it is COLD in the winter and HOT in the summer (despite having AC up there), plus our winter heating bill is outrageous!

    Thanks so much!

    Caroline

  2. #2
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Attic kneewall insulation - proper roof venting?

    Quote Originally Posted by wheatandhoney View Post
    Similar to another user, we are looking to insulate our attic kneewalls. We have a 2 1/2 story double brick home; the pitched section of the attic is insulated with interior vapor barrier but the kneewall sections are uninsulated. We're looking to use blown cellulose to the floor area and then either fibreglass bats or polyurethane to the backs of the kneewalls.
    The insulation contractor we spoke to told us we need to make sure the cold attic spaces are properly ventilated. Between him and a roofing company I spoke to, I understand we should have soffit venting coupled with roof vents. We have a few roof vents and could install a few more. Any air from the kneewall spaces will have to pass through the fibreglass bats that currently insulate the pitched sections as we can't assume they left a decent gap on the cold side for air to pass through. The problem seems to be soffit venting. The house has gorgeous wood dentil detailing on both the soffit and fascia that would be destroyed by installing soffit venting. The detailing is absent along the back of the house, so we could do soffit venting there, but it runs the entire length of the front of the house, as does the front kneewall. What we'd like to understand is how crucial adding the soffit venting really is? Are we going to rot out our roof if we don't install the venting? How is this handled in other old homes? We're trying to do the best we can but also keep historical character, but we need some help here. We need to use that attic space and it is COLD in the winter and HOT in the summer (despite having AC up there), plus our winter heating bill is outrageous!

    Thanks so much!

    Caroline
    These types of conditions are tricky.
    First thing --- you are probably correct regarding any air space along the sloped portion of the roof/ceiling. In which case a ridge vent is somewhat useless trying to incorporate into using to vent the attic spaces on either side of the kneewalls.

    In most cases homes that have the configuration such as yours have 3 zones that are treated seperately --- 1 zone on one kneewall --- 1 zone above the flat part of the ceiling --- 1 zone on the other kneewall side.

    The zones of the attic side of the kneewalls can have vent grates installed on the gable ends ( one on each end ) at the lowest point of the attic space. Roof top vents located at the point where the top of the knee wall meets the roof .

    The top most attic space ( above the flat portion of the ceiling ) can have simple gable vents.

    Or ---- if you spend a liitle more $$ and want to use the space on the outside part of the knee walls ---
    turn those spaces into a semi-conditioned space by insulating the underside of the roof , the gable end walls , the floor , backside of the knee wall.

    Spray foam is ideal for this situation --- if it's in the budget.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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