Sealing rim and attic joists in balloon frame homes


Old 07-24-16, 04:01 PM
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Location: USA
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Sealing rim and attic joists in balloon frame homes

I have not posted on this site for over a year but previously was discussing my balloon frame house and insulating the rim joists. I sealed my basement rim joists with rigid foam cut-outs. I can easily access my attic wall joists as well but why do people say its also good to seal these up? My thought is that during the summer this would trap more heat inside the empty walls instead of allowing it to escape upward through the attic ventilation? I have aluminum siding on the house and interior walls are plaster/lathe. Thanks for the replies.
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Old 07-24-16, 05:02 PM
Join Date: Oct 2008
Location: New England
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It is standard best practice to have all wall cavities enclosed on all 6 sides. Any air flow can result in moisture transfer which is not good. If those cavities are empty, they need some insulation of one form or another. Blocking the vertical path needs to also serve as a fire block, what ever is required in your area.

Old 07-24-16, 07:20 PM
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You generally want your exterior walls to be insulated all the way to the attic (to the ceiling of the top floor). Then the attic floor gets a heavy blanket of insulation to reduce heat loss. The rafters remain insulated and the attic space is what should be ventilated... not your walls. Insulating the rim but not the walls would be a pointless endeavor. The whole point of insulating is to reduce heat loss and heat gain... it works both ways in both seasons.

When remodeling balloon framed houses, solid blocking (fire blocking) needs to be installed at the floor and ceiling to prevent the spread of fires. Additional blocking is usually needed if this distance is greater than 10' but local codes prevail.

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