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Insulate upper story cantilevered over kitchen bump out

Insulate upper story cantilevered over kitchen bump out

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Old 02-20-21, 07:25 PM
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Insulate upper story cantilevered over kitchen bump out

Evening!
A bathroom leak resulted in partial drywall removal in kitchen. Outer walls are where ac / heat are run, inner walls are returns.

Over the kitchen there's is a 3 foot ish cantilevered upper story. When drywall was removed outside chilled air was literally pouring in. No vapor barrier was seen, but since the kitchen also has plumbing above in the boxed out space above the cabinet I'm assuming I wouldn't find one.

I've been slowly wrecking more drywall trying to seal air leak . If you're aware if the date you know a massive cold spell had hit everywhere.

After my 10th joist stuffed with pink insulation, is there a better way? Can I get a foam gun extension or pipe, drill a small home either inside or outside, and shotgun a can in there?

Ideas welcome. I can keep destroying drywall... It'll make the regret profound for ever having bought this place.
 
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Old 02-20-21, 07:44 PM
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If you have a 3 ft cantilever, it needs to be attacked from the outside by removing the soffit under the cantilever. Fiberglass usually leaves a gap either above or below the insulation, (or both) creating a path for air to blow across the insulation and down the joists.

Plumbing needs to be kept on the warm side of the insulation, and often in climates where it rarely freezes, that fact escapes most ppl. That's largely why there are such problems during these arctic episodes.

To block air coming down the joists you need to air seal both the rim and the bottom of the cantilever. Best way is with commercial spray foam... 2nd best is with 2" of rigid foam, and air seal all edges with PL300 or some other latex caulk or spray foam... then stuff insulation against that from inside. And typically you put solid wood blocking the joists where the cantilever rests on top of the exterior wall. The interior of that blocking can be insulated with foam as well but its not as critical at that point if you did everything else right.
 
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Old 02-21-21, 05:34 AM
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Thank you. There are no soffits (holes), just that really cheap particle/melamine board that is failing. Siding is (probably) asbestos cement shingles.

Those joists (and the gap) come right into the house, unabated, and enter the walls/ceilings. I'm really floored looking at it- they left it out there, stuck some pipe in places for bathrooms, and stuffed a 1' wide piece of fiberglass in there and called it a day.

Just to be sure I'm hearing what (I feared I would hear), removing the bottom soffit material, spray-foaming all attachment points for joist/wall; any gap, and then stuffing with insulation for the mice that inadvertently get in to it and scamper along the walls...

I'm boned, aren't I? This ain't happening in this arctic period for sure. Probably best to close up the wall for now and hit it in the summer instead.

I tried running a scope cam down the bump out portion but couldn't make much out. Too much insulation in some places to push away/aside.
 
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Old 02-21-21, 07:41 AM
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The spray foam i'm talking about is a commercial product that is sprayed with a big gun. The canned foam you buy at the store is not going to help you because you have too big of an area, and you can't spray can foam in a way that coats everything. It's very expensive to have done. Which is why 2nd best is cutting up 4x8 sheets of 2" thick rigid foam, fitting those pieces between joists, and make a barrier on the outer rim and lowest parts of your cantilever framing with that. THOSE edges could be sealed with either caulk or great stuff foam in a can.

Soffit refers to the material nailed over the bottom of your cantilevered joists... usually should have been made of AC plywood. yes, it has to come off in order to do this. You will likely end up putting new soffit on when you put it back together. If you have plumbing in there, then yes, you likely should wait until spring to open it up.

Your best move temporarily is to insulate under and behind any pipes (on the exterior side of those pipes) and leave the pipes completely exposed on the inside so that they can be warmed by your interior air. That will usually keep them from freezing. You can also point a fan at them on the inside to ensure they get warm air.
 
 

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