Insulating 2nd floor wall over cantilvered floor


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Old 09-10-18, 05:33 PM
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Insulating 2nd floor wall over cantilvered floor

I live in Maryland. The 1st floor of my house sits on a concrete slab foundation. The walls are filled with fiberglass roll insulation. The whole house was then wrapped in brown cork board sheathing, overlaid with another layer of large thin foam sheets, which I think are taped, and then vinyl siding or brick.

On the front of my house, the 1st floor wall is brick, the 2nd floor is vinyl, and the 2nd floor overhangs the 1st floor by about a foot. Based on my memory of a prior repair, I think they didn't properly insulate the overhang section of the 2nd floor. I think they just stuck some fiberglass insulation in the cantilever area without any blocking or sealing.

I have just read several articles about how the cantilever should have been insulated
but I am wondering if properly insulating the cantilever insulation will actually fix the problem we have. The problem is that in the winter, the 2nd floor wall always seems extra cold.

1) Do you think correcting the cantilever insulation will fix the cold wall?

2) To add blocking, it seems like foam board will be much easier than wood?

3) For those who have removed plywood covers from a cantilevered floor above a brick wall, it is usually fairly easy to remove and reinstall the plywood?

I am hoping that I will just be able to remove the nails, and then use a putty knife to break the seal between the plywood and the mortar and the top of the brick wall. To me, the worst case would be disturbing the mortar or if the plywood is held in by nails that are blocked by the brick.

Thank you in advance for your advice.
 
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Old 09-10-18, 06:24 PM
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Hard to say without seeing it. But the 2nd floor cantilever will be covered with plywood "soffit" and it's possible that it extends behind the face of the brick 4" or so... removing it may be very difficult (if not impossible, because you can't remove the nails above the brick) and yes, you might damage the mortar and brick in the process. Its hard to advise you what would be best sight unseen.

Often the best thing to do it to pull carpet back and tackle this problem from the inside by cutting out the subfloor. Air does often channel down the floor joist from a poorly insulated rim joist and cantilever. Having the area professionally spray foamed would likely be the best solution as it would guarantee an air tight perimeter.

If the wall is cold I would suspect poor insulation... although the heat loss in the cantilever would be partially responsible for some of the cold on that wall.
 
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Old 09-11-18, 06:20 PM
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Thank you.

I previously added an outlet in the 2nd floor wall. The stud bay was filled with fiberglass insulation.

I now realize that there's no way to get the plywood to slide out from the brick area.

Instead of doing the job from the inside by moving furniture and carpet and cutting the subfloor, do you think the plan below might be a bit better or at least equal? I'm afraid it will be harder to reach to reach under the soffit from above, but if you still think cutting the floor is best, please let me know.

New plan:
Cut plywood in front of the brick wall, remove plywood and do the insulation work, then reinstall plywood, plus a new piece of trim that matches the existing trim to hide the cut seam.

I've attached some pictures of the soffit from left to right,
 
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Old 09-11-18, 06:24 PM
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That would probably work.

Fiberglass doesn't stop air, it only slows it. So if the wall is insulated but still cold, it's likely that you have a lot of air moving through the insulation for some reason.
 
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Old 09-14-18, 10:23 AM
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I have 2 more questions about blocking the air movement in the wall.

1) How should the bottom of the wall be sealed to prevent air entering the bottom of the wall behind the foam wrap. Currently I don't think there's anything to block air from entering behind the wrap. I think it just hangs down past the cantilever soffit and stops.

2) From the attic, I have sealed the top plates of most of the interior walls, and the side exterior walls that are more accessible where the attic ceiling is taller, but it's very hard to get access to seal the top of the exterior walls in the shallowest part of the attic. (Attic has loose fill insulation). Are there any pro tips to making that job easier? I was just using a can of great stuff spray foam.
 
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Old 09-14-18, 10:52 AM
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If your house has Tyvek, it should extend over the soffit and all the edges should be taped if you expect it to act as an air barrier. Almost no one does that. Mainly because you can't tape very well to a dirty old house. The best way to air seal older homes is to open up the walls, remove all the plaster and lathe and have the walls professionally spray foamed.
 
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Old 09-14-18, 03:45 PM
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My house was built around 1980. No plaster or lathe. Walls are studs and sheetrock, with fiberglass insulation in all the stud bays. It doesn't have tyvek. It has sheets of some kind of gray foam about 1/4 thick, and I think it's taped at all the sheet seams.

Sealing the top plates from the attic was very effective in the locations I could reach, but its hard to reach the exterior walls from the shortest part of the attic.
 
 

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