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Old 09-20-2014, 11:16 PM   #1
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Insulating Cantilever Containing Water Pipes


Looking for suggestions on how to insulate a cantilever space containing hot/cold supply pipes and a bathroom exhaust vent. Above the cantilever is a bathroom, below is the entrance to my house and on the inside another bathroom. Currently there is only fiberglass, no blocking, no foam, no sealants. The pipes have been there since 1984 and since I live in a middle unit townhouse they will not be moved.

Should I install rigid foam just below the living area sub floor as well as just above the exterior sheathing/ceiling? Also, should I build a rigid foam box around the pipes but then leave the box open to the conditioned air from the house?
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Old 09-20-2014, 11:32 PM   #2
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What is wrong with the insulation that is there now?
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Old 09-20-2014, 11:43 PM   #3
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Good question. I am going to replace the ceiling/sheathing. It was sagging three years ago when I bought the home and repaired by the past homeowner at the same time per home inspector recommendations. It is now sagging again so I want to pull it off to see the condition and properly fasten new and thicker plywood. Also, I first got a view of the insulation recently as I am remodeling the bathroom on the level below the cantilever. I saw what appeared to be some type of mildew on the insulation directly below the hot water pipe as seen in the first picture . Figured it would be best to replace the insulation and throw some pipe insulation on the water lines as well.
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Old 09-21-2014, 07:39 AM   #4
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Do not put insulation at the subfloor level. That would lessen the heat sink to that space and those pipes would freeze in a New York second.

Rigid foam or spray foam (spray foam will be much easier for the outside edges) are your friend.

Move the insulation to the outside wall edge and bottom (i.e. the areas that adjoin the outside air).

Seal all the gaps and cracks and don't under apply.

That will keep that space warm and above freezing.
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Old 09-21-2014, 10:09 AM   #5
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The moisture is coming from the exhaust fan, even though the space is insulated it doesn't look to be conditioned. Often a heat duct is run into cantilevered sections to introduce some heat.

I would make sure that the area is sealed (air sealing) and then insulate with properly installed batt insulation. You could get a DIY spray foam kit, but if you are not experienced with spray foam you should attempt it in such a critical area. You can use spray foam to air seal and then rigid foam insulation. You can even seal the rigid with spray foam.

Those are the two methods I would recommend.

Remember air sealing is just as important as insulation.
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Old 09-21-2014, 10:32 AM   #6
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Quote:
Originally Posted by zackz5 View Post
Good question. I am going to replace the ceiling/sheathing. It was sagging three years ago when I bought the home and repaired by the past homeowner at the same time per home inspector recommendations. It is now sagging again so I want to pull it off to see the condition and properly fasten new and thicker plywood. Also, I first got a view of the insulation recently as I am remodeling the bathroom on the level below the cantilever. I saw what appeared to be some type of mildew on the insulation directly below the hot water pipe as seen in the first picture . Figured it would be best to replace the insulation and throw some pipe insulation on the water lines as well.
I missed the part about the ceiling replacement.

That will provide you the perfect time to insulated it properly.

Best of both worlds would be apply rigid foam to the underside of the framing prior to re-installing the new plywood.

If you don't mind the slightly lower ceiling height (i.e. by whatever the foam depth is) that is the best route to go.

Seal all the gaps an cracks once you have it open and you can also install the rigid foam at the outside wall inside of that space.

No need to buy a spray foam kit if you have that kind of access. Caulking and canned foam will work fine.
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