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Old 07-11-2019, 07:40 PM   #1
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Knee wall to conditioned space


Hey all. I have some knee wall attic spaces that have hot water pipes running through them. They currently are just storage spaces with fiberglass batt insulation on the attic side of the drywall. I would like to make them semi conditioned spaces so the pipes are protected. What would be the best method to go about doing this? I was considering screwing rigid foam board directly to the rafters, foaming all joints and leaving the batt insulation where it is. Thoughts?
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Old 07-11-2019, 07:49 PM   #2
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Re: Knee wall to conditioned space


Are the pipes down in the joists or on top of them..
You have to consider air leakage from the house, venting high and low before you add insulation.
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Old 07-11-2019, 09:27 PM   #3
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The pipes are above the joists. Basically run right in the corner between the joists and studs for the interior walls.
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Old 07-12-2019, 12:11 AM   #4
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Re: Knee wall to conditioned space


Hi Kyle, where are you??
Your climate is part of the "how to" you need.

If you have some cold weather then "semi conditioned" can be a problem with warm air from the house getting into a cooler space without ventilation. So you need to make that warm conditioned space with a good air barrier towards the outside and plenty of insulation.

I'll wait for the where answer.

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Old 07-12-2019, 06:14 AM   #5
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Hey Bud,
Thanks for the reply. I am in NJ, so I do have to contend with cold weather.
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Old 07-12-2019, 09:53 AM   #6
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Re: Knee wall to conditioned space


Here's an article that illustrates two ways to insulate the devils triangle.

One of the problems you will face is the inbetween nature of closets and attic spaces as you have. The divide between that space and the heated home makes those spaces cooler and i've seen many closets develop mold due to a lack of conditioned air.

Been awhile since I read that link so I'll let you read and answer questions in needed.

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Old 07-12-2019, 07:22 PM   #7
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Bud,
Great article, thank you for that. My thought is to put styrofoam baffles against the sheathing in the rafter bays, put unfaced fiberglass batts in between the rafters, and screw Dow thermax or XPS to the rafters as the air and vapor barrier (taping/caulking/foaming all joints). What do you think of that plan?
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Old 07-13-2019, 05:33 AM   #8
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Re: Knee wall to conditioned space


Quote:
Originally Posted by Kyle3427 View Post
Bud,
Great article, thank you for that. My thought is to put styrofoam baffles against the sheathing in the rafter bays, put unfaced fiberglass batts in between the rafters, and screw Dow thermax or XPS to the rafters as the air and vapor barrier (taping/caulking/foaming all joints). What do you think of that plan?
Did you notice that in both pictures there is venting between roof deck and insulation and the one with a nee wall has blocking under the floor to separate warm space from the attic .
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Old 07-13-2019, 09:04 AM   #9
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Re: Knee wall to conditioned space


Thermax would be a great choice, high r-value and it can be installed without concern for an additional layer of drywall. Remember to do the end walls as well.

Once you insulate and isolate those side attics you need to share the inside conditioning to keep the inside surface of the new insulation layer above the dew point. Depending upon your access to this space some will install a louvered or vented door.

Bud
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Old 07-13-2019, 10:06 AM   #10
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Neal, yes I noticed that. That is why I plan on installing styrofoam baffles on the underside of the sheathing in the rafter bays. Thermax cut to size to go between floor joists.

Bud, does the unfaced fiberglass seem like a good plan in addition to the thermax? My thought with going with the unfaced batts is only one vapor barrier (the thermax board), while still adding r value. Each knee wall has a hollow access door. I can certainly add some type of vent to keep it the same temp/humidity as the rest of the space. The doors are leaky to start with, so it shouldn’t be too much of a challenge.
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