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Old 02-27-2010, 04:30 AM   #1
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Insulating Rim Joist... Alternative to DOW Thermax?


We have a bi-level... lower floor is ground level; no stairs going down. Stairs go up to the main living area. Despite nothing being below-ground, our lower (ground) level is significantly colder than upstairs.

We are replacing the panels in our drop ceiling down there, so access to the rim joists is easy; we can easily see the rim where the upper half of the house was mounted on the ground half (shown in this thread).

We want to insulate the rim joists -- as shown here or here-- but have read other places, including on the rigid insulation itself, that it needs a thermal barrier. Do we need to cut identical-sized squares of drywall and somehow mount these on top of the foam in the rim joists?

The other option was to hunt down some DOW Thermax, but unfortunately the nearest distributor to us is 2 1/2 hours away, and a 4'x8' sheet costs almost $80. That's a lot for one specialized insulation for the rim joists. Is there any alternative to this? Do we need to suck it up and go get the Thermax, install drywall over the foam in the rim joists, or do we not need anything at all but the foam, if it's up in the rim joists above the drop ceiling?

Thanks!

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Old 02-27-2010, 04:16 PM   #2
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Insulating Rim Joist... Alternative to DOW Thermax?


bump!

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Old 02-27-2010, 04:26 PM   #3
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Insulating Rim Joist... Alternative to DOW Thermax?


I had an area (unfinished knee wall area) where there was just some pink fluff stuffed into the rim area between joists. I took out the fluff and rough cut some 2" XPS (pink) to fit the area and aplied some expanding foam around the joints between the joists, floor and the rimd and then jammed in the cut XPS. I then cut new fluff to fit loosely. Then, I covered the area with with 2" XPS that was glued to the block walls. It made a world of difference in the storage area under and entry to a split home., but it probably did not not do much more economically than just foaming to cut the infiltration typical with the wood portion of a house.

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Old 02-28-2010, 05:14 PM   #4
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Insulating Rim Joist... Alternative to DOW Thermax?


Is there any sort of safety thing as far as leaving the rigid pink foam exposed (up in the joists above the Armstrong drop ceiling in our lower level)?

I've heard some mixed things about needing to cover it with drywall.... toxic fumes, combustible, etc.

The DOW Thermax said it had a thermal covering so it didn't need to be covered by drywall like regular rigid foam. I just didn't know if this was really necessary, or if I could just stick the XPS in there, foam it, and leave it uncovered.
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Old 03-02-2010, 02:31 AM   #5
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Insulating Rim Joist... Alternative to DOW Thermax?


Anyone?
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Old 03-06-2010, 02:36 PM   #6
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Insulating Rim Joist... Alternative to DOW Thermax?


I'll take that as a no...

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