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Old 10-25-2010, 04:00 PM   #1
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using foamboard....moisture barrier needed?


I plan on using foam board for insulation in my basement walls during a remodel since they resist moisture better, however, never used it before (only used batts). Do I need to install a moisture barrier between the sheetrock and foam board (ie: 4 mil poly)? Also wondering if I need to leave a gap between the foamboard and sheetrock to allow a little air movement? (ie: only use 1/2 inch thick foamboard even though there is room for 3/4 inch thick?)

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Old 10-25-2010, 05:59 PM   #2
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using foamboard....moisture barrier needed?


Foam board is usually Expanded Polystyrene, which is only for drink cups and meat trays at Walmart.

The better materials are Extruded Polystyrene, that is stronger, heavier and has more insulating properties.

Dick

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Old 10-25-2010, 09:04 PM   #3
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using foamboard....moisture barrier needed?


FYI concretemasonry.......that's really what I meant to say I was going to use. I call that crap styrofoam. I'm not a big construction guru, so my technical terms aren't always proper. Any thoughts on my previous question of whether I need to use a seperate moisture barrier? I know extruded polystyrene is very moisture resistant, but wasn't sure if i needed a seperate moisture barrier.
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Old 10-25-2010, 11:13 PM   #4
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using foamboard....moisture barrier needed?


Dick is probably out catching another "catch and release"..... lol.

Where are you located?

http://www.buildingscience.com/docum...gs?full_view=1
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Old 10-25-2010, 11:44 PM   #5
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using foamboard....moisture barrier needed?


located in North Dakota. thanks for the article, although some of it certainly goes over my head. i read a section in there that says you shouldn't use more than 1" of extruded polystyrene for insulation? I was going to use 2 inch for the bottom half of my wall (where I will be building a ledge, thus, have more room for more insulation). Apparently that's not a good idea?
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Old 10-26-2010, 12:13 AM   #6
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using foamboard....moisture barrier needed?


Parts of that article have been updated, others, not. 2” is now suggested below grade, none above grade, interferes with summertime movements. Cold climate, the 2" keeps the inside of foam board warm enough not to reach the dew point and condense. No vapor barrier. Foam b. covers the top of concrete stem wall, air seal foam/caulk at bottom edge of existing sill plate/concrete. Latex paint inside, unfaced insulation. No air gap between f.b.and batt for convective loops: http://oikos.com/library/insulating_...lls/index.html

http://www.buildingscience.com/docum...ent-insulation

Fire-stopping every 10' horizontally required per code. And at top of walls into floor joist bays. Use the foam board to air seal the rim joists--- very important: http://www.rd.com/57548/article57548.html

Sill sealer under the p.t. bottom plate for a thermal and capillary break (pt is not waterproof): http://www.greenbuildingadvisor.com/...-building-code

Gary

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