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floor insulation & converting garage


rickls's Avatar
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Join Date: Mar 2013
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NY

03-03-13, 07:58 AM   #1  
floor insulation & converting garage

I am going to convert my 2 car garage into a family room. I will be raising the floor installing floor joists etc. My question is what would be best way of insulating the cold concrete floor.A lot of what i've read says the closed cell spray insulation as this is also good for moisture & also acts as a vapor barrier.
should i also use plastic sheeting on floor first? i am also going to be running some duct work in the floor joists so i cant really use fiberglass batts in joists.
any thoughts or web sites for info appreciated.

 
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Nashkat1's Avatar
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03-03-13, 10:24 AM   #2  
You need plastic sheeting on the slab iff you have a moisture problem there. That said, you need to test for moisture from the slab by laying out a couple of pieces of plastic during wet weather and seeing what collects under them.

PT lumber for the joists, and polyiso or mineral wool between them should work. Others should be along with more advice.

 
chip wolff's Avatar
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03-08-13, 04:17 PM   #3  
Will there be a space between the new framing system and the existing garage floor? How much?

 
rickls's Avatar
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03-16-13, 05:43 AM   #4  
yes,was going to set joists on 2x treated laying flat. so 1-1/2"
yes

 
Nashkat1's Avatar
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03-16-13, 07:38 AM   #5  
The pressure treated sill plate is part of the framing system. If the studs (not joists) are standing on that, then there will not be a space between the new framing system and the existing floor.

I'm not sure why Chip wanted to know that...

 
Gary in WA's Avatar
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03-16-13, 12:17 PM   #6  
I'd set the joists on p.t. sleepers (w. 1/2" XPS under- for a thermal break) and fill between with 2" XPS (R-10), then add cavity insulation per code. Either R-19 or R-30 (see footnote "g") as you may live in Zone 4,5, or 6, lol; check cities below map;Chapter 11 - Energy Efficiency

I'd caulk all joints air-tight to the slab, similar to this in fig. 7; BSI-009: New Light In Crawlspaces — Building Science Information


Ideally, the foamboard would go under the sleepers, depends on the local AHJ and your own state building code. The energy site I gave above is from 2009 IECC (one from which your state energy code is based on) 2010 NYSECC. Chapter 4 - Residential Energy Efficiency
The problem MAY be the foamboard's compressive strength though most are rated at 15 or 20# per sq.inch or 2x4x24" long bearing would be 1260# per piece w. 15# f.b. That would hold up one end of a joist.... even with a car, lol. Run the joists across the garage instead of with and just punch another hole at house side wall for ducting there. You can leave a gap above the insulation as per link to BSC, may help with duct clearance.

Gary

 
rickls's Avatar
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03-20-13, 02:38 AM   #7  
thank you to all for info. have some more reading and thinkin to do (lol)

 
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