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Old 01-16-2010, 11:16 PM   #1
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attic insulation-vapor retarder?


there is currently no insulation in my attic. i want to use this recylced paper stuff that is blown in. do i need to put a vapor retarder down first? i live in cleveland, ohio. i was thinking of laying on layer of r-15 faced for walls down first then blowing the stuff on top. but two rooms have been lowered from 9' to 8, so there is criss crossed studs that would make it difficult to lay the rolled insulation. is the vapor retarder necessary?

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Old 01-17-2010, 09:26 PM   #2
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attic insulation-vapor retarder?


The vapor retarder is required in your locale: http://www.buildingscience.com/docum...ecommendations

You may be able to substitute a vapor retarder primer paint (.45 perms) if local B.D. allows: http://www.panhandleinsulation.com/b...materials.html Batt facing (.4 - .7)

You may need R-38 in attic for your zip area: http://www.ornl.gov/sci/roofs+walls/...on/ins_16.html

If using batts and cellulose (.14 # per in.), with 7 inches to achieve the required R minus the batts = 1# per sq.ft. which will compress the batts somewhat, so add more or go cellulose all the way. BUT, if ceiling joists are 24"o.c. and plaster (8# per sq. ft.) you may very possibly overload it. http://www.bc.com/dms/wood/ewp/3_Gui...0Materials.pdf

Be safe, Gary

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Last edited by Gary in WA; 01-17-2010 at 09:29 PM.
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Old 01-18-2010, 02:08 PM   #3
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attic insulation-vapor retarder?


the studs are 16" o.c. how else can i lay a vapor retarder? should i cut plastic 15" wide and lay in between each stud? the house was built in 1920 and had minimal amounts of loose fiberglass insulation with no vapor retarder. the house seems fine to me.
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Old 01-18-2010, 02:28 PM   #4
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attic insulation-vapor retarder?


Don't use plastic (vapor barrier) when a vapor retarder will work: http://www.energysavers.gov/your_hom.../mytopic=11810

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Old 01-18-2010, 02:57 PM   #5
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attic insulation-vapor retarder?


so you think if i lay down r-15 for walls first, then blown in recycled stuff on top (an extra r-30) if would flatten the rolled insulation out too much to be effective?
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Old 01-18-2010, 10:54 PM   #6
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attic insulation-vapor retarder?


Cut a 12" square piece of cardboard and set it on the batt on the floor. Set a new water bottle, 16 oz., and 1/2 another one on top (if you can do that, people would pay). How much did it compress- 1 or 1-1/2" ? You might lose R-4 to R5-1/2. You could add more cellulose to make up for the compression, but that's not the point. You are compressing the batt, not just reducing the thermal value but making contact for heat loss through direct conduction because now it is touching with smaller air pockets which give glass batt the insulating quality. http://www.buildinggreen.com/auth/ar...me=140101a.xml

I would just paint a vapor retarder primer on the ceiling below, if required by Building Department, and blow-in cellulose, a whole lot easier than messing with the batts.

More importantly, have you air sealed yet? http://www.rd.com/how-to-seal-attic-...icle18158.html

Or check for a balanced venting system before you insulate? http://www.fureyco.com/content/image...ng_The_Air.pdf

Be safe, Gary

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