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Old 11-26-2011, 08:56 AM   #1
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Total R-VALUE


Have a home built in the 50's. Need to upgrade the insulation in the attic. Have the blown in kind up there right now, just level with the joist. I know I need like a R-49 value. Question I have is do I include what's up there now plus another R-value to get to R-49? Thanks.

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Old 11-26-2011, 09:13 AM   #2
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Total R-VALUE


Your R-value is just a simplistic value used in a the codes and not the real insulation value of the floor, roof or wall wall system. the r-value referred to is the manufacturers ideal value for a short term laboratory test.

If you have 4" ceiling joints at 16" o.c., with R13 insulation between and up to the top of the joist, the real value would be between R9 and R11. If you have 6" joists at 16" o.c. with R19 up to the top of the joist, the real value would be between R13 and R16, to be generous.

You can legally add the R-values of the layers in pancake style. the extra fluff will not decrease air infiltration of loss.

You will probably not be inspected other than a quick look without any disturbance.

Make sure the new insulation does not obstruct any areas used for air intake and finally discharge through either ridge vents, box vents or eave vents.

Dick

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Old 11-26-2011, 09:26 AM   #3
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Total R-VALUE


Thanks for the info. What about the sofit area. There is no insulation in there now......keep it out? (Just by the ones with a vent) Thanks.
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Old 11-26-2011, 12:21 PM   #4
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No need to insulate the soffit area. You may want to add ventilation at some time. You can buy foam or cardboard chute to provide an open flow of the exterior air. through the unconditioned attic space and out through the upper exhaust vents to keep the attic air as close as possible to the outside air.

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Old 11-26-2011, 12:25 PM   #5
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You need to apply soffit vent chutes prior to the blown in insulation.

Seal all the top plates and penetrations first.

http://www.heritagebuildersmenomonie...ficiency_5.jpg

http://www.google.com/url?sa=t&rct=j...wDDqXuo3HsPlOQ
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Old 11-26-2011, 01:43 PM   #6
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Quote:
Originally Posted by Windows on Wash View Post
You need to apply soffit vent chutes prior to the blown in insulation.

Seal all the top plates and penetrations first.

http://www.heritagebuildersmenomonie...ficiency_5.jpg

http://www.google.com/url?sa=t&rct=j...wDDqXuo3HsPlOQ
Do I need to install vent shoots in every sofit well like thew pic or just the ones that have a sofit vent to outside? Thanks.
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Old 11-26-2011, 06:55 PM   #7
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Everyone.

Vent chutes help control the wind wash of insulation as well to preserve the R-Value
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Old 11-29-2011, 10:54 AM   #8
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Total R-VALUE


Is there a difference in R-Value for using foam insulation? For example let's just say it's recommended for a crawlspace to have an R-Value of 19. Is that R-19 Value regardless of what type of insulation you use or would you need a lower R-Value say if you were using Closed Cell Foam? Is there a different guideline or charts to follow if using foam insulation vs. traditional fiberglass? Thanks in advance!
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Old 11-29-2011, 04:55 PM   #9
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Total R-VALUE


R value is r value as I understand it, however r value does not account for drafts. So you'd need to use the same r-value of closed cell but closed cell usually does a better job at stopping drafts so you'd see further gains in that department
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Old 11-29-2011, 07:16 PM   #10
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R-Values are dependent on air movement and temperature differential (which drive air movement).

Example - an applied R-Value of foam will remain relatively constant (minus some measured degradation over time) because there is not air movement inside the foam.

Rigid foam is going to be your best bang for the buck in your application.

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