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Foil faced fiberglass insulation question vs craft paper

Foil faced fiberglass insulation question vs craft paper


  #1  
Old 12-18-10, 04:11 AM
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Foil faced fiberglass insulation question vs craft paper

Hey all,
I need your advise. I will be building a house and want to know if it is better to use craft or foil faced R11 glass. It is 2x6 walls with 2" spray foam and R11 in the cavities. The exterior will have 1" iso board over the sheething, under the vinyl siding, to help prevent telegraphing of heat thru the studs. I don't want to use all spray foam in the cavities in case in the future you have to snake wires thru for something you forgot!
What do you think???
 
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Old 12-18-10, 10:23 PM
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This will get you started: Calculating the Minimum Thickness of Rigid Foam Sheathing | GreenBuildingAdvisor.com

No foil-faced anywhere on your wall, no OSB, no polyiso, use a house wrap, no low density R-11, use a sill sealer, plate caulking, ada (airtight drywall approach), studs 2' on center- if allowed, etc, etc........

Gary

Gary
 
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Old 12-19-10, 03:11 AM
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Thanks for the reply but I still have the same question. Some of the things you said are common sense, but no osb, 2' OC studs? What IBC allows this????? The link you sent is all well and fine but what happens when you try to nail siding to thick foam, it will sag and get wavey. How do you treat your door and window jambs, have everything custom made? Standard jam for 2x6 is 6 9/16". Fir up everything and use 4" nails?? I won't even ask about a hot roof.........
 
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Old 12-19-10, 05:54 AM
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Why are you selecting that construction method? Is it permitted by code? And if so, the building plans should cover the other how to issues.

Bud
 
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Old 12-19-10, 01:49 PM
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OSB lets moisture through slowly: BSI-038: Mind the Gap, Eh! — Building Science Information

SPF is not recommended against OSB: http://www.earthane.com/ctu32e.pdf

Use a house wrap, don't rely on the foam board as a WRB: Using Rigid Foam As a Water-Resistive Barrier | GreenBuildingAdvisor.com

The R-11 is a low density batt that can get convective loops inside it from heating the cavity: There's more to insulation than R-value | New Life Journal | Find Articles at BNET
It will be difficult to install the SPF with a smooth surface in the cavity to get full contact of the fiberglass insulation without any air spaces that give convective loops. Info-501: Installation of Cavity Insulation — Building Science Information

The 2’ on center framing is called “Advanced” (ask local B.D.) and saves energy: Green building & remodeling for dummies - Google Books

Advanced Energy

Add up the edge thickness of all the studs you will have R-8 on; example= 30’ wall = +- 23 studs x 1-1/2 = 34-1/2”----- almost 3’ of R-8 in a 30’ wall, 1/10th, 2’o.c. = 16 x 1-1/2” = 24” or 10”less for one wall, insulated at the higher R-value times each wall in the house.
The 2'o.c. may not work with vinyl siding, (my last choice along with fiberglass insulation).

Gary
 
 

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