re-insulating exterior wall from outside


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Old 02-14-17, 02:34 PM
T
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re-insulating exterior wall from outside

I am looking to have new windows and siding installed at my home in Omaha NE, and would also like to re-insulated as well. This is the process i am looking to do:

1. Remove siding/sheathing. (same thing on my home)
2. Remove old bat insulation.
3. Install plastic vapor vapor barrier against drywall between studs. (is this even necessary)
4. Install Roxul
5. Reinstall sheathing
6. Install house wrap
7. Install insulated siding (supposed to help with thermal bridging, is it worth the extra cost?)

Please let me know if anything can be added/removed from this list.

Thanks-
 
  #2  
Old 02-14-17, 02:58 PM
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Rather than install insulated siding, consider installing rigid foam over the sheathing:

How to Install Rigid Foam Sheathing | GreenBuildingAdvisor.com
 
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Old 02-14-17, 03:31 PM
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What is wrong with the existing fiberglass insulation?
If it is there it has r-value and removing it to add Roxul (although I like Roxul) has minimal payback. That effort and money could be put into a lice layer of rigid over the sheathing and then new siding, skip the insulated siding. Many articles about installing a layer of rigid on the outside as CT suggests.

Personally, I installed 3.5" of rigid from above the top plate to the foundation. I framed the windows with 2x and then added another layer of sheathing (optional with 2" of foam. The exterior layer of rigid is continuous and covers the rim joist and top plate. Then you install new construction windows with new flashing. There are some important details I haven't mentioned, but the current fiberglass can probably stay.

Bud
 
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Old 02-15-17, 07:40 AM
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I'm looking to avoid having the build the windows out for the foam, so i'm looking for other options.

I did a bathroom remodel a couple years back where i had to remove the drywall on the exterior wall. I noticed that the existing batts (didn't seem to be fiberglass; rock wool?) only filled about half of the wall cavity.
 
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Old 02-15-17, 07:56 AM
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I'm looking to avoid having the build the windows out for the foam, so i'm looking for other options.
Don't know what to say about this; insulation takes mass and space.
 
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Old 02-15-17, 08:10 AM
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That is completely understandable, but i'm attempting to balance cost/labor/effectiveness. The current wall assembly is not insulated very well at all; i'm just looking to improve it without breaking the bank. I guess the main questions i have are whether or not retroing a vapor barrier is even worth the hassle and if insulated siding would be a decent alternative to doing a full rigid foam install
 
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Old 02-15-17, 08:10 AM
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Building the windows out is actually easy, and especially easier than replacing the sheathing.
A wall assembly with r-11 insulation would be derated to about r-8 due to thermal bridging and incomplete fill. Replacing that with r-15 Roxul (also derated due to thermal bridging, R-13)would be about a 50% improvement. But, leaving the assembly as is and covering it with 2" of polyiso at r-6.5 per inch (r-13) (do derating for bridging) would be a 150% improvement to about r-21. Plus the exterior application will be covering all the way down to the top of the foundation.

Bud
 
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Old 02-15-17, 08:13 AM
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The insulated siding is 90% marketing. Best application for it is when you need to help smooth out what is under it. but for adding insulation value, vinyl siding lets the air flow right through, it is a rain coat, not a warm jacket.

Bud
 
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Old 02-15-17, 10:57 AM
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does this sound better

1. Remove and save siding/sheathing. (same thing on my home 3/4 plywood)
2. Remove old batt insulation.
3. Install plastic vapor vapor barrier against drywall between studs. (is this even necessary)
4. Install Roxul
5. Reinstall sheathing
6. block around windows with 1x4 to make up for foam
7. Install windows and house wrap (need to figure out jamb extentions to make up for the foam
8. Install 3/4" or 1" polyiso
9. Install siding
 

Last edited by TheQuiz; 02-15-17 at 11:43 AM.
 

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