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Old 11-14-2019, 03:49 PM   #1
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Upgrade walls


I’m looking to re side my house. Also re sheath the exterior before siding. Is it worth changing the insulation in the walls while they are open? House was built in 1994. I believe it has R-11 in the 2x4 studs. Is it worth it to remove that and install roxul r-15? Thanks
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Old 11-14-2019, 04:09 PM   #2
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Re: Upgrade walls


Is there a reason for changing the sheeting too and about where do you live?
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Old 11-14-2019, 05:30 PM   #3
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Re: Upgrade walls


As noted a lot depends on where you are. Winery I am, you don’t build with two bye four exterior walls anymore, always two bye six for more insulation. Standard for two bye four is r11 using fiberglass.,, you can foam instead giving more r valu. You can add foam board to outside giving more r value....but a bigger pain in the butt relative to window and door moldings. Ron
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Old 11-15-2019, 04:36 AM   #4
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Re: Upgrade walls


I don't believe there have been any noteworthy advances in fiberglass batt insulation since the 90s (most of the advances there have been in ease of install as far as I've ever read) so I don't think it'd be worth replacing with fiberglass it unless the stuff in the walls is compacted or gotten wet or something.

Studies report that R15 is 73% more insulation than R11, but the rub is that's in best case scenarios of exactly equal walls for testing. The "consensus" on the street I've heard is that if you seal up the air gaps then R11 would be basically just as good and not worth the money to upgrade to R15.

I think that spray foam would be a better value for an upgrade because it not only seals a good deal of the air gaps automatically but also has a higher R value.

- And on spray foam, I wish I had gone with that when we had the majority of the back of our house open for our kitchen remodel; I went with replacing the 1978 fiberglass insulation. Not that I have complaints about the improvement per say, just that in hindsight it was the far better option.

Adding rigid foam insulation on the exterior (under the T1-11 siding) is something we do plan to do later and I think that might be an option worth considering rather than going from R11 to R15 - if you can make it work with your door/window frames of course.


As an additional thought, we put a house wrap (Tyvex in our case) on and it made a huge difference, even in areas where we didn't open up the walls to replace the insulation (like the front first story where we replaced the traditional cedar planking but didn't remove the sub-surface plywood.) I'd thought it was kind of a waste of time because we're down in a bit of a pit and don't get much wind, but I was wrong and the difference was easily noticeable. Its more than just a wind break heh
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Old 11-15-2019, 04:51 AM   #5
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Re: Upgrade walls


It really depends on your climate. But in general you may not see a significant return on increasing a 2x4 wall's R value with the batts. If you are exposing the walls, then that's your call on the pricey Rockwool. However, I would hazard a guess (without knowing why you are replacing the sheathing) that you will not be removing windows and doors, therefore not replacing the sheathing near them or being able to properly install the housewrap around them. So the main points of air infiltration at the wall penetrations will still have R11 and not be sealed in the most energy efficient manner anyway.
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Old 11-15-2019, 06:06 AM   #6
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Re: Upgrade walls


My old house was renovated, I think, late 70 or in the 80's. Not later. If yours is 1994, you may have r13. I have foil face r11 but the outside sheathing is 1x boards which are very leaky to air. As such, I am covering the outside with 1" xps foam boards, can foam, caulk or tape the joints, tar paper over for positive drain plane, then vinyl side.
If you are going for true thermal break, what I read is you need min 1.5" foam board. But I have doubts about vinyl siding nails hanging that much off the underlayment and not drooping. Just my guess. You probably have plywood sheathing and you don't necessarily have to add foam boards for air seal. The ply joints can be sealed, esp the foundation sill joint. My town inspector said added boards will count as a total system.
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Old 11-15-2019, 06:29 AM   #7
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Re: Upgrade walls


Quote:
Originally Posted by BanditParker View Post
Is it worth changing the insulation in the walls while they are open?
The cost of replacing the insulation for a 3 point increase in R value is never going to be justifiable.
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Old 11-15-2019, 09:20 AM   #8
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Re: Upgrade walls


I would suggest you go with the added layer of rigid (as mentioned) over the exterior and then strapping to give you a ventilation gap and a place to nail the siding. Once a wall becomes very well insulated that gap is necessary to help dry out condensation behind the siding.

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Old 11-15-2019, 03:26 PM   #9
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Re: Upgrade walls


Bud, if OP is in cold climate, would exterior foam need to be EPS to avoid having a double vapour barrier ?
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Old 11-15-2019, 03:58 PM   #10
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Re: Upgrade walls


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Bud, if OP is in cold climate, would exterior foam need to be EPS to avoid having a double vapour barrier ?
As long as the rigid foam does not have a foil or plastic covering it will have some permeability and allow some drying to the outside. One key is to be sure the foam is thick enough to keep the inside surface above the dew point, There are charts to help that decision.

However, adding 2" of foil faced rigid to the exterior is very common up here.

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Old 11-18-2019, 03:37 PM   #11
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Thanks guys. I’m in PA. Just outside of Philadelphia. The sheathing on the house is the crappy fiber boards. Black paper like material on front and back and then fiber on the inside. Swells and takes on the moisture. I have seen on one wall that it’s just sheathed with a foam board material. Not sure why there is a difference in sheathing. Could be that I’m seeing the fiber board in the attic and the the rest of the house is done the in the foam board. But no wood in sight. Birds made a few holes in the side and are nesting in the wall. So I can see the layers. I’ve also seen a few house in the block get resided. House warp is only used around the windows and doors. No where else. If I don’t replace the windows. I’ll at least be removing and reinstalling them. House is very drafty. I was considering the zip system with the insulation on the back side of it. Then no need to house wrap too.
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