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Old 04-23-2020, 08:18 PM   #1
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“Flash and Batt” with RMaxx board and Roxul


We are remodeling a home we bought several years ago and have decided to build a “double wall” along the exterior of the home. Original wall studs are rough cut 2”x4” lumber. I wanted to get some more R value in the walls and avoid having to remove the 50,000 lathe nails from the studs, so we built a 2x4 wall 1/2” inside the existing exterior walls. I have access to unlimited scrap pieces of “Rmaxx” board (2” Closed cell foil faced foam board) as well as access to kits of Fomo 2Part Spray Foam.
I am installing 1 piece of 2” Foam board into the exterior wall and then air sealing it with the 2 part spray foam. Once the exterior walls are sealed I want to run our blower door assembly and see what kind of air leakage remains, before installing our Roxul ComfortBatt R15 in our newly built 2x4 walls.
I also staggered the new studs so I could hopefully hit the old existing studs with some 2 part to help with thermal bridging. Anyone see any issues with this install??? One thing I have worried about it the possibility of condensation on the inner side of the Foam board, it is R-13.1 at 2” thickness. The spray foam will not be giving the Board any more Rvalue, it will just be used to air seal.
Home is located in Northern Pennsylvania so Cold winters down below 0 and hot summers sometimes above 100°.
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Old 04-23-2020, 10:30 PM   #2
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Re: “Flash and Batt” with RMaxx board and Roxul


Looks fine. What kind of exterior sheathing? Ply or boards? Neither the foam boards nor the spray foam comes with air seal guarantee. I read in the forum that foam materials will shrink over time and may separate from framing materials. So if ply, I would take the extra step of caulking all stud bay and plywood joints. Boards can't be sealed this way since many of them also have cracks, knots. We do the best we can, but don't expect air tight seal.

When installing drywall, air seal between floor sill plate and drywall. Seal the electric/switch/cable boxes and the drywall gaps.



About the foam boards. You're using scraps, free or discount? Since using extra spray foam, does it look like still a value? I've seen scraps advertized but the ones I saw were small enough to need 3-4 per stud bay.
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Old 04-24-2020, 04:38 AM   #3
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Looks fine. What kind of exterior sheathing? Ply or boards? Neither the foam boards nor the spray foam comes with air seal guarantee. I read in the forum that foam materials will shrink over time and may separate from framing materials. So if ply, I would take the extra step of caulking all stud bay and plywood joints. Boards can't be sealed this way since many of them also have cracks, knots. We do the best we can, but don't expect air tight seal.

When installing drywall, air seal between floor sill plate and drywall. Seal the electric/switch/cable boxes and the drywall gaps.



About the foam boards. You're using scraps, free or discount? Since using extra spray foam, does it look like still a value? I've seen scraps advertized but the ones I saw were small enough to need 3-4 per stud bay.
Sheathing is old board, not ply, so there’s no way to really seal that with any sort of caulking. All the scrap pieces are free of charge to me. It’s crazy the amount of board that companies waste. They cut a 16”x16” piece out of a 4’x8’ sheet and they toss it so most pieces are almost full sheets. I’m ripping them down on table saw so most bay will have 2 pieces, 3 tops.
I also have the luxury of time during this project so that’s why I’ll run some blower door tests once the exterior is done to see if anywhere did shrink up. It’s been my experience, if you clean away the dust and debris from the wall before you spray, it helps deter shrinkage.
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Old 04-24-2020, 06:22 AM   #4
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Re: “Flash and Batt” with RMaxx board and Roxul


" It’s crazy the amount of board that companies waste." Same with drywall and maybe because they are charging by the number of sheets and they don't want to waste their time saving the customer money. Just be sure all pieces are sealed together, I like construction adhesive for sealing, I've seen it after several years and still well attached.

Do you have an infrared camera to go with that blower door? The actual leakage number is far less significant than seeing where that leakage is.

Bud
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Old 04-24-2020, 06:25 AM   #5
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" It’s crazy the amount of board that companies waste." Same with drywall and maybe because they are charging by the number of sheets and they don't want to waste their time saving the customer money. Just be sure all pieces are sealed together, I like construction adhesive for sealing, I've seen it after several years and still well attached.

Do you have an infrared camera to go with that blower door? The actual leakage number is far less significant than seeing where that leakage is.

Bud
Yes I have access to a Flir fun that is pretty cool to use. The Foam Board is actually holding nicely to the sheathing just by the old nails sticking in. Anywhere I need to, I have been adding screws or nails to hold it in place. The 2 part pray foam will also bind the pieces together once I get everything sprayed.
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Old 04-24-2020, 06:38 AM   #6
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Re: “Flash and Batt” with RMaxx board and Roxul


To avoid the blower door setup you can use a large window fan, it only needs to be strong enough to overcome the stack effect exfiltration in the upper part of the house and that doesn't take a lot of air. It is the IR camera that does the hard wok. Every once in awhile you can use the blower door to get a leakage number to track your progress, but for leak detecting a big window fan will do.

I have visited some well insulated homes and they are amazing, I also live in one (in progress) and there are times when the furnace not coming on that I have to check, like below zero with wind and no furnace cycle for almost an hour. My extra insulation went on the outside, 2 layers so good air seal.

Best,
Bud
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Old 04-24-2020, 06:45 AM   #7
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To avoid the blower door setup you can use a large window fan, it only needs to be strong enough to overcome the stack effect exfiltration in the upper part of the house and that doesn't take a lot of air. It is the IR camera that does the hard wok. Every once in awhile you can use the blower door to get a leakage number to track your progress, but for leak detecting a big window fan will do.

I have visited some well insulated homes and they are amazing, I also live in one (in progress) and there are times when the furnace not coming on that I have to check, like below zero with wind and no furnace cycle for almost an hour. My extra insulation went on the outside, 2 layers so good air seal.

Best,
Bud
That’s what we are hoping for Bud!!! Especially in our area where winters get frigid and windy, it would be nice to not here the boiler running constantly. I figured spending the time and material now will be a good investment down there road
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Old 04-24-2020, 07:52 AM   #8
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Re: “Flash and Batt” with RMaxx board and Roxul


Lots of pictures. Unfortunately future buyers don't really understand super insulation so being able to show them pictures plus the lower heating costs can get you a better price.

I inspected a small home here in my town that had board siding along with plaster and lath. Leakage to the inside was very minimal, but heating costs were very high. Then i asked what was used for sheathing. In a storage area we could see the boards with their 1/4" gaps and daylight as the siding was old cedar shakes. Although the air was not leaking into the house the air flow into and out the exterior wall assembly was extreme and he basically had zero insulation value.

Since he was going to replace the siding anyway, he added 2" of rigid blue foam board. Taped and sealed he finally got the results he was looking for.

BTW, 3' of insulation in the attic and 6" of spray foam on basement walls, he had tried but failed and that is why I got the call.

Bud
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Old 04-24-2020, 08:27 AM   #9
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Lots of pictures. Unfortunately future buyers don't really understand super insulation so being able to show them pictures plus the lower heating costs can get you a better price.

I inspected a small home here in my town that had board siding along with plaster and lath. Leakage to the inside was very minimal, but heating costs were very high. Then i asked what was used for sheathing. In a storage area we could see the boards with their 1/4" gaps and daylight as the siding was old cedar shakes. Although the air was not leaking into the house the air flow into and out the exterior wall assembly was extreme and he basically had zero insulation value.

Since he was going to replace the siding anyway, he added 2" of rigid blue foam board. Taped and sealed he finally got the results he was looking for.

BTW, 3' of insulation in the attic and 6" of spray foam on basement walls, he had tried but failed and that is why I got the call.

Bud
We are planning to live here for a while once we are done so this work will only benefit us. I agree that most people would have no clue what they were looking at when I showed them pictures, all most people care about is the “finished product” They don’t care that the exterior walls are empty and air leakage is everywhere as long as the kitchen cabinets look nice Hahahaha.
Fortunately I also have access to cellulose insulation as well as a machine to blow it in so the attic will be getting LOTS of insulation, that is of course AFTER we air seal everything.
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Old 04-24-2020, 09:42 AM   #10
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Re: “Flash and Batt” with RMaxx board and Roxul


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One thing I have worried about it the possibility of condensation on the inner side of the Foam board, it is R-13.1 at 2” thickness. The spray foam will not be giving the Board any more R value, it will just be used to air seal.
Around here (Southern Ontario), I have seen 1" R6.5 board used. It must be allowed, but I am of the opinion that it is too thin. R13 should be good. I have seen it charted (on the internet) for R value required to avoid interior condensation. I don't remember where I saw it so I will leave it to you to try to search out where that is posted.

One thing to keep in mind is making a tight fit where you are joining pieces together. If you have a 1/2" gap between boards, and spray foam over it to air seal, then you have a small area with only maybe R 3. I am not sure how that would effect any possibility of condensation.
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Old 04-24-2020, 10:52 AM   #11
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Re: “Flash and Batt” with RMaxx board and Roxul


Most of those charts have ended up behind membership walls, but here is one still available for a few visits.
https://www.finehomebuilding.com/201...-exterior-foam

Bud
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Old 04-25-2020, 12:27 PM   #12
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Re: “Flash and Batt” with RMaxx board and Roxul


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Originally Posted by Bud9051 View Post

Since he was going to replace the siding anyway, he added 2" of rigid blue foam board. Taped and sealed he finally got the results he was looking for.

BTW, 3' of insulation in the attic and 6" of spray foam on basement walls, he had tried but failed and that is why I got the call.

Bud

When you add 2" to the exterior, what do you do about windows? Do you remove them and add the foam and the reset them? Do you have to recase the inside of the windows?

Last edited by APA; 04-25-2020 at 12:42 PM.
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Old 04-25-2020, 02:44 PM   #13
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Re: “Flash and Batt” with RMaxx board and Roxul


This article may answer your question. They offer a free trial to see the whole article.
https://www.greenbuildingadvisor.com...-outie-windows

And this link:
https://www.buildingscience.com/docu...-can-be-a-pain

I did mine as innies so created a new rough opening with new sheathing, installed the new construction with the flange, and then housewrap and siding. Windows had built-in J-trim.

Bud
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