# Rim joist insulation with 2" rigid pink foam



## french_guy (Sep 11, 2012)

I would like to insulate my rim joist with 2" pink foam
I'm planning to proceed as follow
1) caulk the perimeter of the cavities
2) cut the pink foam to leave a gap all around (gap = size of the foam spray nozzle)
3) Put some caulk on the back of the piece of foam to make it stick to the rim joist, making sure I have my gap all around
4) Put spray foam insulation by inserting the nozzle of the can inside that gap

What do you think? 
About the spray foam, should I use the regular Great Stuff, or the window foam that expand less?

Thanks


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## Windows on Wash (Aug 30, 2011)

The gap is just to make it easy to get the foam in place. You don't have to purposefully leave a gap if the rims are consistent in size. You can butter the openings with sealant and then just caulk the edges as well. 

Use the window and door foam (closed cell variant) if you are going to foam them in place. 

Either way, your plan looks solid.


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## Bud9051 (Nov 11, 2015)

If you are good at cutting, a press fit ends up being a lot faster. Where the foam likes a larger gap, using a caulk at the seams does well.

Check local codes to see if they will require the pink to be covered with an ignition barrier, like 1'2" drywall.

Bud


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## campbell804 (Sep 19, 2009)

Save some bucks and use the the "2 component spray system" they sell at HD and Lowes. It will cut your costs, rather then buying all the cans of "great stuff". Just make a little dolly to pull around the 2 propane like canisters. 


Soup


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## Windows on Wash (Aug 30, 2011)

campbell804 said:


> Save some bucks and use the the "2 component spray system" they sell at HD and Lowes. It will cut your costs, rather then buying all the cans of "great stuff". Just make a little dolly to pull around the 2 propane like canisters. Soup


It will definitely save you time. Not sure about the money part.


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## french_guy (Sep 11, 2012)

I don't mind the time.....I can do a few cavities here and there
I think the 2 can spray mix is messy
I will try the press fit and see if it's not too difficult to put it into the cavity
If too difficult, I guess I will go with my original plan


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## sbryant324 (Jan 27, 2016)

*Foam on Rim Joist*

The 2" will be a good start, sealing the edges, but be sure to run a bead along the top plate at the concrete as well. Rather than tanks, I bought larger cans that thread onto a gun. Far nicer to be able to shut off as well as having an accurate reach with a 12" tip. Put lotion on hands prior, even if wearing good gloves, faster cleanup... and be ready to write off any clothes you wear because the foam sticks to everything. Foam gives off a toxic smoke so as noted above if your code requires or not, it is best to drywall over it. I ran Roxul on top which is also fire resistant, to exceed R20.


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## french_guy (Sep 11, 2012)

I've done 3 cavities relatively quickly (2 large - 34 x 9 and 1 small - 6 x 9)
The foam cuts very well on my table saw...
I cut the foam as tight as possible. I caulked 1st the perimeter of the cavities, then install the foam and sealed with caulk again. Actually, I haven't used the spray foam....Is this OK?


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## Bud9051 (Nov 11, 2015)

That looks perfect, when are you coming over for my job . Can foam needs the gap idea you started with, but caulking does not and the caulking is much more forgiving when fingers are required.

A+

Bud
I do have a question for you, are you cutting that 2" in one pass with your table saw and if so what blade are you using. I have to cut 1" deep and flip it to avoid the blade grabbing the foam.

I have a small battery powered circular saw which runs at a much lower speed and it works great on foam, doesn't melt. Been wondering if I could slow my table saw down.

Thanks


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## french_guy (Sep 11, 2012)

"A+" sounds................French :wink2:

Yes, I cut the 2" thick foam in 1 pass
I'm using that blade:
http://www.amazon.com/gp/product/B0007CXBWU?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00
Mounted on a basic Ryobi table:
http://www.homedepot.com/p/Ryobi-15-Amp-10-in-Table-Saw-RTS10G/205216309

Cuts are very good (at least for my taste) and the foam is not melting at all 

I will do more cavities today, but will post pictures because I have deep ones going under a bay window (cantilever?). For now, there is some fiber glass, lay loose and randomly. Not sure what is the best way to proceed in that case.....!

@+


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## SeniorSitizen (Sep 10, 2012)

I would be leaving one to be removed on a cold ass winter day to check for rim joist condensation / moisture. In the 3rd picture of reply #8 there is an indication of previous moisture on the bottom edges of the joist.


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## french_guy (Sep 11, 2012)

Yeah, I saw it.....The previous insulation was fiber glass only, and it was kind of darkened in some places (condensation issue I guess?)
However my basement is not finished....

When I installed the foam, it was such a tight fit that even without the caulk, removing the board would mean breaking it !!!


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## Bud9051 (Nov 11, 2015)

Fiberglass insulation would have allowed warm air to pass through it to reach the cold rim joist and form condensation. If a fiber material is used it must be well air sealed and depending upon the climate possibly vapor sealed. But air is the primary transporter of moisture vapor.

I use a similar blade to the one you linked, but my rigid is the blue type. I haven't yet tried that rose colored and I'm not sure if it is formulated differently or not. I will be buying more so will try some. I'll get a new blade as well as this one is now coated with residue.

Thanks,
Bud


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## WhatRnsdownhill (Jan 13, 2016)

french_guy said:


> I've done 3 cavities relatively quickly (2 large - 34 x 9 and 1 small - 6 x 9)
> The foam cuts very well on my table saw...
> I cut the foam as tight as possible. I caulked 1st the perimeter of the cavities, then install the foam and sealed with caulk again. Actually, I haven't used the spray foam....Is this OK?


thats some nice n neat work....


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## Windows on Wash (Aug 30, 2011)

+1

Looks very clean. 

As Bud mentioned earlier, I would look at covering it with a ignition/fire barrier like fibrous insulation or drywall.


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## french_guy (Sep 11, 2012)

I've done 1 more cavity today....I find this pleasant (at least not unpleasant:vs_worry
Here are pictures showing the 3 steps: sealing the cavity, installing the foam and sealing the foam
I've asked the guy who did our inspection when we purchased the house 3 years ago, and covering the foam is not required by code
But I think i will put 3" Roxul anyway in each cavity


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## Bud9051 (Nov 11, 2015)

What are you using for caulking? 
Also wanted to mention, I use a Dewalt jig saw that holds the blade very straight and gets those cuts the table saw can't do, like L's. I clamp on a guide if I need really straight.


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## french_guy (Sep 11, 2012)

Bud9051 said:


> What are you using for caulking?
> Also wanted to mention, I use a Dewalt jig saw that holds the blade very straight and gets those cuts the table saw can't do, like L's. I clamp on a guide if I need really straight.


The white one to seal the foam is that one:
http://www.homedepot.com/p/DAP-Alex...lic-Latex-Caulk-Plus-Silicone-18103/100097524

The brown one to seal the cavity is an "old" can i had left....But now it's empty. So i will be using the white one from now
http://www.homedepot.com/p/DAP-Alex...lk-Plus-Silicone-12-Pack-7079818120/204839691


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## ProGreen (Oct 2, 2014)

french_guy said:


> "A+" sounds................French :wink2:
> 
> Yes, I cut the 2" thick foam in 1 pass
> I'm using that blade:
> ...


Great job! Looked through this thread and appreciate everyone's comments on your specifics.

Who manufacturers that rose colored 2" cc foam and what is its R rating?


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## ProGreen (Oct 2, 2014)

Also, what hand held saw cuts through 2" cc foam if you would? Thanks much.


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## french_guy (Sep 11, 2012)

It's "Foamular 150" from Owen Corning - I purchased mine at Home Depot
2" thick = R10
http://www.homedepot.com/p/Owens-Co...uared-Edge-Insulation-Sheathing-45W/100320352

Any saw with fine teeth will do fine I guess
I thought cutting on a table saw would be a mess, but it actually cut VERY well
I cut strips the height of my cavities (~8"3/4) and adjust the length with a hand saw. I'm using something like this (usually sold with the plastic miter box)
http://www.homedepot.com/p/Husky-14-in-Pro-Miter-Back-Saw-122MM14/204748835

Hope this help...


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## ProGreen (Oct 2, 2014)

Thanks for that. Looks as that would work, although may have to special order it at HD.


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## french_guy (Sep 11, 2012)

ProGreen said:


> Thanks for that. Looks as that would work, although may have to special order it at HD.


Have you checked at Lowes? 
There is also the blue foam, which is the same thing, but different brand....


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## Gary in WA (Mar 11, 2009)

"The data thus clearly demonstrates that it is not prudent from a condensation management perspective to fill the rim joists with batt insulation, regardless of whether they are covered with a vapor retarder or not. Free circulation of interior drying air in the rim joist cavity, particularly during the summer, would inhibit condensation as well as prevent moisture accumulation. Exterior insulation is effective in controlling winter rim joist condensation but tends to exacerbate summer condensation conditions, particularly in the presence of an interior vapor retarder. With the absence of interior batt insulation and an interior vapor retarder, the negative consequences of exterior rim joist insulation are mitigated. However, especially in retrofit situations, the amount of exterior insulation that can be installed (if any) may not be sufficient to provide adequate thermal insulation (at least R-10). Thus in these cases, the alternative is to install rigid insulation (such as* foil-faced* polyisocyanurate) flush against the interior side of the sheathing. This still allows air drying of the rim joist cavity but reduces the potential for interior summer condensation by decreasing the condensation surface to the bare minimum of the interstices of the insulation/ sheathing interface. In the winter, the insulation is protected from interior-sourced water vapor by the foil-facing.' Bold is mine, from; http://www.buildingfoundation.umn.edu/RimJoist/rimjoistphenom.htm

As the foam board moves from water intake/drying-temp changes, http://buildingscience.com/documents/published-articles/content/pa-foam-shrinks-correction/view possibly breaking your perimeter air seal, may want to add some poly now and air seal it as well. Hour-glass shape is best for movement; http://www.buildingdiagnostics.com/articles/sealant1.jpg 

Gary


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## Windows on Wash (Aug 30, 2011)

What do you suggest for ignition/thermal in this case if the basement is to be left unfinished?


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## Davejss (May 14, 2012)

I'd just spray foam it.


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## french_guy (Sep 11, 2012)

Gary in WA said:


> "The data thus clearly demonstrates that it is not prudent from a condensation management perspective to fill the rim joists with batt insulation, regardless of whether they are covered with a vapor retarder or not. Free circulation of interior drying air in the rim joist cavity, particularly during the summer, would inhibit condensation as well as prevent moisture accumulation. Exterior insulation is effective in controlling winter rim joist condensation but tends to exacerbate summer condensation conditions, particularly in the presence of an interior vapor retarder. With the absence of interior batt insulation and an interior vapor retarder, the negative consequences of exterior rim joist insulation are mitigated. However, especially in retrofit situations, the amount of exterior insulation that can be installed (if any) may not be sufficient to provide adequate thermal insulation (at least R-10). Thus in these cases, the alternative is to install rigid insulation (such as* foil-faced* polyisocyanurate) flush against the interior side of the sheathing. This still allows air drying of the rim joist cavity but reduces the potential for interior summer condensation by decreasing the condensation surface to the bare minimum of the interstices of the insulation/ sheathing interface. In the winter, the insulation is protected from interior-sourced water vapor by the foil-facing.' Bold is mine, from; http://www.buildingfoundation.umn.edu/RimJoist/rimjoistphenom.htm
> 
> As the foam board moves from water intake/drying-temp changes, http://buildingscience.com/documents/published-articles/content/pa-foam-shrinks-correction/view possibly breaking your perimeter air seal, may want to add some poly now and air seal it as well. Hour-glass shape is best for movement; http://www.buildingdiagnostics.com/articles/sealant1.jpg
> 
> Gary


So to summarize, is what I did wrong/bad?


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## Gary in WA (Mar 11, 2009)

No, you're ok... just you may get some interior based moisture from the floor cavity, just like a wall cavity except yours is 5 times longer in a floor than 8' tall wall. ADA the drywall in the basement, when finishing as the room air (possibly containing moisture, will go right through any fibrous insulation and condense on the foamboard if that cavity insulation is thick enough to lower the dew-point there. Exterior solar drive could send moisture/vapor into the rim joist and wet the foam which takes longer to dry, depending on many factors. With ff (or plastic) on each side, you stop any moisture from either side. Maybe you don't need to worry about it... read the moisture content test readings in that link.... for that particular location. Always helps if you have 1-2' of exterior exposed concrete to dry the wet concrete below grade as you are driving the walls moisture up if easier than through the foamboard, through capillarity, giving a much wetter mudsill plate/rim; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code

Gary


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## Windows on Wash (Aug 30, 2011)

french_guy said:


> I've done 1 more cavity today....I find this pleasant (at least not unpleasant:vs_worry Here are pictures showing the 3 steps: sealing the cavity, installing the foam and sealing the foam I've asked the guy who did our inspection when we purchased the house 3 years ago, and covering the foam is not required by code But I think i will put 3" Roxul anyway in each cavity



From Fomular's site...

Q: Can FOAMULAR® be left exposed in a basement wall application?

A: No. To comply with building codes, all foam plastics must be covered with a 15 minute thermal barrier. Gypsum board, ½” thick is a common covering.

http://www.foamular.com/foam/faqs/#appgen



There is a variance and grey areas in what folks interpret as a wall vs the rim, but I would check with code officials in your area and get it I writing if I were you. 



https://www.insofast.com/ux-panels/installation/rim-joist


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## Gary in WA (Mar 11, 2009)

The 3" Roxul you have planned will probably work (ask local AHJ) for the ignition barrier, per codes (1-1/2" fibrous insulation) 316.5.11-interpreted by your local AHJ;http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_3_sec016.htm?bu2=undefined

BSC recognizes this can usually be left uncovered (in SPF slightly different than rigid board);http://buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist

Some foams are of a higher fire/smoke rating than others, end result; satisfy- the building officials and more importantly your HO Insurance carrier (and family safety); http://www.greenbuildingadvisor.com...mal-barriers-and-ignition-barriers-spray-foam

Remember to caulk the wood rim before adding the foamboard;* Post #8* here; http://www.diychatroom.com/f103/insulating-rim-joist-caulk-spray-foam-around-edges-168849/

Gary


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## lem6611 (Sep 2, 2018)

french_guy said:


> I would like to insulate my rim joist with 2" pink foam
> I'm planning to proceed as follow
> 1) caulk the perimeter of the cavities
> 2) cut the pink foam to leave a gap all around (gap = size of the foam spray nozzle)
> ...


Hi:

I am doing the same project in my basement. First long piece of Pink FOam board, i used too much Great Stuff and it pushed out the pink board in some spots. So back to the starting board. My question....if I cut the foam board leaving only a smallish gap around all sides, does the caulking work best, like you did? Where I think I made an error was trying to fill the entire gap with Great Stuff (1.5" inches deep as I used 1.5" foam board) rather than just seal the gap. Hope that makes sense. So just wanted to see if when you caulked, you just sealed the outside gap, and didn't worry about getting caulking into the whole 1.5" gap area.

Thanks.


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## french_guy (Sep 11, 2012)

lem6611 said:


> Hi:
> 
> I am doing the same project in my basement. First long piece of Pink FOam board, i used too much Great Stuff and it pushed out the pink board in some spots. So back to the starting board. My question....if I cut the foam board leaving only a smallish gap around all sides, does the caulking work best, like you did? Where I think I made an error was trying to fill the entire gap with Great Stuff (1.5" inches deep as I used 1.5" foam board) rather than just seal the gap. Hope that makes sense. So just wanted to see if when you caulked, you just sealed the outside gap, and didn't worry about getting caulking into the whole 1.5" gap area.
> 
> Thanks.


Hi
I cut the foam as tight as I could, and just caulked the 4 sides....That's it
Didn't try to "push" the caulk deep inside


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## Bud9051 (Nov 11, 2015)

If you make the gap the width of the straw on the can you can reach all the way in and apply just a bead of foam. I use the gun that delivers a more controlled bead. The cans are kind of on or off.

Which type of can foam are you using, window and door, regular, or gaps and cracks. The last two expand a LOT. The low expansion window and door still expands but much less.

You can also apply a bead of caulking picture frame style before you insert the rigid. Then apply another bead before the next layer of foam or to finish it off.

Once you have played with the can foam you gain a better understanding about the mess it makes. Caulking is much more user friendly.

As a last resort there is a zero expanding foam, DAP. I don't consider it a rigid as the Great Stuff, but on 6" deep windows I like to foam it once and be done.

Bud


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## lem6611 (Sep 2, 2018)

Thanks so much for the quick reply! You answered exactly the question I was trying to illustrate---if I needed to fill the entire gap with caulk. I did seal the inside of the "box" with caulk before I had inserted the pink foam board, so at least I did one thing right!

I appreciate again you taking the time to respond. Take care.


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## lem6611 (Sep 2, 2018)

Hi Bud:

Thanks for the reply. I had used the regular Great Stuff expanding foam. It wasn't the type to fill big gaps, just the ordinary red can. I had cut the pink board 1/2 smaller the whole way around to provide enough gap, but like my first post said, I think my fatal mistake was pushing the foam all the way to the back and only stopped when it started to spill out of the front and sides. When I pulled off the foam board today, while there was a very nice seal on the top, what happened is about 1/4" down from the top at the back, foam got behind the pink board (remarkably, only about 3/16) and slightly pushed out the foam board, which allowed me to actually deflect the board and even broke the bead of Alex Plus caulking I put at the bottom. I was going to try and use 2 1/2" Grip Rite cap nails to nail the newly created hollow spot out, but worried that this could cause moisture problems that I'd never see once I frame out and drywall the walls.

Sounds like my best option when I re-cut the new pink board is to cut as tight as possible and then run a bead of Alex Plus caulking around the perimeter??

Thanks again Bud for your input and information. Take care.


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## lem6611 (Sep 2, 2018)

Hi Bud. One last question....when you said "You can also apply a bead of caulking picture frame style before you insert the rigid. Then apply another bead before the next layer of foam or to finish it off." I was a bit unclear of the progression. I did apply originally the caulking around the inside perimeter of the joist rim box before putting the foam board in. After this, much like the French Guy did, I was not going to try and fill the gap completely with caulking or expanding foam, but just seal the exterior perimeter of the foam board. Would this be an acceptable option in lieu of filling the entire gap up with Great Stuff? I just wasn't sure when you mentioned about applying another bead of caulking before the next layer of foam. Hope this makes sense. Thanks for you insights!


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