# Rim joists insulation advice



## Nealtw (Jun 22, 2017)

Should have been done before the wall was installed and I don't see fire stop either.


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## mishenka (Jan 7, 2021)

@Nealtw and I agree with you. Asking for any way to rectify it now or minimize the adverse effects having some areas not insulated (well, there is a fiberglass insulation anyway). As far as firestops - I called local town inspector and he said that since I am not drywalling ceiling there is no need/requirement for firestops at all. Nevertheless I intent to do horizontal firestops along the walls. So, any advice? Or, at least, what actually should have been done before I installed the walls that run parallel to joist rims, please?


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## Nealtw (Jun 22, 2017)

mishenka said:


> @Nealtw and I agree with you. Asking for any way to rectify it now or minimize the adverse effects having some areas not insulated (well, there is a fiberglass insulation anyway). As far as firestops - I called local town inspector and he said that since I am not drywalling ceiling there is no need/requirement for firestops at all. Nevertheless I intent to do horizontal firestops along the walls. So, any advice? Or, at least, what actually should have been done before I installed the walls that run parallel to joist rims, please?


Fire stop is not needed if you are not finishing the ceiling. We could never frame with the idea we could predict the future. Block between studs on the outside wall is not enough.
TGI flooring system has knock out holes for wires and pipes, I suspect you could spray foam thru those holes.


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## mishenka (Jan 7, 2021)

Yes, I did use those holes to run wires. But there is (I suspect, I just don't recall now) a fiberglass pieces of insulation as you can see in the rim joist cavities on the other wall. I'd be spraying over it - would that be ok? I really don't know how that foam works. What about the rim joist that are still fully accessible and currently have the fiberglass shoved in there - do I leave it there? do I remove and replace with .. something else and seal?

ok, about firestop. I still can fully do the firestop. As I said I spoke with the inspector and he confirmed that what I wanted to use for the fire stop totally works. I planned on using mineral wool insulation to put at the top of each stud cavity for the horizontal fire blocking. Wasn't sure how tall of a strip would be needed - 10 - 15 inches? The rest of the stud cavity would be filled with regular fiberglass insulation. If financials were unlimited - I'd simply use mineral wood top to bottom around the basement. That would be an insulator and fire stop at the same time. But... $ is limited So, do you agree that I can still do the fire prevention procedures which are fully compliant to the code?


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## Nealtw (Jun 22, 2017)

So you don't know if there is insulation there now?

It is the space between the wall and the foundation that inspectors worry about here.


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## mishenka (Jan 7, 2021)

How would I be able to do that with this setup? Floor joist is practicallt touching that wooden strip where insulation is secured. I couldn't have put any barrier there. What would be a solution - taking down the entire insulation layer and rehanging it lover to accommodate for an OSB (or whatever should be used) for fire prevention?


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## mishenka (Jan 7, 2021)

Nealtw said:


> So you don't know if there is insulation there now?


I honestly don’t recall right now I’ll check - there are places I can see, a bit later when I return home. But I tend to believe there must be insulation, I just can’t imagine builder insulting one wall and not the other.


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## Nealtw (Jun 22, 2017)

mishenka said:


> I honestly don’t recall right now I’ll check - there are places I can see, a bit later when I return home. But I tend to believe there must be insulation, I just can’t imagine builder insulting one wall and not the other.


Some builders supply insulation for framers to put in and some don't, many cavities can be left open in a house when no one cares when it is being built.


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## Nealtw (Jun 22, 2017)

mishenka said:


> How would I be able to do that with this setup? Floor joist is practicallt touching that wooden strip where insulation is secured. I couldn't have put any barrier there. What would be a solution - taking down the entire insulation layer and rehanging it lover to accommodate for an OSB (or whatever should be used) for fire prevention?
> View attachment 639692


Your joists are sitting on a sill plate. I don't know what you are suppose to do with that bag. 
Here all our outside walls are built insulated and drywalled with VB as part of the build. So home owners don't have to deal with it.


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## mishenka (Jan 7, 2021)

@Nealtw SIr, I can confirm there is insulation in every rim joist cavity. I have an unfinished closet are with one wall that runs parallels to the floor joist - it's clearly there. I also checked those walls where I already built the walls - there are gaps at the top I can see through. Insulation is there. First pic.

Second picture shows a view from the top in one of the rim joists. So, correct me if I am wrong, proper fireblocking would include covering the gap that runs between the sil plate (where the white fiberglass is now) all the way to the frame I built, correct?

That's a good thing that wherever you are the builder usually does all of that. Where I am - this is what I get as far as the basement goes. It is what it is and it's my job to do it assuming I want to. And I do want to. I truly enjoy building and learning from experienced people like yourself. Hope you don't mind sharing your knowledge and advice. Thank you so much.


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## Nealtw (Jun 22, 2017)

mishenka said:


> @Nealtw SIr, I can confirm there is insulation in every rim joist cavity. I have an unfinished closet are with one wall that runs parallels to the floor joist - it's clearly there. I also checked those walls where I already built the walls - there are gaps at the top I can see through. Insulation is there. First pic.
> 
> Second picture shows a view from the top in one of the rim joists. So, correct me if I am wrong, proper fireblocking would include covering the gap that runs between the sil plate (where the white fiberglass is now) all the way to the frame I built, correct?
> 
> That's a good thing that wherever you are the builder usually does all of that. Where I am - this is what I get as far as the basement goes. It is what it is and it's my job to do it assuming I want to. And I do want to. I truly enjoy building and learning from experienced people like yourself. Hope you don't mind sharing your knowledge and advice. Thank you so much.


So much is different in different places 
When we build we install 2 sill plates on the concrete wall and the top one is a 2x10, the 2x10 is the fire stop for that wall. It is also an air stop because you don't want house air getting to a cold surface.


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## mishenka (Jan 7, 2021)

Wow, it is different. What if I put something like 3/4 (playwood? osb? what would you recommend?) as indicated in black outline on the drawing? Alternatively I can put, as he local inspector agreed, rookwool material right on top of that gap (or gaps, to be precise).

Of course it will only take care of the walls where rim joists are still exposed. Since now I know for sure that there is fiberglass insulation in the areas that are covered by the framing (my fault for not thinking before) - would pouring foam or any oher type of sealant even work? What would be your recommendations to rectify my screw up? It is not only about fireblocking, which I don't need to do by code, but more about preventing air hitting the cold concrete walls.


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## Nealtw (Jun 22, 2017)

mishenka said:


> Wow, it is different. What if I put something like 3/4 (playwood? osb? what would you recommend?) as indicated in black outline on the drawing? Alternatively I can put, as he local inspector agreed, rookwool material right on top of that gap (or gaps, to be precise).
> 
> Of course it will only take care of the walls where rim joists are still exposed. Since now I know for sure that there is fiberglass insulation in the areas that are covered by the framing (my fault for not thinking before) - would pouring foam or any oher type of sealant even work? What would be your recommendations to rectify my screw up? It is not only about fireblocking, which I don't need to do by code, but more about preventing air hitting the cold concrete walls.
> 
> View attachment 639721


The cover in the drawing would work, 1/2 plywood, OSB. sheetrock or 2x are okay here. 
The side with no access would only give access to the one cavity in the floor system, not as much as the wall that could spread fire right across the floor.


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## mishenka (Jan 7, 2021)

Though not a fire prevention approach - I can, after securing drywall, (or even before?) apply airtight sealant where indicated with white on the image. Is that a reasonable approach to prevent hotter air from inside the basement reaching cold cement wall?


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## Nealtw (Jun 22, 2017)

What drywall will you be doing? wall? ceiling?


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## mishenka (Jan 7, 2021)

Nealtw said:


> What drywall will you be doing? wall? ceiling?


Only walls. I am leaving ceiling open and painting it black. So, only wall's drywall to the top of the framing.


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## Nealtw (Jun 22, 2017)

mishenka said:


> Only walls. I am leaving ceiling open and painting it black. So, only wall's drywall to the top of the framing.


so if you put it tight to the joist, does it cover that gap. I would caulk it after.


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## mishenka (Jan 7, 2021)

Yes, if I put drywall pretty tight to the bottom of the joist it potentially covers the gap. I suppose there is no harm if I seal, calk that gap even before drywall? What material (caulk, sealant, foam) is the best in this case? I really want to make sure it's airtight there and not going to crack over time? What about things similar to this one FOAM ?


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## Nealtw (Jun 22, 2017)

mishenka said:


> Yes, if I put drywall pretty tight to the bottom of the joist it potentially covers the gap. I suppose there is no harm if I seal, calk that gap even before drywall? What material (caulk, sealant, foam) is the best in this case? I really want to make sure it's airtight there and not going to crack over time? What about things similar to this one FOAM ?


Foam cord would be less messy
Frost King 1/2 in. x 20 ft. Grey Poly Foam Caulk Saver Moisture Repellent-C22H - The Home Depot


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## mishenka (Jan 7, 2021)

Thanks. Not to mention cheaper than foam  Most walls are pretty tight to the bottom joist, not sure if that cord will fit. But I understand the concept now.

On the exposed rim joist areas - after covering that gap with OSB or similar, do I leave the fiberglass insulation in place or replace it with rigid cutout and seal all four sides? What rigid insulation is recommended for this application if this is the way to go?


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## Nealtw (Jun 22, 2017)

mishenka said:


> Thanks. Not to mention cheaper than foam  Most walls are pretty tight to the bottom joist, not sure if that cord will fit. But I understand the concept now.
> 
> On the exposed rim joist areas - after covering that gap with OSB or similar, do I leave the fiberglass insulation in place or replace it with rigid cutout and seal all four sides? What rigid insulation is recommended for this application if this is the way to go?


When you insulate the rim you also want to think about the top of the concrete is cold too. I thin you would better to put in a good fitting rock wool, others here are saying that is approved with out anything to seal it. When I was still working the insulators were putting drywall behind any insulation up there.


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## Nealtw (Jun 22, 2017)

mishenka said:


> Thanks. Not to mention cheaper than foam  Most walls are pretty tight to the bottom joist, not sure if that cord will fit. But I understand the concept now.
> 
> On the exposed rim joist areas - after covering that gap with OSB or similar, do I leave the fiberglass insulation in place or replace it with rigid cutout and seal all four sides? What rigid insulation is recommended for this application if this is the way to go?


That cord comes in different sizes.


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## mishenka (Jan 7, 2021)

@Nealtw (or anyone who doesn't mind sharing experience) - few questions, please. Is it ok (should I) extend the OSB by half an inch beyond the edge of the framing so when I put the drywall it ends flush with the edge of the OSB? Or the OSB must end where the framing ends? I just want to ensure that the drywall (once installed) and this OSB will be tight enough together to prevent warm air reaching concrete wall - that's why I am asking.

If OSB goes where that red rectangle is - does it have to be nailed to the boards it's resting on or I only put seal with foam on three edges? Foam like this or similar?

I remember you mentioned that rookwool may be placed without anything to seal. But I don't know if you were referring to the area to seal (or not to) at the rim and sill board level where all those gaps are and I can practically see the outside in one spot, OR you meant that plastic seal that many people say goes over the insulation, like a vapor barrier? I pulled fiberglass insulation out to check for any moisture today. The paper side that was touching the rim board was not moist or wet. However it was slightly damp. The rim side was also slightly damp and cold of course. Is this level of coldness/dampness normal and expected in the winter and it will just naturally get dry later?

I really hate the idea of small gaps that clearly exist where the sill meets the joist board (horizontal) and other gaps (two sill plate abutting each other) - I literally could see the outside light! How do you feel about totally spray foaming that entire square with DAP spray foam ? Is this foam considered as vapor barrier? Will it get cold and damp the same as the vertical rim band today, meaning that I'd need to cover it with insulation anyway (mineral wool)?

sorry for so many questions - hope you can clarify all my confusions. Well.. .maybe not all, but at least related to my basement project


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## Nealtw (Jun 22, 2017)

mishenka said:


> @Nealtw (or anyone who doesn't mind sharing experience) - few questions, please. Is it ok (should I) extend the OSB by half an inch beyond the edge of the framing so when I put the drywall it ends flush with the edge of the OSB? Or the OSB must end where the framing ends? I just want to ensure that the drywall (once installed) and this OSB will be tight enough together to prevent warm air reaching concrete wall - that's why I am asking.
> 
> If OSB goes where that red rectangle is - does it have to be nailed to the boards it's resting on or I only put seal with foam on three edges? Foam like this or similar?
> 
> ...


I would leave the fire stop flush with the edge and let the drywall on the wall each the joist. 
The paper face on that fibreglass should be on the warm side any moisture you feel on it is likely from the inside of the house.


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## mishenka (Jan 7, 2021)

Got it. So, do I nail it to the boards it rests on or use a foam similar to what I showed above?


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## Nealtw (Jun 22, 2017)

mishenka said:


> Got it. So, do I nail it to the boards it rests on or use a foam similar to what I showed above?


I think I would nail it and then seal it. At least a couple nails so it can't got knocked out of place. 
You might screw up thru the top plate of the wall.


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## mishenka (Jan 7, 2021)

What about that foam that covers the entire cavity? Is it worth using it? What is the advantage of foaming the entire cavity vs. using canned foam sealant and simply apply bead of foam to the gaps that I can actually see? I mean, even if I spray the cavity to two inches deep (as they recommend) - it still leaves edge of the sill plate exposed and other gaps and crack.


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## Nealtw (Jun 22, 2017)

mishenka said:


> What about that foam that covers the entire cavity? Is it worth using it? What is the advantage of foaming the entire cavity vs. using canned foam sealant and simply apply bead of foam to the gaps that I can actually see? I mean, even if I spray the cavity to two inches deep (as they recommend) - it still leaves edge of the sill plate exposed and other gaps and crack.


If you insulate with foam it should be behind drywall if you are not doing the ceiling. 
Why not use caulk instead of foam, You can lay down a bead before you install plywood or whatever.


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## mishenka (Jan 7, 2021)

True - foam must be fire blocked by code. But I can use rookwool for that. In fact I wanted to use rockwool in those cavities anyway. 
I don't know what holds better with time - caulk or foam. That's why I am asking. But I 100% will need to use something to fix all those gaps before plywood. Just don't know which seals better and which is easier to apply. Canned foam THIS seems so easy.


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## Nealtw (Jun 22, 2017)

mishenka said:


> True - foam must be fire blocked by code. But I can use rookwool for that. In fact I wanted to use rockwool in those cavities anyway.
> I don't know what holds better with time - caulk or foam. That's why I am asking. But I 100% will need to use something to fix all those gaps before plywood. Just don't know which seals better and which is easier to apply. Canned foam THIS seems so easy.


I have never had to do that so I can't really say which is better or easiest.


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