# Rim joist insulating issue



## Chewbacka (Feb 27, 2014)

Pics would help define to us what exactly the specific problem you're encountering is. In the meantime I'll hazard a guess and say maybe your framing style is balloon style?
Seems maybe you have a subfloor added at sometime which does not connect to the original wall studs and sits proud of them, allowing air to pass into the stud bays between floors? With whatever fiberglass was installed the air carries dirt, etc. and reduces the fiberglasses ability to insulate, PLUS the air movement and fiberglass do nothing to block transfer of heat and cold to all the wrong places. Without pics I would initially say to develope a game plan to block all air flow, possibly by adding blocking at the bottom of the wall stud cavities if you can access the area with reasonable effort. Blocking should start with 2x materials sized to the space and then sealed with a canned low expansion foam. You want to block the stud bays to deter potential fire byproducts from being able to move from one floor to the next via the wall cavities: code requirement in newer houses. By adding blocking you reduce the speed at which fire/gasses of combustion, etc. can travel, which allows better chance of escape and less rapid burn rate.
The fiberglass could be left in place and you could stuff Roxul into the wall cavities, and then seal the space between the wall studs with the wood blocking and the spray foam to keep air movement to a minimum. Then use you 2" rigid foam to attach between the joists, over where the gap was before, and the open bay area where the floor meets the rim joist/sill plate. Your most cost effective rigid foam is 2" foil faced on both sides. It keeps the dew point from migrating into the living space, and keeps your conditioned, hot or cold air in summer from being lost to atmosphere.
Hope this helps; and look at some of the other recent discussions about insulating that have been posted to learn more.


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## diyGK (Oct 13, 2009)

Chewbacka said:


> Pics would help define to us what exactly the specific problem you're encountering is. In the meantime I'll hazard a guess and say maybe your framing style is balloon style?
> Seems maybe you have a subfloor added at sometime which does not connect to the original wall studs and sits proud of them, allowing air to pass into the stud bays between floors? With whatever fiberglass was installed the air carries dirt, etc. and reduces the fiberglasses ability to insulate, PLUS the air movement and fiberglass do nothing to block transfer of heat and cold to all the wrong places. Without pics I would initially say to develope a game plan to block all air flow, possibly by adding blocking at the bottom of the wall stud cavities if you can access the area with reasonable effort. Blocking should start with 2x materials sized to the space and then sealed with a canned low expansion foam. You want to block the stud bays to deter potential fire byproducts from being able to move from one floor to the next via the wall cavities: code requirement in newer houses. By adding blocking you reduce the speed at which fire/gasses of combustion, etc. can travel, which allows better chance of escape and less rapid burn rate.
> The fiberglass could be left in place and you could stuff Roxul into the wall cavities, and then seal the space between the wall studs with the wood blocking and the spray foam to keep air movement to a minimum. Then use you 2" rigid foam to attach between the joists, over where the gap was before, and the open bay area where the floor meets the rim joist/sill plate. Your most cost effective rigid foam is 2" foil faced on both sides. It keeps the dew point from migrating into the living space, and keeps your conditioned, hot or cold air in summer from being lost to atmosphere.
> Hope this helps; and look at some of the other recent discussions about insulating that have been posted to learn more.


Thanks, I'm away from home, so I had a family member take a pic. It's not the best pic but I'll try to explain. Where you see the red arrow, there is about a 2" gap between the rim joist and the subfloor- the subfloor doesn't touch the rim joist. You can see the insulation that was stuffed up there.


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## Windows on Wash (Aug 30, 2011)

Chewbacca nailed it.

The home is very likely to be balloon framed and you're going to need to incorporate another step of fire blocking that opening prior to insulating and sealing the rim joist area.


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## diyGK (Oct 13, 2009)

Thank guys. Not looking forward to the extra step. Question: if I were to, say, put drywall to close off the gap....then proceed with my rigid foam insulation up to the drywall, would this be sufficient of would I still have air leaks in that above space? I think I should rip out the existing fiberglass insulation bc everything I read states that it will trap moisture and lead to rot. 
Thoughts?


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## Windows on Wash (Aug 30, 2011)

Drywall will work but make sure it is complete and of adequate thickness.

I think you will find that wood is easier to work with.


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## Chewbacka (Feb 27, 2014)

diyGK said:


> Thank guys. Not looking forward to the extra step. Question: if I were to, say, put drywall to close off the gap....then proceed with my rigid foam insulation up to the drywall, would this be sufficient of would I still have air leaks in that above space? I think I should rip out the existing fiberglass insulation bc everything I read states that it will trap moisture and lead to rot.
> Thoughts?


It's your house. The pic is somewhat helpful but doesn't really address the wall stud cavity in so far as evaluating possible/likely existing wall damage, moisture held by the fiberglass.
How and to what extent do you plan to extract the fiberglass in the wall stud bays? Is the fiberglass merely stuffed into the bottom of the cavity and not filling the entire cavity from the cellar to the next floor?

BTW, drywall is not a moisture proof product. Cold is most prevalent at grade level at your sill plate and rim joist interface. This is NOT the place to skip a step or do the easiest quick fix. I know it's not a fun endeavor, but if you're concerned about moisture and rot this area is crucial to keeping the dew point away from your structure. The 2" rigid foil faced foam IS the way to go.
Ask any seasoned carpenter how many sill plates and rim joists/beams they've had to rip out/replace due to rot/moisture damage and or insect infestation?
Look at it this way: warm inside air wants to escape and cost you $. Cold air wants to migrate into your home and keep you feeling cold. Moisture in warm air exfiltrating to the outdoors reaches the dew point and freezes when it can escape no further, causing frost/ice in your wall structure. ALL this battle over water and air flow can be stopped by using the right materials the first time, and solve all of the above listed problems, in addition to giving you substantial and ongoing energy/$$$ savings year after year. What's not to like about the benefits of going the extra distance to gain all the benefits and peace of mind from knowing you've done the job right?!:thumbsup:


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## diyGK (Oct 13, 2009)

I took some better pics. There appears to be drywall above at the perimeter of the subfloor.
Let me know if any other pics are needed. I appreciate the help I'm getting and want to learn how to do it the right way. I am also posting a pic of the rigid foam I bought (2" r-13).
Thank you guys.


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## Chewbacka (Feb 27, 2014)

diyGK said:


> I took some better pics. There appears to be drywall above at the perimeter of the subfloor.
> Let me know if any other pics are needed. I appreciate the help I'm getting and want to learn how to do it the right way. I am also posting a pic of the rigid foam I bought (2" r-13).
> Thank you guys.


Here's what I see in the pics.
Pic 1. Cellar floor joist on left with metal BX running from that joist to one on right, not in pic. At end of joist bay sheetrock used to block between joists? Below at sill plate a black galvi pipe held by a clamp, and the white below is whitewash/ paint, stucco? on interior foundation wall. Is that a fieldstone rubble wall?

Pic 2. Having trouble identifying what's what and orientation of same. Details and angle of view please.

Pic 3. Excellent choice of insulation! Tape all seams with foil faced metal tape. Shaker can spray foam all of perimeter to joists. You could cut a 6" piece to press fit into the joist bay between the joists directly under the wall cavity, then cut a piece to fit between the joists and under the piece you just fit in place above. This would keep cold from dropping or rising in the wall cavity and keep the rim joist/cellar joist/sill plate from dew point heat transfer.

You may have to remove the existing sheetrock that is attached to the rim joist to show us what it's doing, or not to the rim joist's integrity, BEFORE doing any of the above remediation. Meaning, if there is rot behind the sheetrock and fiberglass that must be attended to BEFORE any current fixes are implemented.

Where exactly is the fiberglass that is in the old remedy?

Thanks.


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## diyGK (Oct 13, 2009)

Chewbacka said:


> Here's what I see in the pics.
> Pic 1. Cellar floor joist on left with metal BX running from that joist to one on right, not in pic. At end of joist bay sheetrock used to block between joists? Below at sill plate a black galvi pipe held by a clamp, and the white below is whitewash/ paint, stucco? on interior foundation wall. Is that a fieldstone rubble wall?
> 
> Pic 2. Having trouble identifying what's what and orientation of same. Details and angle of view please.
> ...


Pic 1- I took this pic facing the rim joist. What you see is a joist on the left. The rim joist is behind the insulation. The white you see is Sheetrock (same Sheetrock in pic 2). 

Pic 2- the left side of the pic is the subfloor. The Sheetrock you see touches he subfloor and runs up the wall. The right side of the pic is the space between the subfloor/Sheetrock and the exterior wall. The rim joist would be to the right of the insulation you see. I took the pic by pointing the camera up the gap in question. 

Pic 3- thanks. Is 2" enough or should I double it? Which way does it face?

Thanks!


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## diyGK (Oct 13, 2009)

Any thoughts guys? I'm thinking of folding over the existing fiberglass insulation to tuck it above the subfloor and then sealing everything off as intended with the rigid foam....


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## Chewbacka (Feb 27, 2014)

diyGK said:


> Pic 1- I took this pic facing the rim joist. What you see is a joist on the left. The rim joist is behind the insulation. The white you see is Sheetrock (same Sheetrock in pic 2).
> 
> Pic 2- the left side of the pic is the subfloor. The Sheetrock you see touches he subfloor and runs up the wall. The right side of the pic is the space between the subfloor/Sheetrock and the exterior wall. The rim joist would be to the right of the insulation you see. I took the pic by pointing the camera up the gap in question.
> 
> ...


Sorry, I'm still lost on pic 2? What's the yellow stuff? Is that paper backing of fiberglass?

2" is what's necessary, more can't hurt. Stuffed fiberglass is not good especially if it gets wet. Best to cut it off and seal the area with the foam-board and spray can foam. Does the Tuff-R only have foil on one side?
If so, it would be good if you could get foil facing out and in by doubling if necessary.


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## diyGK (Oct 13, 2009)

Chewbacka said:


> Sorry, I'm still lost on pic 2? What's the yellow stuff? Is that paper backing of fiberglass?
> 
> 2" is what's necessary, more can't hurt. Stuffed fiberglass is not good especially if it gets wet. Best to cut it off and seal the area with the foam-board and spray can foam. Does the Tuff-R only have foil on one side?
> If so, it would be good if you could get foil facing out and in by doubling if necessary.


Yes the yellow on the right is the paper backing of the fiberglass. I took this shot looking "up" into the gap we've been discussing. The Sheetrock you see is the very same Sheetrock you see in pic 1 (you can see the bottom edge of it). The Sheetrock runs up into the celing/floor above. 

I'm confused as to how to treat the area above the gap. I'm referring to the space above the subfloor. It is sheetrocked and there is space between the Sheetrock and exterior wall (pic 2) where there is fiberglass insulation that runs down into the rim joist area. My idea is to take the fiberglass insulation that runs into the rim joist and fold it up into the gap so that above area is doubled, and then seal off the rim joist with the rigid foam and spray foam as initially intended.

The Tuff-R has foil on one side. If it's important to have it on both sides, I can buy thinner/cheaper pieces and add a layer.


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## Chewbacka (Feb 27, 2014)

Most all of the Tuff-R I have used has a silver colored foil on both sides of the 2" board.
I would cut the fiberglass out in the area you plan to seal because of what I already mentioned re water/moisture retention. Then jam the foam board in snugly to keep air movement in the wall cavity to a minimum. Seal the perimeter with cans of spray foam and you're done.
The foam board doesn't know or care about how it's oriented, but I'd try to get foil facing toward the cold, and if double sided foil it will also face the conditioned space.
Whatever you do to stop drafts, dewpoint, migration and water from entering your home will be good for it and for you. Check after winter, or during and see if there are any changes of 'climate' in the area you sealed; meaning any frost or cold air in the area, evidence of water running down the interior wall of the cellar. There should be none of those issues, but if you encounter any post back what's going on.
Meantime, show use pics of the install step by step in case we need to modify the plan. Or in case we need a laugh!? Just kidding, of course.:yes:

And, I'd check Dow's website about the different types of Tuff-R and best use of the various foil backed products and their recommended application methods for different situations.
Here:http://building.dow.com/en-us/produ...c_itemid=cc6d2205-eb58-414d-a404-ed7b743e385e


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## diyGK (Oct 13, 2009)

Chewbacka said:


> Most all of the Tuff-R I have used has a silver colored foil on both sides of the 2" board.
> I would cut the fiberglass out in the area you plan to seal because of what I already mentioned re water/moisture retention. Then jam the foam board in snugly to keep air movement in the wall cavity to a minimum. Seal the perimeter with cans of spray foam and you're done.
> The foam board doesn't know or care about how it's oriented, but I'd try to get foil facing toward the cold, and if double sided foil it will also face the conditioned space.
> Whatever you do to stop drafts, dewpoint, migration and water from entering your home will be good for it and for you. Check after winter, or during and see if there are any changes of 'climate' in the area you sealed; meaning any frost or cold air in the area, evidence of water running down the interior wall of the cellar. There should be none of those issues, but if you encounter any post back what's going on.
> ...


I'm about to start, but want to make sure we are on the same page, so I took 1 more pic and labeled it as best I can. I'm not sure what to do above the subfloor bc the fiberglass insulation runs up there and I don't know how far up it goes. For all I know it runs up the wall into the above floor. Should I just leave it and cut off the portion below the subfloor, put 4" of rigid foam and use spray foam to seal it up?


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## diyGK (Oct 13, 2009)

I found a good pic. Please see RED and GREEN comments I added. This should further clarify my situation. 

To make things more complicated, there's a vertical stud running in each section. Is it okay to have a 2" gap between the rim joist and rigid foam if I choose to go right over the stud, which will keep the foam fro touching the rim joist?'
this can be seen on my 2nd pic, illustrated by the green arrow.


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## Chewbacka (Feb 27, 2014)

Yes. Cut the fiberglass so it's not folded, stuff the cavity with foam board, seal with spray foam and keep doing the same until the area is done.


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## Chewbacka (Feb 27, 2014)

Seeing the pics, I missed them somehow last night, just put the rigid foam board from where the green arrow points at the cellar floor joist across the cavity, covering the fiberglass AND stud, to the next floor joist and snug to the subfloor. Then spray foam the perimeter, DONE. On to next bay. Cut or don't the bunched up fiberglass at the bottom so it's less bunched and duct tape it to the wood just below where you make the cut, or not. Once the area is sealed the fiberglass is largely irrelevant.
Now go do it!:thumbup:


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## diyGK (Oct 13, 2009)

Chewbacka said:


> Seeing the pics, I missed them somehow last night, just put the rigid foam board from where the green arrow points at the cellar floor joist across the cavity, covering the fiberglass AND stud, to the next floor joist and snug to the subfloor. Then spray foam the perimeter, DONE. On to next bay. Cut or don't the bunched up fiberglass at the bottom so it's less bunched and duct tape it to the wood just below where you make the cut, or not. Once the area is sealed the fiberglass is largely irrelevant.
> Now go do it!:thumbup:


I completely understand. My concern is still moisture/rot, however. The area will be sealed from basement air (interior), but outside air can still come into the cavity from the exterior. Won't this air be able to cause issues since it will be trapped in between the rim joist and the space I'm creating by putting the rigid foam over the vertical wood stud (The fiberglass batt lives inside this space)? This air can travel up the wall as well. I guess I can lift the batts out of the way spray from the perimeter to block air leaks first.
Thoughts?
Thanks


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## Chewbacka (Feb 27, 2014)

I can only see what you show me, but if it were my house I'd probably, as I said originally, cut out the already damaged by water, section of fiberglass/paper, and fit some rigid foam board in alongside the vertical stud and against the rim joist, then seal below that as I just described.
Unless you go outside in the spring/summer months and peel back the siding and whatever else is there and inspect everything and then upgrade to more recent methods/materials, you'll continue to have moisture issues, etc. This current method is a stop gap, literally, so you're not heating the outdoors. It won't fix what's wrong with the house, but it's a good beginning.:drink:


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