# Rim Joist Insulation Best Option



## joecaption

Remove the fiberglass and replace it with 2" thick foam and seal the gaps with expanding foam.
The outside air will just blow right through those batts.
If your finishing the basement why insulate the ceiling?


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## Windows on Wash

Winner winner chicken dinner.


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## Fix'n it

Windows on Wash said:


> Winner winner chicken dinner.


your making me hungry


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## hammerlane

I vote spray foam. I had fiberglass batting but went the spray foam route. Completely stopped drafts and also find less bugs in basement.


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## hammerlane

Still vote for spray foam


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## Gary in WA

SPF can be $$$. And, as you said; " I’m thinking spray foam would be better but cost is a factor as always" Second best is XPS/canned foam for a 13% air leakage reduction (whole house) for a $125 yearly savings, pp.6, 7, 12; 
http://www.google.com/url?sa=t&rct=...sg=AFQjCNEwnyx8any5u8iy0hzz-E2r-HlzSA&cad=rja

"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. These considerations are reflected in the recommendations of section F." From; http://www.buildingfoundation.umn.edu/RimJoist/rimjoistphenom.htm

Gary
PS. Welcome to the forums!


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## North_Woods

Well I went to my local box store this afternoon and found that I can buy a SPF kit and apply it myself. I didn't know they solds these kits before today. Looks pretty straight forward. I'm no professional builder but am pretty handy around the house. Does anybody have any expreience applying SPF themself with one of these kits?

Hammerlane - Did you do that yourself? Looks great by the way. How far from the end wall of the joist caviety should be filled in with foam, to the interior face of the vertical wall below? In other words how deep did you go? Did it just stick to your OSB sheeting in your actic? That's pretty cool.

joecaptain - Insullation in the joist cavieties for noise reduction, not so much for insulation. I was given a bunch of 12" thick R30 non-faced rolls and figured these would be perfect. I know they make actual sound proofing foam and sheeting products, but I figured the R30 batt would work well for my needs. Is there any reason I shouldn't install it?

Gary - Thanks for the very detailed info! And thank you for the welcome.


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## msaeger

joecaption said:


> Remove the fiberglass and replace it with 2" thick foam and seal the gaps with expanding foam.
> The outside air will just blow right through those batts.
> If your finishing the basement why insulate the ceiling?


Could you leave the fiberglass in there and put the foam in front of it?


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## North_Woods

msaeger - you mean leave the fiberglass against the outside wall and spray the foam on the inside of that? I certainly could do that. What would the benefit be?

Anybody spray their own foam with one of the kits?


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## mikegp

He means rigid foam in front of the fg batts. From the basement floor to the subfloor is my guess.


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## mikegp

So putting fiberglass in the rim joist behind the fb.


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## hammerlane

North_Woods said:


> Hammerlane - Did you do that yourself? Looks great by the way. How far from the end wall of the joist caviety should be filled in with foam, to the interior face of the vertical wall below? In other words how deep did you go? Did it just stick to your OSB sheeting in your actic? That's pretty cool.


I had a local company do it. Got a good deal because he had a cancellation and I was able to have him do it with one days notice.

The majority of my rim joists were about 6" deep and 9" in height. I had a few deeper one under two bay windows .Yes he filled all the way to the rim joist. And yes it just stuck to the OSB.


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## mikegp

Hammerlane, does that gap under your sill plate in the last pic make it all the way to the outside? Did you caulk it or anything? Or is it just a gap until it hits the plate?


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## hammerlane

mikegp said:


> Hammerlane, does that gap under your sill plate in the last pic make it all the way to the outside? Did you caulk it or anything? Or is it just a gap until it hits the plate?


That little deflection in the sill plate seal did not allow go thru to the outside. I did not caulk it. But I noticed on about 4 feet of the sill plate around one of my rear facing basement windows, the builder forgot to put the sill plate seal. I did caulk there.

Here is what ideally should be done 360 degrees.


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## North_Woods

Thanks guys.

mikegp - that makes more sense with the rigid foam. Thanks for the clarification.

Hammer - thanks. I'll have to call and see if I can get a quote compared to doing it myself. I'm surprised nobody has done the SPF foam application themselves. Looks pretty easy, just maybe messy. My joist ends are deeper than 6" and my joist height is 12". Either way it looks like I should cut and fit rigid foam or go the SPF route. It was 22 below zero this morning and I tried to detect a draft by the batting that's there now and really couldn't do it by touch alone so I think it's pretty tight to start.

Thanks!


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## hammerlane

North_Woods said:


> . It was 22 below zero this morning and I tried to detect a draft by the batting that's there now and really couldn't do it by touch alone so I think it's pretty tight to start.
> 
> Thanks!


When you remove the batt insulation and look at the face that was against the rim joist, do you see dirt or discoloration on the batt insulation? This would indicate air movement


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## Gary in WA

Hammer, why are there still wall forms against the wood wall with slab concrete already poured, why was plate an inch short of wall end and overhanging wall on front, why the cold-joint in the concrete wall pour, why are the J-bolts short of getting the proper length of thread above the nut- lot of extra work chiseling the plate down. Does the concrete wall sit *on *the concrete slab? Instead of abutting it (per minimum code) with a (IMO) thermal break (FB) between them? I hope I'm wrong, here.....

Gary


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## hammerlane

Gary in WA said:


> Hammer, why are there still wall forms against the wood wall with slab concrete already poured, why was plate an inch short of wall end and overhanging wall on front, why the cold-joint in the concrete wall pour, why are the J-bolts short of getting the proper length of thread above the nut. Does the concrete wall sit *on *the concrete slab? Instead of abutting it (per minimum code) with a (IMO) thermal break (FB) between them? I hope I'm wrong, here.....


Cant answer any of those "Why" questions you ask. If you happen to find this home or the person who built it then maybe you can get those answers. I was just showing the sill plate seal from a google search for sill plate seal.


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## msaeger

North_Woods said:


> msaeger - you mean leave the fiberglass against the outside wall and spray the foam on the inside of that? I certainly could do that. What would the benefit be?
> 
> Anybody spray their own foam with one of the kits?


I was asking if it's ok to do that.


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## North_Woods

hammerlane said:


> When you remove the batt insulation and look at the face that was against the rim joist, do you see dirt or discoloration on the batt insulation? This would indicate air movement


 There is a little but not much. I've decided to look into the spray foam as far as getting a quote just to see what it would cost. If it's too much I'll look into doing it myself with one of the SPF kits or will do the rigid foam with sealer.

As far as adding friction fit 12" thick unfaced R30 between the joists throughout the ceiling for more noise reduction than anything else... is this a good idea or not? I know they make sound proofing foam boards and other products but they are all way more expensive than just fiberglass. I'm sure they work better too but adding the fiberglass should help right? I can get a bunch of R30 from a buddy pretty cheap so the price is right too.

hammerlane - did you ever put anything between your joists or leave them open?


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## hammerlane

North_Woods said:


> hammerlane - did you ever put anything between your joists or leave them open?


What do you mean did I ever put anything between the joists? The way you see with the spray foam in post #5 is the way it is now.


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## mikegp

I think he means insulating between the joists.


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## North_Woods

Yes, I meant in the rest of the ceiling other than the rim area or did you spray foam the entire joist gap from end to end? Sorry for the confusion.


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## hammerlane

North_Woods said:


> Yes, I meant in the rest of the ceiling other than the rim area or did you spray foam the entire joist gap from end to end? Sorry for the confusion.


I think when you say ceiling you mean the underside of the subfloor??

The average cavity was 14.5" from joist to joist, 9" high and 6" deep. Yes the spray foam touched the underside of the subfloor shown by yellow in the photo.


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## North_Woods

Maybe a photo will help. The rest of the open gap area between the joists directly beneath the subfloor, the area that you did not apply the spray foam to. This is the area some folks add insulation or sound proofing materials to. I was just wondering if unfaced 12" think R30 batt would be a good product to add here for reducing noise?


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## hammerlane

No I did not add anything there but I believe It would help keep floor above warm and aid in sound


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## North_Woods

Thanks Hammer.

Has anybody else added anything to this between the joists area for sound proofing?

Thanks!


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## Dave Sal

North_Woods said:


> Maybe a photo will help. The rest of the open gap area between the joists directly beneath the subfloor, the area that you did not apply the spray foam to. This is the area some folks add insulation or sound proofing materials to. I was just wondering if unfaced 12" think R30 batt would be a good product to add here for reducing noise?


Roxul has a product for sound deadening called Safe and Sound. I think it would be better than Fiberglas for sound absorption as it is more dense.

http://www.roxul.com/products/residential/roxul+safe'n'sound


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## Gary in WA

Roxul (52 STC) or FG (50 STC) are neck-n-neck for sound, Best to decouple the drywall from the ceiling framing with channels. Both get wet/loss of R-value, both are air-permeable, though rock wool is better in a fire. http://www.roxul.com/files/RX-NA_EN/pdf/SafenSound.pdf

Compare *#10;*http://www.certainteed.com/resources/Guide%20for%20Residential%20Sound%20Control.pdf *Also, #12, 13* for sound at floor....

http://www.google.com/url?sa=t&sour...sg=AFQjCNEN_j-wXM2AA2UNU07zZTmsW6TAjQ&cad=rja

http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/90-controlling-heat.html

Leaving the air gap to the floor sheeting will also benefit warmth as well as sound; http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance

Gary


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## Windows on Wash

Dave Sal said:


> Roxul has a product for sound deadening called Safe and Sound. I think it would be better than Fiberglas for sound absorption as it is more dense.
> 
> http://www.roxul.com/products/residential/roxul+safe'n'sound


As Gary said, they seem to be neck in neck but I absolutely prefer Roxul over FG.

:thumbsup:


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## Gary in WA

IMHO; I agree, if asking for opinions only. 

Gary


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