Insulating rim joist


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Old 05-20-18, 02:20 PM
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Insulating rim joist

Hello! I decided to finish my Unfinished Basement. On the of the first tasks I decided to do was to insulate all around the Rim Joists. Unfortunately, I encountered a dilemma because on the south side the space between the Floor and Rim Joist is minimal:
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As you can see, the vertical space between the wall and joist is only 1.5in (there is no horizontal space) that only a baby's hand would fit.
What I have been doing to insulate so far on the other sides is putting a 1in Foamular 150 Rigid Foam, sealing it with expanding foam around it, and then a layer of Roxul Comfortbatt R15 cut to fit which would also make it fire proof.
I saw Sealing / insulating between joist and sill plate but for me, that joist is NOT facing the garage. It would be the outside.
I was thinking about stuffing Roxul/Rockwool as much as I could, but I also read not to compress it otherwise it would lose its insulation value.
Does any one have any ideas how to proceed and insulate that side?

Thanks!
Andres
 
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Old 05-20-18, 05:24 PM
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There are a couple of ways but they both require using an instant rise two-part foam insulation kit. These kits are fairly expensive and also have a definite learning curve.

The first method would entail drilling holes every 12 to 18 inches in that engineered joist and then injecting the foam while moving the gun all around. With practice you should be able to squirt in enough foam to completely fill the space without the expanding foam putting undue stress upon the engineered joist.

The other method, maybe a bit better, would be to adapt a piece of vinyl tubing to the nozzle of the foam gun and shove it in between the engineered joist and the rim joist. You need to work fast as the foam begins to set up in less than 20 seconds.

Down sides, the cost of the foam may be so high that the payback time is many years. Also, if the expanding foam from the top of the space is impeded by already hardening foam from below it could actually force the engineered joist out of position. Making sure you get enough foam in to fully fill the space without overfilling is the secret.
 
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Old 05-21-18, 01:47 AM
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I've used the Froth insulation kits and they are a PITA in the best of circumstances not to mention the overall cost.

So how wide is the cavity, about the thickness of the wall?

You have to work with what you have, I'd just use a couple layers of thin R15 insulation compressed through the gap.
 
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Old 05-21-18, 06:14 AM
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Thanks for the input Furd, I definetely looked into that, but as you mentioned, the price is what drove me away. I definitely want to do a good job on the finish, but it would certainly break the bank.
Something that I was just thinking is to seal the bottom part with rigid foam and some expanding foam creating dead air space (sealing the holes of cables running through too). Then, between the first and second floor joist use the batt that I was originally going to use creating the R value.
From what I have been reading, it is better to have dead-air space rather than be in contact with the cold wall. It might not be as effective as the rest of the insulation, but still cost effective.
Of course, my only concern is that there won't be the same fire retardant protection on that side as the others.
 
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Old 05-21-18, 06:21 AM
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So how wide is the cavity, about the thickness of the wall?
The cavity is about 6-8in and if it is anything like the other sides, there is going to be a bunch of nails sticking out that can block me from properly shoving the batts up.
 
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Old 05-21-18, 01:35 PM
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I had something similar where a sunroom addition butted up to an irregular stone wall,
I found that tubes of 2" circular foam water pipe insulation worked nicely,
It compressed into the small space between the outer rafter and irregular wall, and stayed sealed against the walls.
The trick was to use a yard stick to push it into place, if it was pushed in too far you use a loop of ribbon to pull it back into place, and just slide along as the foam tube is pushed into place.
 
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Old 05-21-18, 03:42 PM
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From what I have been reading, it is better to have dead-air space rather than be in contact with the cold wall.

I would not, not insulate, that cavity extends beyond the wall meaning when it gets cold you will have cold air contacting the floor on the inside of the insulated wall, a very cold. uncomfortable, and inefficient thermal break.

Stuff it with something is far better than nothing!
 
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Old 05-22-18, 08:20 AM
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Thanks! I will fill the space with batts and just leave the rigid foam out. I would have loved to used the instant rise foam, but maybe another time.
 
 

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