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Seansmom 01-06-2013 08:55 AM

Great stuff on top of fibreglass batt?
I have been working on insulating rim joists. So far I have pulled out all old pink batts, caulked joints, installed 2" XPS and caulked that in place. We want R20 so my next step is another layer of 2" XPS cut a bit narrower glued in place then great stuff around the foam and over the sill plate right to the top edge of the finished wall. That works good for everywhere except on the end where the joist runs parallel to the side of the house. The joist sits out about 4" from the wall and in the cavity is a duct pipe, the fibreglass in there was stuffed so tight up around the back and top of the pipe that I couldn't get it out. (I may be able to dig it out with a wire hanger.) I was thinking of just leaving it and putting a few layers of great stuff to completely seal it inside and then fill the whole cavity with great stuff. Once I trim the great stuff i can drywall flush to the joist.
Being a newbie I figured I would run this by you guys first to make sure I am not setting myself up for future issues.

Fix'n it 01-06-2013 10:09 AM

can you post a pic ?

Seansmom 01-06-2013 11:59 AM

3 Attachment(s)
Hi, I have attached pictures. I put the insulation back while waiting to decide what to do. If I do succeed in pulling it all out with a coat hanger I am concerned that I won't be able to get the great stuff up on top and in the back corners....
Pic 1 is the corner of the house where the duct goes up to through the floor.
Pic 2 is face on what it looks like.
Pic 3 you need to rotate and it is looking straight up to the floor above.

Fix'n it 01-06-2013 12:17 PM

i don't see why you can not do what you plan. though i don't see that completely air sealing that area = the duct could get very cold. is there any way to get to the rim joist from the outside ?

Seansmom 01-06-2013 02:05 PM

I don't think i can get at it from outside and right now we have about 3 feet of snow so I can't check. That's one of my fears. If I seal it that way then the pipe is on the outside of the air seal so I am worried about that pipe getting cold. It goes to the 2 nd floor master bedroom (my bedroom). Maybe I'll try to dig out the old fibreglass and use the big gap filler. Still not sure how to handle this one.

Seansmom 01-06-2013 03:12 PM

It's been like that for 40 years. Maybe I'll just add more batt and then close the gap with a panel. But make it removable so I can take it down and check it for moisture a couple of time a year. Laser thermometer shows no cold spots and it is pretty cold outside today.

Fix'n it 01-06-2013 08:49 PM

i think that is what i would do. but i would use roxul. and i would check the outside to see if there is a way to air seal from there.

i have bricks on the inside of my rim joists. i could air seal over them, but i don't like that idea. and removing the bricks is a PITA, i did a few bays, not fun.
so i am going to air seal on the outside when i do the siding.

Seansmom 01-07-2013 06:31 AM

I think Roxul would be easier to work with. I hear it is less itchy. It will depend on what is sold in small packages because I don't need much.
Thanks for the advice.

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