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Old 02-25-2010, 12:26 PM   #1
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Rim Joist Insulation


Great info on the same kind of project i'm currently doing. I do have a few questions that the Interwebs can't seem to answer to my satisfaction:

  1. Does it matter whether I use caulk or canned foam to seal the gaps after I've inserted the precision-cut piece of rigid foam? Currently I'm using Todol Pur Fill 1G Foam with a Todol foam gun, but at $17/can, it's starting to add up.
  2. So after i've caulked/foamed the rigid foam in place, do i have to then continue by cutting out pieces of drywall to cover all of the foam? If yes, what's the best/longest lasting caulk I should use to seal it with? Should it be the fire-rated caulk? If I chose not to cover the rigid foam, would that fail a home inspection?
Thanks for any information you may provide,

HeloOne

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Old 02-25-2010, 10:01 PM   #2
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Rim Joist Insulation


This is a tricky question. Foam is better since it will last longer and fill better. Caulking will work. You do not have to cover with drywall. The joists act as a thermal bridging. Now is some areas code may still require it. The code did allow it not to be used then it required it and now it is again being removed. So latest codes will not require foam to be fire protected at the rim joists.

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Old 02-26-2010, 07:04 AM   #3
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Thanks for answering my questions, Bob! It'll save me a lot of time not having to cut drywall

Next stop: attic air leaks

Thanks,
HeloOne
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Old 02-26-2010, 09:50 AM   #4
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attic air leaks are done the same way. look for wall openings, recessed lights, plumbing and electrical penetrations. Caulk all ceiling covers for lights and vents.
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Old 02-26-2010, 10:04 PM   #5
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Be aware canned foam is not for non-insulated (older) can lights (require 1/2" clearance to insulation box), masonry chimneys (required metal fire-stopping then insulation on top, or gas flue exhaust pipes (and wood-burning metal pipe, require thimble or insulation shield). There is certain fire-rated foams, caulking and hardening liquids for this.

Be safe, Gary
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Old 02-26-2010, 10:17 PM   #6
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Not before i gained incredible knowledge from sites like this, I had my electrician install non-ic recessed lights in my family room. At the time, I didn't fully understand that cutting six holes in my ceiling would at to the existing air leak problems I have. Now, I know about icat recessed lights or the building of boxes out of rigid foam or drywall to cover non-ic lights to block air loss.

Has anyone ever build the boxes out of the rigid foam to cover non-ic lights? Seems like a lot of work but less $$ than replacing lights. I just had mine installed November '09. Since I'll be up in my attic this spring sealing all the gaps and cracks with foam, it's something i'm seriously considering.

Thanks for your replies.

HeloOne
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Old 02-27-2010, 09:17 AM   #7
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some have but it is not safe or legal. use drywall and tape and caulking. The metal duct tape will hold up the cloth will not last. And drywall boxes are cheaper and easier to make than foam anyway. Seal the bottom and seams with spray foam.
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Old 02-27-2010, 10:20 AM   #8
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Thanks, Bob, for the reply.

Since i won't be using duct tape to hold these drywall boxes together, what kind of tape is recommended to keep them sturdy and square?

-HeloOne

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