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Old 01-24-2009, 05:59 PM   #1
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insulating crawl space near plate


I want to insulate my crawl space near the outer walls to reduce heat loss through the space above the sill plate. I have read that putting fiberglass insulation bats the full height of the floor joists from the band joist to about 2 feet into the crawl will adequately insulate the area.

Should I use insulation with a vapor barrier?
If so, should the vapor barrier be towards the sub-floor?

What is a good way to support the bats so they don't slip out over time?
(another thread mentions a mesh for this purpose. Does anyone have a product name?)

My sill and foundation are dry. But would I be increasing the risk of rot because I could be hiding leaks or collecting moisture?


At this point I am not looking for perfection but our floors are cold near the outside walls and our main heating service duct runs through the crawl.

Thank you in advance, even if all you do is read my post.

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Old 01-25-2009, 05:52 PM   #2
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insulating crawl space near plate


Have you thought about just using a rigid (foamboard) style insulation and seal with a PL or Acoustic seal even?. Looks nicer and won't have to worry about it getting wet or dirty or falling out

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Old 01-25-2009, 06:57 PM   #3
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insulating crawl space near plate


I used Roxul insulation for this! It is fire rated and has reduced moisture absorbency! Not as expensive as foam. Here's their web page! http://www.roxul.com/sw34086.asp
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Old 01-25-2009, 07:52 PM   #4
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While your down there , you could get a few cans of the small gap spray foam and hit the foundation and sill gaps all along the top of the foundation.you will be surprised on the drafts that come from this area.
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Old 01-26-2009, 12:01 AM   #5
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sealing the gaps there and adding insulation is one of the best ways to help keep in the heat good luck
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Old 01-26-2009, 08:12 AM   #6
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insulating crawl space near plate


Using fiberglass around the rim joist is a no no. It will allow moisture to build up through condensation and rot your rim joist and sill plates out. Foam is the only product for this application. Fortunately you can purchase rim joist DIY foam kits just for this application. The only alternative is cutting foam to size and then sealing all 4 sides after installation with a can of spray foam. Don't use the fiberglass unless you have first installed 2 inches of foam to act as a vapor barrier. This is a big no no and rots out many a sill and rim joist in colder climates.

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Old 01-26-2009, 09:55 AM   #7
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those 2 part do it yourself spray foam kits are about 625 bucks on e-pay.(plus another 100 or so in shipping costs) Was watching "this old house" on PBS this weekend and the guy said a kit like that costs about 350 bucks. Where does one find them for that??
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Old 01-26-2009, 12:50 PM   #8
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I have my doubts about fibreglass insulation rotting the rim joist! Here in Canada, there at least 10,000,000 homes with this method. I have never seen or heard of this being a problem! Although. it must have a vapor barrier installed on the warm side!
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Old 01-26-2009, 01:22 PM   #9
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Quote:
Originally Posted by 4just1don View Post
those 2 part do it yourself spray foam kits are about 625 bucks on e-pay.(plus another 100 or so in shipping costs) Was watching "this old house" on PBS this weekend and the guy said a kit like that costs about 350 bucks. Where does one find them for that??
Don'T know about the kits you mentioned but would like to know more about them, I was thinking along the lines of the 5.00 a can spray foam from HD. What episode was that ? BOB
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Old 01-26-2009, 01:34 PM   #10
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Quote:
Originally Posted by Wildie View Post
I have my doubts about fibreglass insulation rotting the rim joist! Here in Canada, there at least 10,000,000 homes with this method. I have never seen or heard of this being a problem! Although. it must have a vapor barrier installed on the warm side!
Wildie I have seen this happen in a basement, in up state new york. where these people had a summer home with a full basement, insulated floor bays with the vapor barrier facing up. water seeped into the basement from the windows ( snow melting ) no heat down there everything was shut down for the season. well during the summer they invited me and my family up there, not knowing what they had in mind . ( installing a sliding door) . opened up the wall and noticed the floor was springy. under the oak flooring. we went into the basement and i discovered the entire floor structure was covered with black mold. from the fiberglass down only. took my hammer and smack the beam and it disintegrated. went to yank on the electric wires and the beams split. the entire floor structure was shot.
I doubt very much this could happen in this posters case because of the heat ducks helping to keep things dry, but there could be a possibility. I don't know for sure. BOB.
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Old 01-26-2009, 02:26 PM   #11
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I have seen many sills and rim joists rotted out because of fiberglass installs against the rim joist. It was not allowed under inspection where I previously worked. Too large of a mass of framing leads to heat loss which in turn allows for condensation. Most builders started installing 2 inches of foam on the outside and offsetting the rim joist to solve this problem.

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Old 01-26-2009, 03:01 PM   #12
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I've seen a case where the rim joist rotted and fibreglass insulation was used in the joist bay. However, water had penetrated from outside and was held there by the insulation. However, this wasn't because of the insulation, it was because water was able to penetrate form outside! In this case, any kind of insulation would have trapped the moisture.
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Old 01-26-2009, 03:02 PM   #13
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Is this the same as the band joist? If so, according to the owens corning website, your should insulate it with unfaced batts of insulation

"The band joist should be caulked and sealed to prevent air infiltration at the construction joints and around all penetrations such as plumbing, electrical lines, and heat/AC and dryer vents."

"For the band joist, use unfaced cut-to-fit pieces of insulation and place them snugly into the space. "
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Old 01-26-2009, 03:11 PM   #14
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Originally Posted by daveyd View Post
Is this the same as the band joist? If so, according to the owens corning website, your should insulate it with unfaced batts of insulation

"The band joist should be caulked and sealed to prevent air infiltration at the construction joints and around all penetrations such as plumbing, electrical lines, and heat/AC and dryer vents."

"For the band joist, use unfaced cut-to-fit pieces of insulation and place them snugly into the space. "
No mention of a vapour barrier? Its my understanding that water vapor will travel through fibreglass and that a vapor barrier is to be installed on the warm side to prevent this!

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