# Rim Joist insulation



## sile16 (May 1, 2012)

I've been adding foam board with Great stuff in the rim joists. But, I've got some overhangs where some A/C vents go into and there isn't enough room to properly install the XPS with great stuff around it. What is the best way to insulate around the A/C vents?

In this case, the joists go about 2' past the foundation.


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## joecaption (Nov 30, 2011)

Just stick some fiber glass insulation in the best you can. It's Got to better then it was when your done.


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## Windows on Wash (Aug 30, 2011)

Roxul or Fiberglass.

Roxul is more air impermeable than fiberglass and a bit easier to cut into shapes.


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## Fix'n it (Mar 12, 2012)

what is on the other side of the foundation ?


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## Gary in WA (Mar 11, 2009)

See if that register boot will push upward after removing the nails in the sub-floor to install the f.b. Just tin snip off the extra or buy a close-bend boot. Ideally. for optimum value would be adding f.b below the joist bottoms and replacing the soffit wood outside. This would prevent "radiation" and provide a thermal break from the ground/outside air temp. and the joist which is R-1.25 per inch.....http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Gary


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## Trucon01 (Jan 10, 2012)

When insulating the rim joist do you:

1. Cut foam to fit rim and spray foam around it

OR

2. Caulk rim, insert foam and then spray foam?


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## Gary in WA (Mar 11, 2009)

#2 to air seal the rim as it expands/contracts with the seasons; pp.51, http://books.google.com/books?id=iw...age&q=heel or toe bearing with rafter&f=false

http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

http://www.conservationtechnology.com/building_design.html#AirLeakagePathways

Gary


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## Trucon01 (Jan 10, 2012)

Thanks Gary. You've been a huge help with all of my projects so far...


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## Trucon01 (Jan 10, 2012)

Here is my progression with the rim joists.

I also have a basement project where you can see the whole project...

http://www.diychatroom.com/f49/2012-basement-demo-130727/index3/


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## hammerlane (Oct 6, 2011)

spray foam works good also


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## Trucon01 (Jan 10, 2012)

Indeed. How much did that run you for just your rim joists?


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## hammerlane (Oct 6, 2011)

Trucon01 said:


> Indeed. How much did that run you for just your rim joists?


$800 for 166 lineal feet of rim joists and a 200 sq foot of wall space in an attic area above a garage.

Attached are a few photos:

The top 3 are of the attic area above the garage. The last is my basement setup.

After they did the spray foam in the attic area I fluffed up all existing batt insulation and laid new batts across the joists.


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## M3 Pete (May 10, 2011)

You have a chandelier in the attic? Very classy.


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## hammerlane (Oct 6, 2011)

M3 Pete said:


> You have a chandelier in the attic? Very classy.


 
Yeah right. Took it out of the dining room when we moved in and put in a ceiling fan. Been trying to sell it but no takers yet. Figured its safer in attic than down in basement.

Actually the 1st photo below shows when I still had batt insulation in the rim joist cavities.


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## Gary in WA (Mar 11, 2009)

Looks good! I was surprised while researching that 1/16" air gap will admit moisture to the rim joist. Just caulk the joints/small holes the SPF missed. 

If the attic is not used for storage or attics not joined, an ignition barrier only is required over the SPF for fire-safety;http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec016_par007.htm

if used for storage; a thermal barrier is required per Code: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec016_par003.htm 
Some foams are acceptable, ask your local Building Department.

Is there soffit venting, as I don't see the air chutes there?

Gary


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## hammerlane (Oct 6, 2011)

GBR in WA said:


> Is there soffit venting, as I don't see the air chutes there?
> 
> Gary


You can see the air chutes better in this before photo. WIth the new pink insulation you cant see the chutes from the angle I took the photo but the chutes are definitely not blocked.


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## Windows on Wash (Aug 30, 2011)

Looks good.

Not sure why they wouldn't use blown in but that is my only question/concern with it.

They insulation schedule looks fine but blown in cellulose is so much easier and better.


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## Gary in WA (Mar 11, 2009)

Chutes are there! You are almost done.....

Have you seen a hot-air balloon rise on the thermals, then sink back down when the air temperature rises past early morning? There are convective loops in your (all) attic when temperature differences exist. The sun heats the roof deck/house to start the loops. If you blocked the holes from wiring/plumbing from the basement/crawl which help cause the "stack effect", you will be ahead of the game.http://www.wag-aic.org/1999/WAG_99_baker.pdf

Some of the remaining attic heat will be removed by the intake/exhaust venting, but you still have convective looping above your f.g. insulation--- *Fig. 7"h"*; http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1059&context=mechengfacpub&sei-redir=1&referer=http%3A%2F%2Fwww.google.com%2Furl%3Fsa%3Dt%26rct%3Dj%26q%3Dvelocity%2520of%2520rising%2560%2520attic%2520air%2520from%2520passive%2520ventilation%26source%3Dweb%26cd%3D39%26ved%3D0CGkQFjAIOB4%26url%3Dhttp%253A%252F%252Fdigitalcommons.unl.edu%252Fcgi%252Fviewcontent.cgi%253Farticle%253D1059%2526context%253Dmechengfacpub%26ei%3DqKtiT5ClBMXe0QHf6eDFCA%26usg%3DAFQjCNEttRcYqHsDOwb6ZhW2A5Hx8ncVIA#search=%22velocity%20rising%60%20attic%20air%20from%20passive%20ventilation%22

Read "Conclusions", pp.9 and 10 above--- you will always have convective loops over your batts which are------ air-permeable (goes through it like a sieve). http://findarticles.com/p/articles/mi_m0KWZ/is_3_6/ai_n8582994/
You do have the heat from below countering the wind-washing... somewhat. Also *if *you used high-density batts rather than low-density; http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/

My point: cover the batts with a housewrap like Tyvek for an air-barrier *or* 3" of cellulose insulation (blanket); to prevent cool air from degrading it's R-value.

Gary


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## Windows on Wash (Aug 30, 2011)

+1 Gary. :thumbsup:

Another reason that fiberglass is a PITA in my world. Blown in cellulose is a 1 stop deal.


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## ANDYK. (Jul 29, 2012)

my basement rim joists are insulated like the pic from hammerlane- unfaced fiberglass stuffed in. Is this bad? The house is 32 years old. Of what I've pulled out, I don't see any moisture issues. It looks like you guys like to use the foam panels and foam/caulk to seal out moisture. This would take me forever with the hvac vents and electrical running thru. I would just like to replace the unfaced fiberglass to make it look nicer...and add more. Some original areas are half full...just stuffed in/or one small piece...looks messy. Lots of cobwebs, etc. I want to use the pink to make it look new and clean(yeah, im nuts). I'm worried about moisture after reading some posts. Also, if I fill up the whole cavity(maybe 2 ft. deep), is there any issue of over-insulating? I did a few with unfaced r-30 and was able to put in about 3 pieces. It looks nice and clean.....I just dont want to cause any damage. I'd appreciate any advice. Thanks.


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