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seeking advice on insulating rim joists
Posted by: mattkime
Date: September 12, 2021 09:44AM
This is obviously related to my mouse removal thread below.

---

I'm removing the insulation around my rim joists because its fiberglass which makes for great mouse bedding. Also, it really doesn't do much insulation wise in absence of an air seal. Out it goes.

But what to replace it with?

There are options, and strong opinions out there, but I'm having trouble choosing. I've decided that going with spray insulation is out due to the work involved removing or covering any and all objects in my basement. Its a fast way to seal and insulate IF nothing is in the way. Its also kind of expensive. This leaves board insulation. Styrofoam like products.

XPS looks like a good option except that it doesn't meet fire code. Thermax looks like a good option but it doesn't perform as well in cold temps and thats exactly what I need out of it. Sometimes mineral wool is recommended which is fire rated but I get the impression that its an oddball choice. Fiberglass or a similar material may be applied as a second layer.

Oh, I'm aiming for R values between 15 and 20.

For a project which largely involves cutting squares and inserting them into voids, picking the material is surprisingly complex. Maybe I need to find the right forum.

Anyways, advice appreciated

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Edit: Seems that thermax works fine at low temps because only the outer inch is affected and losing an r value point doesn't mean much. Now to research its reduction of R value over time.







Edited 2 time(s). Last edit at 09/12/2021 10:10AM by mattkime.
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Re: seeking advice on insulating rim joists
Posted by: mikebw
Date: September 12, 2021 10:43AM
My opinion is that you should cut and layer up rigid foam to whatever R value you want, then seal around the edges with spray foam.
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Re: seeking advice on insulating rim joists
Posted by: modelamac
Date: September 12, 2021 12:45PM
Quote
mikebw
My opinion is that you should cut and layer up rigid foam to whatever R value you want, then seal around the edges with spray foam.

smiley-score010



Ed (modelamac)

I think I will just put an OUT OF ORDER
sticker on my head and call it a day.
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Re: seeking advice on insulating rim joists
Posted by: davester
Date: September 12, 2021 01:07PM
Your best bet is probably mineral wool/rock wool rigid panels. Fireproof, no global warming agent gases, decent R-value per inch.



"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion." (1987) -- Carl Sagan
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Re: seeking advice on insulating rim joists
Posted by: mattkime
Date: September 12, 2021 01:32PM
I think the solution is to use thermax but rate it at 5 instead of 7



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Re: seeking advice on insulating rim joists
Posted by: Thrift Store Scott
Date: September 12, 2021 02:47PM
You might find this interesting-

Testing The Burn Ability Of Insulation In Wall [www.youtube.com]

Depending on cost and availability, maybe put a layer of stainless steel wool (won't rust) against the rim joist to help prevent mouse intrusion and then insulate behind that?



WARNING- If I posted a link in the above message, assume it is at minimum "NSFW- Language". Occasionally you'll be wrong.

Lie to me if you must, but don't lie to me and insult my intelligence in the same sentence.

Resist the Thought Police: George Orwell's book 1984 was meant as a warning, not an instruction manual.

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Re: seeking advice on insulating rim joists
Posted by: mikebw
Date: September 12, 2021 07:44PM
Quote
Thrift Store Scott
You might find this interesting-

Testing The Burn Ability Of Insulation In Wall [www.youtube.com]

Depending on cost and availability, maybe put a layer of stainless steel wool (won't rust) against the rim joist to help prevent mouse intrusion and then insulate behind that?

Neat. I imagine if the wall had been closed on both sides however that the results would not have been so interesting to watch.
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Re: seeking advice on insulating rim joists
Posted by: mattkime
Date: September 12, 2021 09:48PM
Quote
Thrift Store Scott
Testing The Burn Ability Of Insulation In Wall [www.youtube.com]

Its definitely interesting but annoying that he didn't specify the kind of foam board he used.

I'm not sure if thermax is sold anymore, but there is similar 'polyiso' board. Seems its necessary to read the data sheet to determine the fire rating. This has a fire rating of <25 - [www.menards.com]

While home depot's offering is only <75 - [www.homedepot.com]

Lower is better. 0 is cement board and 100 is red oak. XPS isn't fire rated because it melts.







Edited 1 time(s). Last edit at 09/12/2021 09:48PM by mattkime.
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Re: seeking advice on insulating rim joists
Posted by: anonymouse1
Date: September 12, 2021 11:42PM
If you're willing to pay $ to have someone do it for you, there is a kind of concrete blow-in foam that should solver all your problems. Have to a find a contractor, though....
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Re: seeking advice on insulating rim joists
Posted by: davester
Date: September 13, 2021 05:50PM
Quote
anonymouse1
If you're willing to pay $ to have someone do it for you, there is a kind of concrete blow-in foam that should solver all your problems. Have to a find a contractor, though....

That's called AirKrete. I had it blown into our walls. It's not suitable for the application that mattkime is asking about though.



"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion." (1987) -- Carl Sagan
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