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Insulation fill code


guy48065's Avatar
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04-27-16, 08:52 AM   #1  
Insulation fill code

A carpenter buddy was helping me with a project and he mentioned that it's code that the insulation in stud cavities must completely fill the space and be in direct contact with the back of the sheetrock. He says the reason isn't for insulation efficacy--it's for the fire stop. This surprised me and seems hard to be 100% in compliance, not to mention yet another inspection point. Is it true?

 
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Bud9051's Avatar
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04-27-16, 09:01 AM   #2  
I'm not an expert on codes, but from what I know, the insulation itself does not meet the fire stop requirements, thus we need a 2x4 or other member every 8' or so. I think your buddy was just passing on hearsay with his own emphasis added.

I do energy audits and use an infrared camera and although I can see hot and cold spots I would be hard pressed to say absolutely that there was a void. Could simply be a hole in the sheathing.

Bud

 
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04-27-16, 09:36 AM   #3  
If you are using the insulation as a firestop, then yes, the cavity has to be completely filled if you are using mineral wool insulation, and even tightly compressed if fiberglass. So this would be at transition points between walls and ceiling spaces and other places where a fire stop is required.

Here's a decent reference on fire stopping basement walls: How to Firestop Your Basement | Contractor Kurt

If the insulation in question is just for thermal insulation, like in stud bay, it is a good idea to fill the space from an insulation efficiency standpoint. In the thermal case, you don't want the insulation compressed, but you don't want big air spaces either.


Paul

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04-27-16, 05:11 PM   #4  
We have no idea what construction method was used (balloon construction?)
What type insulation your taking about.
No form of insulation is a fire stop.

 
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04-27-16, 05:34 PM   #5  
Joe, both mineral wool and Fiberglass insulation installed tightly compressed are approved fire stop materials.


Paul

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04-27-16, 06:15 PM   #6  
CT, although your link and some searching do indicate the tightly packed fiber insulation is listed in the codes as approved I would want to pass it by my local code authority as it is a sketchy area and might not be accepted. The sketchy part is the often quoted advice of not compressing fiberglass insulation and now we are being told to do so, but not how much. A 2x something across the cavity eliminates any questions.

Solid wood also has the advantage of blocking critters who love to explore through wall cavities that are not blocked. I have seem many trails with the IR camera, not only do they lessen the insulation performance, but they find a place to make a potty and it is disgusting.

I concede it meets the codes as shown, but when has minimum code been the best solution?

Bud

 
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04-27-16, 06:27 PM   #7  
I don't use it across the top of stud cavities, but mineral wool is handy for stuffing duct and pipe penetrations and for providing a thermal barrier in front of spray foam on the rim joist in areas where the ceiling won't be finished. I personally don't use Fiber for this for the reasons you state. I wasn't recommending it, just stating that it is an approved option.


Paul

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04-28-16, 08:59 AM   #8  
OK so it's acceptable to use insulation as a fire stop but it must not be common since there's disagreement on the application of it. At least that's my "between the lines" take on it...

BTW in my present case it was just a toss-off comment since I was insulating an interior wall for sound deadening.

 
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04-28-16, 11:28 AM   #9  
Because of that same disagreement this question becomes a good one for local code officials, they always have the last say.

Bud

 
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