# Best insulation for irregular spaced studs?



## bcemail (Sep 18, 2010)

I've got an exterior wall that's been built and DIY'ed by previous owners so there's a range of spacing on the studs. It's anywhere from a few inches next to a window or door to 24" OC and I've got it down to the studs. Main wall is about 25" long by 8' (plus a couple inches) tall. Two side walls are 12' long but the insulation there is mostly intact. There is also Romex running around the room for the outlets and lights.

It seems 24" insulation is less available at the big box stores and some I'm finding is unfaced. I was planning on using faced batts with no vapor barrier since I'm in zone 7. With batts, I know I'd be doing a lot of cutting for width plus to go around the Romex, outlets, and light switches. I was thinking about using foam board. Maybe 2" and 1" or double 1.5", one layer behind the Romex and then another on top with gaps for the Romex. Maybe spray foam around the edges to seal everything. Does this make sense? I know the foam board might be more per foot per R value but might be easier to install.

Other option is spray foam. Hiring would be more expensive. I'm looking into DIY spray foam but not sure if I would save much money.

Thanks!


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## chandler48 (Jun 5, 2017)

24" R13 insulation is available, and may be your best bet. I'd use faced insulation with the vapor barrier to the inside.









Knauf Insulation R-13 EcoBatt Kraft Faced Fiberglass Insulation Batt 3-1/2 in. x 23 in. x 93 in. 506576 - The Home Depot


Knauf R-13 EcoBatt Kraft faced fiberglass insulation with ECOSE Technology is a leading sustainable insulation. All of our batts are bonded with the revolutionary, industry-transforming, plant-based ECOSE



www.homedepot.com





XPS has a lesser R value and is much more expensive. Spray foam is excellent, but way out there in price. Spray foam is not so much a DIY thing, unless you have access to the equipment chemicals and tools.


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## Nealtw (Jun 22, 2017)

Most house get cut to fit insulation, regular insulation you cut to fit. Cut 1/2 to 1" to big so it stays in place.


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## bcemail (Sep 18, 2010)

chandler48 said:


> 24" R13 insulation is available, and may be your best bet. I'd use faced insulation with the vapor barrier to the inside.
> 
> 
> 
> ...


Thanks, I was reading that as just being 93" total but it looks like there's 11 in the pack! I'll just get a couple of those and cut to size. Thanks!


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## bcemail (Sep 18, 2010)

Nealtw said:


> Most house get cut to fit insulation, regular insulation you cut to fit. Cut 1/2 to 1" to big so it stays in place.


Makes sense, I wasn't sure with the paper that has the tabs if it was OK to cut smaller, but I guess I can just pull some paper off the edge to staple? Thanks


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## Nealtw (Jun 22, 2017)

bcemail said:


> Makes sense, I wasn't sure with the paper that has the tabs if it was OK to cut smaller, but I guess I can just pull some paper off the edge to staple? Thanks


I guess so, I have not seen paper backed here for 40 years. The one place that always causes trouble are outlets and switches where you have less insulation, the paper cut back and air leaks around the box


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## chandler48 (Jun 5, 2017)

You only have 93" in the stud bay, so they are cut for full installation.


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## gthomas785 (Mar 22, 2021)

With irregular spaced studs you are going to have to cut some insulation one way or another, just ask yourself if you'd rather be cutting fiberglass or foam board. Don't bother with the paper backing, it is a joke. Fill the bays and then sheet over the whole wall with plastic and tape the seams. It's easier and a more effective vapor barrier.


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## bcemail (Sep 18, 2010)

Nealtw said:


> I guess so, I have not seen paper backed here for 40 years. The one place that always causes trouble are outlets and switches where you have less insulation, the paper cut back and air leaks around the box


Oh, I thought paper backed was standard but sounds like it's not? If not I'll go with plain insulation and then vapor barrier


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## bcemail (Sep 18, 2010)

gthomas785 said:


> With irregular spaced studs you are going to have to cut some insulation one way or another, just ask yourself if you'd rather be cutting fiberglass or foam board. Don't bother with the paper backing, it is a joke. Fill the bays and then sheet over the whole wall with plastic and tape the seams. It's easier and a more effective vapor barrier.


Good to know, I thought paper was typical since I see it in my house (although it was probably installed 40 years ago). I guess fiberglass is pretty quick and easy to cut? I used some foam board for another project and ripped everything on my table saw, but I'll also be left with lots of pieces I can't use. I'm guessing FG is also a lot cheaper and then I can just plastic the whole thing. Do I just cut around the outlet boxes and tape as best I can around them? Thanks!


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## gthomas785 (Mar 22, 2021)

The kraft paper facing is typical and commonly used. Depending on where you live it may be adequate, but I find a full plastic VB works better and and is hardly any more work or expense.


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## jim_bee (Feb 23, 2021)

Depending on your climate zone, you may not need a Class I vapor barrier (e.g., poly) and it may be detrimental in some areas. 

Check out this article from the Insulation Institute.


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## Randy Bush (Dec 9, 2020)

Personally with a lot of odd spacing I like having blowing insulation dense pack done. Think it does a better job of getting every where.


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## bcemail (Sep 18, 2010)

jim_bee said:


> Depending on your climate zone, you may not need a Class I vapor barrier (e.g., poly) and it may be detrimental in some areas.
> 
> Check out this article from the Insulation Institute.


Thanks! I'm in Zone 4 and the code I found reads:
"Class I and II vapor retarders shall not be provided on the interior side of frame walls in Zones 1 and 2. Class I vapor retarders shall not be provided on the interior side of frame walls in Zones 3 and 4. Class I or II vapor retarders shall be provided on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4."

So I guess no Class I, but I can choose if I do Class II or not? Sort of confusing how it's worded.


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## bcemail (Sep 18, 2010)

Randy Bush said:


> Personally with a lot of odd spacing I like having blowing insulation dense pack done. Think it does a better job of getting every where.


Thanks, just started looking into that as well. Any opinions on BIBS (which I guess is fiberglass) vs. cellulose blown in? Would prefer to do either myself.


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## SW Dweller (Jan 6, 2021)

Saw a guy on Utube that cut sheets of insulation a bit short and put them in the bays of his wall.
He used a can of spray foam to make the sheet solid and fit tight. 
I thought it was a good idea for the situation.

Foam can be a lot better than fiberglass. However we are all aware of the expense.
I did my garage door with solid sheets, set up my table saw and it was the best way for me to get straight cuts


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## bcemail (Sep 18, 2010)

SW Dweller said:


> Saw a guy on Utube that cut sheets of insulation a bit short and put them in the bays of his wall.
> He used a can of spray foam to make the sheet solid and fit tight.
> I thought it was a good idea for the situation.
> 
> ...


Thanks, last year I had to seal up our soffits which were leaking air into the ceiling space. Did the same thing with 2" XPS foam and spray foam. Ripped everything on the table saw then foamed into place. Expense doesn't look like it would be too much more, as long as it's something that can be there for decades I'm fine with it. So much information about R-values, moisture permeability, temperature ranges, etc., that my head is swimming with insulation lately!


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## jim_bee (Feb 23, 2021)

bcemail said:


> So I guess no Class I, but I can choose if I do Class II or not? Sort of confusing how it's worded.


That's the way it's interpreted here. Note that this language is new to the building code and may not have been incorporated yet where you are. So you might want to check with the building official to make sure you don't create an issue with that office.

The kraft paper backing on fiberglass insulation is class II and latex paint is class III.


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## turbo4 (Jan 30, 2021)

Its doesnt get any better than foamboard cut a little small then can foam the gap to make it airtight. Doesnt shrink or settle.Ive seen fibrglass put in so poorly its was little more service than an air filter. Plus its hard to get a good tight fit around wires. I have a lot of 4 inch foam i cut to fit.


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## Nealtw (Jun 22, 2017)

Installing insulation in irregular cavities - YouTube

EP 12 : VAPOR BARRIER INSTALLATION - DON'T MAKE THESE MISTAKES! - YouTube


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