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Wall insulation choices on remodel

user-7147194 | Posted in General Questions on

Hello GBAr’s

My name is Chris climate zone on margins of 5/6, doing an extensive remodel.

Thanks to those that helped with my attic insulation question.

Having that settled, we are moving on to the walls.

The walls are 2×6, osb, tar paper, air gap, then brick veneer

My contractor has offered me three choices

1) net and blow fiberglass

2) 2” closed cell then blow In fiberglass 

3) fill entire cavity with open cell foam, although he was concerned about condensation issues with this one…by my understanding, I’m not sure that is a valid concern.

Which of these is the best option?, or is there a better alternative?

 Just FYI, dense or damp pack cellulose or dense pack fiberglass are not things the building community around here are very familiar with, but if these are better options I could try and press someone to do it. 

Thanks for any advice or opinions.

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  1. Expert Member
    Dana Dorsett | | #1

    Net-blown fiberglass is usually done at 1.8lbs density, which is a dense-pack density for that material.

    An all open cell solution is fine without interior vapor retarders in zone 5 when there is an air gap between the sheathing and cladding, but may need a "smart" vapor retarder such as 2-mil nylon (Certainteed MemBrain) or half-perm "vapor barrier latex" primer. Either one works, 2-mil nylon becomes more vapor open than v.b. latex if the moisture levels reach mold-worthy levels.

    Closed cell foam between studs is a waste, offering little more than vapor retardency, despite the higher R/inch. It's also the least green option- a full fill of open cell uses less polymer, and is blown with H2O (water) instead of HFC245fa, which is soon to be banned for this application under the Kigali amendment to the Montreal Protocol due to it's extremely high global warming potential. The higher R is severely undercut by the thermal bridging of the studs, gaining less than R0.5 in "whole wall R". Save the high R/inch foam budget for continuous layers that cover over the stud edges, not between R1.2/inch studs.

    R23 rock wool batts designed for 2x6 framing will outperform any of the above if fitted correctly. The sheathing needs to be detailed as an air barrier prior to installation (as is the case for blown fiberglass too.)

  2. user-7147194 | | #2

    Thank You Dana,

    The purpose of the foam is to make an air barrier....I’m guessing that the level of detail necessary to make an effective air barrier on this retrofit is not likely to be had amongst the insulation folks in this area.

    I’m not sure how that would be done, with tapes?

    If I didn’t mind driving myself insane, I guess I could try and do a cut and cobble approach?

    The ceilings on floor one and two (3 story house) have also been removed and the rim joist exposed, and the thought was the foam could also seal this notoriously leaky assembly.

    I also neglected to mention that is will be finished with Sheetrock and paint. So if I went with opencell foam, would you put the smart vapor barrier just deep to the Sheetrock ?

    Love the rock wool idea, but again, requires meticulous attention and I’m just skeptical I can find someone with that level of dedication (especially having dismantled the previous insulation wadded around electrical outlets with adjacent big black streaks in the batts from the infiltration)

    Thanks again for your insights

  3. Expert Member
    Dana Dorsett | | #3

    A case of polyurethane caulk and a powered caulking gun make quick work of sealing of sealing the full perimeter of each stud bay to the OSB, and the bottom plate to the subfloor, the seams between any doubled up top plates/jack studs/etc.

    Tape can be used on any horizontal seams. Can foam should be used to seal any electrical & plumbing penetrations of the framing (including horizontal penetrations of studs, not just top & bottom plates.) Trimming batts to fit around electrical boxes isn't rocket science, neither is splitting batts to accomodate wiring rather than wadding it up behind the wire. With reasonably air tight cavities and a reasonably snug fit batts really can do it, using no more equipment than a batt knife- no blowers or sprayers required.

  4. punkdr | | #4

    Thanks Dana,

    I met again with the insulation contractor, and got the pricing options. Yes, cc sprayfoam is quite expensive!

    I am favoring a hybrid approach at this point and was wondering what your thoughts would be.

    I want to use 1"ccsf on the rim joists as this is the most complex area to caulk, and then use caulk and tape in the stud bays below.

    Then I have options to fill with. I did talk to the insulation contractor about dense pack cellulose again and they said if that is what i wanted they would do that, but they were really trying to talk me out of that option. Is dense pack cellulose a sensible option ?

    Their preferred option is to blow in fiberglass.

    Should I try for mineral wool batts, after they spray the rim joist and I caulk/tape the bays?
    The insulation contractor hasn't mentioned that as an option, but i could ask about it if that would be the sweet spot for performance/price.

    Thank you again


  5. Expert Member
    BILL WICHERS | | #5

    Rockwool/mineral wool is a good product. I think it’s more conducive to installing with a proper fit too since it holds it shape and can be cut around things. Fiberglass batts are often just stuffed around things like electrical boxes. Mineral wool batts have to be cut to fit, so you’re more likely to get a tight fit as long as some minimal care is taken with the cutting. Mineral wool tends to be less forgiving in that it doesn’t spring back after being stuffed in and fill little voids in careless installs the way that fiberglass can.

    I’d try for mineral wool or cellulose. I hate fiberglass, too many itchy days spent working in the stuff.

    I think 1” is a little thin for a rim joist in your climate zone. I’d go for at least 2”. You can add mineral wool batts for more insulation value on top of that if you want.


  6. user-723121 | | #6

    I have found the DAP Dynaflex 230 to be a good latex sealant choice for air sealing of studs, rim joists and the like. It has a lot of body and does not seem to shrink or dry out like some of the lesser latex caulks. Rim joist areas can be made quite airtight with a bit of effort including caulk, fiber and rigid insulation, production builders in the Twin Cities use spray polyurethane in the rim joist area for new homes.

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