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Spider v. ProPink L77 blown-in fiberglass v. cellulose for wall retrofit as well as attic spaces. STC comparisons?

Kevin Green | Posted in Energy Efficiency and Durability on

I have been scouring the Forum for info to compare options of Cellulose, Fiberglas, etc., for retrofit applications. 

The ‘Getting to Know Spider Insulation’ from 2013 was very helpful and gave me the confidence that this would work well in my application.

The contractor now advises he cannot get that product locally anymore (PDX, OR), so is using ProPink L77 – apparently both for drill/fill in wall and as loose fill in crown/flat attic spaces.

Does anyone have experience with the product?  
How does the STC of this compare with Cellulose and Spider?
It reads that it is “dry” blown – so apparently does not have any binder or sticky additive like Spider.  Is it therefore at risk of settling?  Perhaps not because it is fiberglas and would be dense packed to a 1.8 – 2.2 lb/cuft range?

The project is retrofit insulation of 1938 cape/bungalow style house.
Goal is insulation but equally important is noise reduction from exterior as we live on a busy street.
Climate Zone 4C.
No moisture issues have been observed, nor issues with peeling exterior paint.
Noting that basement insulation has been completed:  spray foam rim joist, 2 x 1.5″ XPS on walls, seams taped, bottom caulked, foam sill gasket for framing.

I will outline entire project and plans(*) in case I have missed something in my reading.  

– Cedar shake siding exterior
– smooth shake 2nd course
– shiplap sheathing
– 2×4   (*retrofit with blown-in insulation)
– lathe/plaster interior

Knee Attics:
– Improperly installed insulation removed
– BX wiring replaced with NM-B
– *Rigid/spray foam blocking for cathedral spaces, spray in same dense-pack insulation from above.
– *Air sealing with caulk/foam/putty on all penetrations
– *Plan is Rockwool batts, VPAB, 2nd course of UltraTouch denim for additional sound isolation, attached with twine in perpendicular direction.
– *Blow-in dense pack of same in floor cavities after blocking towards habitable space with rigid foam/spray.  (Happy that this will help with air sealing the leaky rim)
– *Blow-in on top of attic floors to reach R-38 in total.
– *Contractor adding single vent per space where not present

Crown Attic:
– BX wiring replaced with NM-B
– *Air sealing same as for Knee, also for light fixtures, adding a few IC-rated can lights
– *Blow-in dense pack to cathedral spaces (blocked below as noted)
– *Blow-in loose fill same insulation to R-38

THANKS to everyone on the Forums for sharing your expertise over the years, it is seriously helpful, thought-provoking and educational.

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  1. Expert Member
    Rick Evans | | #1

    Hi Kevin,

    L77 is a good fiberglass product. It's not dusty or itchy and it compacts well. I doubt you will have to worry about settling. Because fiberglass is hydrophobic, it will not hold moisture and settle on its own weight if the density isn't quite right.

    My home has 12" of L77 within double stud walls. It's wicked quiet. But I wouldn't rely upon insulation to be much of a sound barrier. Air spaces, etc do a better job of that. There has been much written about this topic on GBA if you search. Also, check out the STC ratings for various wall assemblies at the Underwriter Lab website. It is an excellent resource.

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