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Installing R-60 insulation over 1/2″ nailed drywall

Matthew Haraminac | Posted in General Questions on

I’m wanting to insulate my attic to ~R-60 but upon further evaluation, the current R-10 blown-in mineral wool already exceeds the weight recommendations listed in the USG Gypsum Construction Handbook of 1.3 pounds per square foot. My first thought was to use an insulation support fabric such as Insulguard, though I’ve personally only seen those products used for retaining insulation in wall cavities. The technical bulletin for Insulguard Heavy Duty states it can support 55 psi which is well beyond the weight of cellulose installed to R-60. Is this an appropriate use for that product?

I’ve also considered placing OSB sheathing, EPS foam, Celotex, or possibly even a layer of drywall on top of the truss chords to support the additional weight, but I thought I’d check here to see if anyone has any other/better suggestions. The last thing I want to do is cause the ceiling to sag or encourage nail pops.

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Replies

  1. Jennifer M | | #1

    Can you install mineral wool batts across the beams, instead of within them and directly on top of the blown-in material? This places the weight on the beams and is a good air-sealing strategy, too.

    1. Matthew Haraminac | | #2

      Thanks so much for the insight. I was wondering about that but kind of wrote off the idea. If it would work that would be preferable because I wouldn't be adding any material that wouldn't contribute to R-value. Do you suppose the even distribution of insulation above the batt combined with the inherent rigidity of Rockwool would prevent them from sagging into the cavity over time? I would assume yes, though I don't want to be a guinea pig. I wonder if there are any documented instances of this assembly?

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