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Interior Walls-Mineral Wool: R-value marked or Sound Attenuation Fire Blanket?

PatriciaCranberry | Posted in Green Products and Materials on

Is there a difference? I was looking at Rockwool R-15 ComfortBatt or Owens Corning Thermafiber R-15 UltraBatt….but then I notice the non-R-“rated” mineral wool called Thermafiber SAFB (2.5 pcf).  Looks like essentially the same product, right? 

My questions:
Since its for interior walls and primarily for reducing sound transmission, will it matter which I choose? Won’t the SAFB still have R-Value qualities even if it isn’t “listed” as such? And does it even matter? Is there a difference in the R-value density versus the SAFB density I see listed on the spec sheet? Any other brands/products that would perform the same function for interior walls at lower costs?

This is wood framed. 2×6 exterior 16″ O.C. studs with 1″ XPS CI on exterior. Planning on R-23 mineral wool batts on those exterior walls but want interior walls addressed as well. This structure will have multiple mini-split units providing heating/cooling needs.  I’m getting ready to get quotes on different types of insultion. I’ll be doing the install myself and love the ease of the friction fit. Thanks in advance. 

Central Oklahoma. CZ3

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  1. Expert Member
    BILL WICHERS | | #1

    The primary difference between the R-rated insulation and the sound absorbing variant is the thickness. The sound absorbing stuff is intended to leave an air gap inside the wall, so that it’s only in direct contact with one side of the wall. This helps to reduce sound transmission more than if the insulation completely filled the stud cavity.

    The Owens Corning sound insulation has a note that if you need an R value rating from them for the product you can ask and they’ll send you something. I imagine Rockwool has a similar note, but I’ve never checked. Either product has thermal insulating value, with the thinner sound absorbing variant having less total R value due to the reduced thickness, but the same R value per inch.

    I would just use the R value rated stuff in exterior walls where it matters and you want maximum R value and a full fill of insulation in the walls, and use the thinner sound absorbing variant in any interior walls you want to have better sound reduction properties. There isn’t a huge difference in sound reduction ability between the two thicknesses, so you’ll still get good sound reduction in your exterior walls this way.


  2. Expert Member
    Akos | | #2

    When it comes to sound the type of insulation doesn't matter much, all of them do about the same job.

    There are levels of quietness, you have to figure out how far you want to go. For basic interior sound reduction, batts in the walls and 5/8" drywall installed in "air tight" manner is decent.

    If you want quieter than that, go with resilient channel on one side. Home theater room, 2 layers of 5/8 over resilient on both walls and ceiling.

    For exterior walls, it really depends on what is near you. With a busy street, I would go with at lest 5/8" drywall over resilient channel. For more attenuation, a staggered 2x4 double stud wall on 2x6 plates is better but pain to insulate.

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