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Installation of mineral wool insulation in shop

LucyF | Posted in Energy Efficiency and Durability on

First question ever asked here. We’re building a shop in Upstate SC, mixed humid climate. We are insulating it for comfort so it can easily be used year round. We chose mineral wool insulation for its fireproof properties. The studs are 2 x 6 so they are using 3″ mineral wool and 2″ mineral batts. They have used a minimally expanding foam around all the studs, electrical outlets, any penetrations. That looks good. I am concerned about the compression as they stuff the mineral wood in. I’ve got a few pictures I will try to attach.

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  1. LucyF | | #1

    These are my photos. The builder will be closing in the wall soon so I'd like to make sure it's good before we do that.

    I realize it's Christmas though I actually have to go to work for a few hours. Ya'll have a very Merry Christmas. I hope everyone is home and healthy and happy and warm.

    Thank you for all your helpful information through the years.

  2. albertrooks | | #2


    With low density batts, compression will reduce their effectiveness. try and get the MW batts uncompressed and leave no voids for air. If you can seal the drywall to the framing, that will help reduce thermal looping. Each stud bay should be uncompressed and entirely filled with MW, and then sealed on all 4 planes.

    A warm shop.... I'm jealous.

  3. davidmeiland | | #3

    How can they get completely full by combining 3" and 2"? There's going to be an airpspace in there. The photos show what I think is a typical low-quality batt install.

  4. LucyF | | #4

    I picked out the worst looking areas, most of it is not compressed quite that bad. Do you think I can kind of fluff it up, uncompress it so to speak? I think the guys are working tomorrow. I will get my brother (it's his shop) to talk to them about the compression. He usually leaves the insulation issues to me because I read so much about it, but I have to work all night.

    I knew it was not ideal, but I didn't think it was that bad.

    We're using the shop as practice for my brother's house which is next year's project. I am educating the contractor and his crew about air sealing, insulation, gaps, embodied energy, etc. but stuff still happens. You guys know how it goes better than I do.

    I won't let them close up the walls until we get this right.

    Thank you.

  5. adam5532 | | #5

    Roxul makes R23 5.5" thick mineral wool batts that are perfectly sized for 2x6 stud bays (in 15.25 and 23 inch widths), so I'm not sure why your contractor is using 3" plus 2", which is insufficient. As said before, there should be no air space (where convection currents of air could circulate and loose heat), and the drywall should be air-sealed to the studs with flexible caulk or acoustic sealant. The Roxul Comfortbatts are great -- I just used them for a project because they are fireproof (vastly superior to foam in this respect), fit tighter than fiberglass, and don't hold water. They are fragile, so they require some care in unpacking and placing so that pieces don't break off.

  6. LucyF | | #6

    Adam, I wanted to use Roxul. I've actually used it in an attic and I think it is better than this form of mineral wool. It seems to hold it's shape better. I did not know that it was available in 5.5" which would have been perfect.

    The insulation company we're working with routinely orders from a different supplier. He said that the Roxul was too hard to get. I special ordered mine for another project from Home Depot (can you say that here?)

    I LOVE to insulate(I actually think it is fun), but I work in the health care field and wintertime is prime time for us so I was not able to do the insulation.

    The shop we are building is a precursor to my brother's house. So I view this building experience as practice for the real thing.

    What I really need to do is to talk to the guy in charge of the insulation, rather than just my contractor. I have avoided that because I did not want to get into an argument about insulation. He thinks I am crazy because I won't use fiberglass. I should have gone over specifics about batt insulation to my standards (not his crew's standards) before the installation.

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