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Community and Q&A

Exposed Rockwool in unfinished basement shop and mechanical room

TylerKC | Posted in Energy Efficiency and Durability on

House location: Kansas City
Exterior cladding: 1/4” fiberboard over 1” EPS (covers rim joist and part of foundation)
Room in question: 32’x18’ unfinished room in basement serving as the mechanical room/workshop….3 walls are cement foundation, 4th wall shared with finished basement space.

Question: I recently removed faced fiberglass insulation from the rim joists and replaced with 2” pink XPS (against joist), foam can sealed around the XPS perimeter, then covered the XPS with R-15 Rockwool. I was happy with my work until reading about the health concerns of exposed Rockwool, especially considering it’s location in my situation:  mechanical (HVAC) room and where I like to putz around with projects. 

Should I cover the Rockwool with a smart vapor retarder to eliminate the health concerns? Shoot, could I even take down the Rockwool, shove the pieces in plastic bags, and re-install?

Appreciate your responses! It’s my first GBA post! 

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  1. Expert Member
    BILL WICHERS | | #1

    What health concerns are you worried about? Rockwool is generally considered to be a pretty safe product, usually safer than fiberglass. I doubt you have anything to worry about here.

    If you’re concern is vapor/condensation, the XPS should protect you here. 2” of XPS should be enough to prevent condensation issues at the interface between the XPS and Rockwool unless maybe you’re in a REALLY far north climate zone. Once you have enough rigid foam to keep condensation at bay, you can add some Rockwool to add a little more R value without concern. You basically want to keep within the same ratio of rigid foam to fluffy stuff that is given for walls using exterior rigid foam.


    1. TylerKC | | #2

      Hi, Bill. The health concerns are breathing in any airborne particles caused by air movement within the space. Perhaps the risk is minimal. Regardless, if I elect to safeguard to ease any paranoia/concern, I’m interested to understand options that don’t introduce moisture concerns or other risks.

      1. Expert Member
        BILL WICHERS | | #3

        The only dust issues are usually during installation of the material. Once you’re done with the installation, there should be no future issues with dust. It’s usually recommended wear a dust mask while working with the material.

        If you’re still concerned (I don’t think you need to be), you can replace the mineral wool with additional rigid foam.


  2. Expert Member
    Akos | | #4

    You can spray a bit of paint over it to seal it up. Painting the joists and bottom of the subfloor at the same time makes a big difference in the amount of light in the place. Messy job but definitely worth it for a workshop.

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