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Insulating over concrete garage floor

Paula Mueller | Posted in General Questions on

Our home is older – built in 1923, and has a great garage space, with a concrete floor that slopes outward. Several years ago, I repurposed the garage into a home gym, adding rolled covering that is 2.5mm thick. However, I still didn’t like the slope of the floor as it limited the way I can arrange equipment. So, a couple of years ago I built a raised floor using high grade cedar decking – 6″ x 1″ on 12″ centered floor joists. The floor is beautiful, stable, and works perfectly. Now I would like to insulate the space between the rubber matting and the raised floor. Can I use rolled fiberglass insulation in that space? There are no leaks in the garage.

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  1. GBA Editor
    Martin Holladay | | #1

    If in your experience the garage floor stays dry, I suppose that you can install fiberglass batts between your floor joists. They won't do as good a job as a continuous layer of rigid foam, of course, because of thermal bridging through the joists, but they'll help with heat loss a bit.

    Another way to improve the thermal performance of this floor is to install vertical rigid foam on the exterior side of the perimeter of the slab. This type of insulation would need to be protected with metal flashing. The top of the flashing would need to be integrated with your wall's water-resistant barrier (WRB) or with your siding.

  2. Paula Mueller | | #2

    Thank you, Martin. I'll give these options further consideration. If I use the rigid foam, I would need to pull up more boards to install. But, if it does a better job, perhaps it's worth it. Thanks again.

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