GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Frostproofing an existing slab on grade

jeff hibbard | Posted in GBA Pro Help on

I am a residential designer working out of northern Wisconsin. I have a project I am working on that has an existing house with a full basement built about 10′-0″ from an existing slab-on-grade garage. I would like to attach the garage to the house with a breezway-type addition. Is there a way to frostproof the existing garage either by digging down 4′-0″ vertically & sliding rigid insulation into the trench, or I believe I have seen shallow frostproofing where rigid insulation is laid horizontally just below grade out to a point out 4′-0″ from the edge of the slab. Or a combination of both? If anybody has any solutions, or input I would greatly appreciate it.
Thank you,
Jeff Hibbard

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jeff,
    If the garage is unheated, I don't believe that it's possible to frost-proof the slab by adding foam at the perimeter. Think of it this way: when it's -20°F outdoors for three days in a row, it's going to be -15°F inside your garage. The slab will freeze, and so will the soil under the slab. Normally, assuming the slab is placed on a deep layer of crushed stone, such a "floating slab" can work fine for a residential garage. But once you try to tie it to a house on an independent foundation with footings below frost level, differential movement can lead to problems.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |