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Retrofitting an old stemwall to be frost protected?

Bdgray's picture

We live just outside of Chicago. In the backyard behind our master bedroom was formerly a 20'x20' concrete patio with a brick wall surrounding it. The thing was at least 20-30 years old and showing its age so I tore it out last summer. When I did I discovered a stem wall that spans the perimeter of the old patio. I assume it was installed to support the weight of the brick wall above it. Now I'm hoping this stem wall is a gift. My wife and I have been considering an addition to our MBR for years. The dimensions of this stem wall fit exactly where we have planned the addition.

Here is the problem. The stem wall isn't to code. It is wide enough (12") but it is only 36" deep. I believe code in this part of Illinois requires 42" below grade.

We plan on having one of our village's inspectors stop by our home next week to look at it. My main question is: if the inspector balks, are there things I can suggest to overcome the stem wall's shortcomings? I have read about frost-protected shallow foundations. Even if I had to dig out around the exterior and apply XPS it would still be a lot easier than tearing this thing out and starting from scratch.

Thank you,


HI Brian,      I am (post #214615, reply #1 of 3)

HI Brian,

     I am wondering if when you removed the patio did that mean you are now left with the poured walls and a slab inside the walls on which the patio bricks were laid?  Or, do you have just the perimeter walls?  If you could include a photo that might be helpful too.  It is probably feasible to turn what you have into a code approved foundation for your addition, but based on the condition and amount of work needed it may not be smart or economical.  Unless access is very challenging, a new foundation may be the way to go.  Have the walls cracked or settled/heaved?  If they are still level and plumb there is a good chance the material under the footings is draining well/properly prepped.  Good luck.  Come back with more info if you'd like some more feedback.

I've only heard this (post #214615, reply #2 of 3)

I've only heard this described by an architect relative of mine, years ago.  And basically you'd have to get an engineer involved to certify it.

But basically you dig down a foot or so, then outward for maybe 4-6 feet, then install foam insulation, down the wall and horizontally out to the edge of the excavation.  (It tends to be done mostly in cases where the final grading has not been done and the final foot or so of topsoil has not been placed yet.)

Keep in mind that this scheme (if it's allowed at all) only works if the space above is heated year-round, vs "seasonal" like a 3-season porch, and any crawl under the space must be "conditioned", not vented.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Assuming the old stem walls (post #214615, reply #3 of 3)

Assuming the old stem walls are still in good condition you'll have to have an engineer certify to their strength, depth, how much rebar and where it's located and frost depth. By the time you're done trying to hae that done new footers will probably be cheaper and certainly better.

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.