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Frost Heave on the Inside?

Frost Heave on the Inside?

Frost Heave on the Inside?

(OP)
Here is an interesting question that I have come across only twice, but is probably pretty common. In areas where the code dictates footing depth for frost requirements we designers provide adequate foundations at the proper depth. But for interior pads and footings, most residential structures are expected to be heated, so the footings are not down deep, because no frost is expected. But what happens when the home is expected to reach freezing temperatures for extended periods, even on the inside...like a summer cabin in the mountains?

I was looking at another post that talked about water, subfreezing temperature, and frost susceptible soils being the 3 factors that must be present to have frost heave. Does anyone else have input on this?

My question main question is: should we be dropping the footings in interior spaces if we anticipate noncondition interiors? Or will the prescence of the building be enough
to block frost?

RE: Frost Heave on the Inside?

Try solar design with South facing glass and good insulation/outsulation to prevent interior subgrade frost.  A layer of gap graded gravel beneath the slab can minimize the frost heave potential.

RE: Frost Heave on the Inside?


I work in an area where the typical design frost depth for footings is 4 to 5 ft. and have seen houses where the perimeter strip footings, interior column footings and/or basement slab-on-grades have heaved because either protection was not provided by the contractor during construction or the homeowners left for the winter and turned the heat off (after draining the pipes). Heave of the perimeter footings can result in cracking of the foundation walls, heave of the interior column footings resulting in floors/beams being lifted and in one case, the basement slab-on-grade had heaved up to 8 inches in places. Keep in mind, the perimeter footings are at most a foot below the level of the interior basement slab-on-grade.

Dropping the perimeter and strip footings is a solution, albiet an expensive one.

Testing of the soil might confirm it's frost susceptability.

Proper design and installation of a rigid type extruded polystyrene insulation combined with a layer of non-frost susceptible material will also work. Somewhat expensive, but usually less than dropping the footing level.


 

RE: Frost Heave on the Inside?

Bigmig

About 8 years ago I worked a forensic project that addresses this question directly.  Here's the short version.

Spec house, garage below, built in fall/winter, left unheated until sale in spring.  Cold temps penetrated garage floor slab and froze saturated fine grained soil below the 4-6" granular fill layer under the slab.  

Fine grain soils expanded under interior footings, lifted the support columns and moved the entire house 14 inches laterally off the foundation (see pic).  Oh yeah... in case you were wondering why the whole house moved, apparently the contractor didn't seem to think that fastening the floor joists to the sill was all that important.

Although there was a perfect storm of circumstances in this case, it does highlight why shrugging off those pesky  frost penetration issues might sometimes frost your assets instead.

Hope this has been helpful.
 

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