Frost footing pros verse joes

picture-76.jpgTouch on a picture to enlarge

You are looking at 2 cross sections as to how to build a frost footing.
The first picture shows how 98% of all house frost footings are installed. With this type of design there are some problems.
1. Where there is a 42” frost footing required the install 1-7 1/2” high footing 4- 8” blocks which = 40” with mud joints 41 1/4”. If they install a 1/2 high block the total height is 44 3/4” no problem except the code requires the grade height to 8” lower than wood framing and or wood siding. Making the frost footing only 41 1/4 with a high block and no wood siding. But you house has wood siding and no half high block the frost footing is now 36 1/2”. So in picture 1 the water is up to the top of the soil on the exterior. When it freezes in the winter we know water will expand and increase its mass crushing the insulation decreasing the R-value and allowing the water to freeze to the footing, which will move it, laterally inward or vertically which ever is easier.picture-78.jpg
2. As the temperate of your frost footing drops in the winter your concrete slab will also reflect how cold it is outside.
3. The Rigid foam insulation must be covered because the ultraviolet light from the sun will break down the insulation most contractors cover it with aluminum sheathing. Aluminum and does not like concrete or salt, it will corrode and eat the aluminum. Yet they pour concrete up against the aluminum shield and don’t tell the owners of the houses not to salt their sidewalks.

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