Page 243 - Masonry and Concrete

Footings, Foundation Walls, Basements, and Slabs
242 CHAPTER SIX

the perimeter of the building effectively blocks the natural radial heat
flow paths (Figure 6-46). Heat migrating from the building interior ele-
vates the soil temperature above its winter norm and artificially raises
the frost depth. Seasonally fluctuating temperatures eventually stabilize
since the heat cannot escape to the exterior ground surface. Code
requirements for the use of frost-protected footings are based on climatic
conditions. The air-freezing index in Figure 6-47 indicates the magni-
tude and duration of winter conditions in various parts of the country.
The table and diagrams in Figure 6-48 list Code requirements for R-
value and insulation dimensions based on air-freezing index ratings.

6.9 Ventilation and Radon Protection

Crawl spaces must be ventilated to dissipate soil moisture vapor and
prevent its being drawn into the home. This means providing open-
ings in the foundation walls of sufficient size and number to meet code

INSULATION BLOCKS
HEAT LOSS

FIGURE 6-46
Frost protected footings.

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