Page 225 - Masonry and Concrete

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

FIGURE 6-33
Vapor flow from soil. (from W. R. Meadows, Inc. The Hydrologic Cycle and Moisture
Migration).

crete slab or framed floor structure into the building. Vapor migration
from the soil, if unimpeded, can provide a continuous supply of
below-grade moisture flowing into the structure and then migrating
outward through the walls and roof. If cooled below its dewpoint, this
continuous supply of moist air will condense to liquid on interior sur-
faces, or condense as liquid or frost within the walls or roof of the
building envelope. Vapor flow into buildings from the soil is a primary
cause of the damp feeling often associated with basements.

6.5.3 Surface and Subsurface Drainage
Surface drainage should be the first line of defense in every residential
moisture protection system. Groundwater can be controlled to a great
extent by reducing the rate at which rainwater and surface runoff enter
the soil adjacent to a building. Roofs typically concentrate collected
rain water at a building’s perimeter where it can cause serious ground-
water problems (Figure 6-34 top). Water that is drained quickly away

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