Page 231 - Construction Waterproofing Handbook

4.6 CHAPTER FOUR

FIGURE 4.1 Drainage board installed over the vertical waterproofing at the basement
level. Note the slope of the grading away from the structure and the French drain tube
installed to drain water collected by the drainage board away from the basement.

Groundwater control
As with commercial construction, anytime residential construction involves below-grade
spaces, it is mandatory that systems be installed to drain away from the structure as much of
the groundwater present as possible, including managing the surface water than permeates
the soil to below-grade areas adjacent to the structure. Removing as much water under hydro-
static pressure as possible from the basement area can eliminate many water infiltration prob-
lems merely by removing the water source before it has a chance to enter through the 1 percent
of the envelope that is most subject to leakage, namely, the slab–wall joint.
In residential construction this is usually accomplished by installing site-fabricated
French drain systems, as presented in Chap. 2. This application involves laying a perforated
pipe in a bed of loose gravel adjacent to the footing/foundation to allow water to percolate
into the pipe, from which it is drained away from the structure. The problem with such
applications, especially in residential construction, is that by the time construction is com-
pleted, the drainage system is often damaged or plugged by improper backfilling over the
drains and construction work that is allowed to take place over the drain field. It is not
unusual to find that these systems do not work by the time the home is completed. This
allows water to build up at the critical slab–wall joint, and if the detailing is not adequate,
water will infiltrate into the basement.
As recommended for commercial construction, prefabricated drainage systems are a bet-
ter choice in all residential applications. These prefabricated drainage systems withstand the
rigors of construction, including poor backfill operations, and allow water to be drained away
from the structure at the critical slab–wall juncture in particular. These systems are also