Foundation
Drainage
Foundation drainage is used in Residential
Foundations,
consisting of two separate procedures:
- Perimeter
draintile properly placed on the OUTSIDE of the wall,
next to and no higher than the top of the footing.
- Installation
of an exterior drainage insulation board.
As we know, Minnesota was a masonry block basement market
for many years. An important part
of the Waterproofing System was the draintile placed next
to the footing, beneath the floor. This draintile drained
water from the hollow cores of the block and therefore was a part of the water control system.
With
modern codes, these cores are often filled with grout and
will not carry water, making them useless.
The primary function of draintile is to relieve hydrostatic
pressure
on the exterior of
the wall; this will not happen if the draintile is placed
on the inside, below the floor. Exterior
draintile should be socked or filtered 4” plastic
and installed next to and no higher than the
top of the footing. There should be 6” to 8” of
rock placed on top of the draintile and up the wall. The
rock bed should be covered with a filter fabric. If draining
insulation were used on the exterior wall, a poly film
cut off sheet would be placed over the rock bed rather
than a filter fabric.
High Performance Waterproofing Systems
Through
our years of experience we have found the best performing
steps of all drainage systems
to be the following: Subfill below slab with 4” to
6” of
washed rock, sleeve the footings from
inside to outside every 6’ to 8’. Connect to
interior radon sump basin and, if possible
tie to a drainage Waterproofing System which will assure
a dry, usable basement.
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