All modern basements use some type of waterproofing system
to keep the space dry and moist free. Either on the backfilled side (positive
side) or inside face to the basement walls. As a minimum all basements should
have a high-quality positive side single membrane waterproofing system
installed as well as all the support items and products that are required by
the manufacture. Membranes should be installed under the slab and wrap up the sides
of the footings and onto the wall and properly terminated at grade.
Is Waterproof the
Same as Vapor Proof?
A basement with an approved, properly installed, and
inspected waterproofing system can make a basement waterproof, but does it make
the basement vapor proof? Some membranes are considered waterproof, but not
According to Lee Woolsey of Lowry Waterproofing Supply,
basements’ concrete mat slabs and walls can retain a lot of water captured from
wintertime construction exposure. Out-gassing of retained moisture can take a
year or more if enough water is retained and adequate ventilation is not
provided. Even properly installed waterproof membranes can “leak” vapor, but are
I have seen owners/contractors run heaters and dehumidifiers
to lower the moisture level in the basement space. At Palo Alto Concrete we have also applied
epoxy coatings to our concrete slab floors in order to stop any vapor from getting
through and potentially damaging expensive hardwood floors being installed. Flooring
contractors use moisture meters to establish maximum percentage of moisture allowed
on concrete slabs prior to installation of their wood flooring.
Each project has its own risk to water leaking in to the
basement space. Some basements are built over existing soil that is gravel in
nature and along with a comprehensive perforated pipe and drainage system at
the bottom the basement water pressure should be minimal and leaks a low risk. Other basements are built in a high water
table and the excavated hole needs to be dewatered during the construction
process. When completed no drainage
system will be installed and water will be wrapped around the basement
structure. These basements experience more water head (pressure) to the
membrane system and water stops and are at a higher risk of developing leaks. Each
project should be evaluated for site conditions, wall and footing design and
configuration, slab and wall penetrations and risk to leaking and if a positive
side vapor barrier is needed as well.
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