Waterproofing Systems & Risks


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 “vapor proof”.

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 still waterproof. 

Various Solutions

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.

Various Risks

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. 

How Can We Help?

Palo Alto Concrete & Construction can design the right waterproofing system for your basement project from lower cost single membrane systems to multi-layer membranes, multiple water stops and epoxy injection systems. We can also provide waterproofing consultants that will design, specify and inspect the waterproofing installation work