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Below Grade Waterproofing – Doing It Right The First Time Around

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Modern commercial and residential buildings often include spaces below ground level. The areas below the grade level are often used for parking, utility rooms, storage for maintenance and tunnels for services and communication conduits. As part of the building foundation, the performance of this part of building enclosure is vital for structural integrity and life cycle costs.

What is Below Grade Waterproofing?

Below-Grade waterproofing is the construction practice of applying membranes and coatings to the foundation walls of the structure under street or ground level, as part of the building envelope.  It can go by other names such as below-ground or basement waterproofing.

Effective waterproofing and water management techniques goes hand-in-hand to keeping the below grade areas leak free. An astute project owner would ask: What below grade waterproofing methods and processes should be used to ensure the quality and performance of the finished building(s)?

Having an expert waterproofing team in Los Angeles and Southern California, Xpera Group offers to give you objective, experience-powered guidance when it comes to waterproofing your building for longevity and lasting safety. Feel free to reach out to us to discuss your needs. Here we will explore below grade building envelope in new construction.

Effective coordination in design phase

Since below grade waterproofing should ideally last as long as the building (remedial waterproofing solutions can be prohibitively expensive), you don’t just want to prevent the water from penetrating into the building foundation – you want to control the water in the first place.

Below grade waterproofing design relies on two sources of information – the land’s soil & underground water conditions and the building’s foundation design. The water management for below grade starts from the work of a geotechnical engineer, who performs soils testing early to find the water table level, if there’s contamination and other factors such as salt deposits. That information gets handed off to the structural engineering firm where they design the foundations to handle the calculated hydrostatic pressure and the load of the building.

With this information on hand, the building envelope consultant is brought in to review the plans and coordinate the details with the project’s geotech, structural, and architect professionals. This includes checking the compatibility of materials, calling out incomplete specifications and more. When change orders come in during construction, if it pertains to the building enclosure, the consultant will also review them to verify it doesn't create waterproofing performance issues.

Below grade waterproofing in the construction phase

During the construction, a successful below grade waterproofing system will include a combination of effective drainage and impervious membranes applied on the foundation.

There’s a variety of perimeter drain systems that can be applied. Which is best for your building depends on factors like:

  • the ground slope around the foundation
  • the type of soil
  • irrigation systems used on landscaping
  • the material that the building foundation was made from
  • the design of the building

Drain systems can be installed both outside and inside, in which case they are used in combination with bio filtration.

There are two types of below grade waterproofing methods depending on the place of application – positive-side waterproofing and negative-side waterproofing. Positive-side waterproofing is done on the side where hydrostatic pressure is applied. In the case of below-grade waterproofing, positive side is the outside surface of the foundation, closest to the soil, and the negative side is on the inside.

Positive-side waterproofing includes: fluid-applied seamless membranes, sheet systems, hybrid systems combining a fluid-applied membrane in conjunction with an integral fabric, and bentonite clay.

It’s important to note that dampproofing solutions applied on the positive side are NOT considered waterproofing methods by UBC Code. They are inexpensive treatments based on bitumen or cement and are designed to prevent water from moving through the tiny capillaries in masonry and concrete, sometimes even against gravity.

Positive-side waterproofing is preferred over negative-side methods, because it’s more effective. Negative-side waterproofing methods redirect water after it penetrates the foundation. These solutions are best used with positive-side methods because it’s impossible to ensure the structural integrity of the building or structures close to the foundation without a way to keep water out of the foundation wall assembly.

One of the negative-side waterproofing methods is coating the inside of the foundation in acrylics, crystalline or latex additives, either as part of specialized sealant products or in a cement/sand mixture. Negative-side methods also include remedial crack injections. However, with crack injections it’s highly likely that the water will find another weak spot to penetrate.

What if below grade waterproofing was not done correctly?

Because the areas below grade are subject to extreme loads (carrying the whole structure), deterioration at those places can greatly reduce the serviceable life of the structure. Some signs that there is water damage to the foundation are:

  • paint that blisters or peels
  • damp patches
  • dribbling water
  • mold and mildew
  • wood rot
  • rust
  • odor
  • cracks
  • efflorescence (white powdery deposits)

The first signs of water damage to the foundation should prompt into action. The longer the potential damage is ignored, the more devastating the consequences can be. In extreme cases a failed system can lead to a flooded building.

If you’re in Southern California, call Xpera Group

Xpera Group is a team of 50+ professionals from the built environment. Our building envelope specialists frequently work on large scale waterproofing projects and their combined experience spans lifetimes. If you’d like to tap their expertise for your commercial or multi-family project or property, please feel free to reach to us today!   


Topics: Building Envelope, Waterproofing Systems, Quality Assurance

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