6 Essentials to Commercial Foundation Waterproofing
The major cause of many common foundation problems is water. Commercial foundation waterproofing systems are a critical component for keeping buildings dry. Like air control above grade, it is important to consider water control below grade as a system solution, not as a single component.
A properly installed and performing waterproofing membrane is important, but without a proper drainage system to allow the water to flow away, water can damage virtually any construction project. An improperly conceived waterproofing system can allow hydrostatic pressure to build, making any crack in the foundation vulnerable to water damage.
To properly protect a concrete commercial foundation, the wall must be sealed against the water, and the water must be directed away from the wall. Selecting an appropriate below-grade waterproofing membrane for commercial buildings is one of the most important aspects of maintaining structural integrity, indoor air quality, and comfortable living or working conditions for all occupants.
With that said, let’s dive into the details of six things to be aware of when tackling a commercial waterproofing job.
1. Understanding site conditions
In accordance with the 2021 International Building Code (IBC) section 1805.3.2, concrete or masonry walls that retain earth and enclose interior spaces and floors below grade shall be waterproofed – designed and constructed to withstand the hydrostatic pressures and other lateral loads the walls will be exposed to.
Therefore, when it comes to commercial waterproofing, it is important to understand the overall water management system goals for the site conditions. Soil quality, water table location, and how the system will be installed are all important considerations.
Different soils drain differently. Some hold tons of water, and others will let water filter through. A geotechnical report will help outline soils, possible contaminants and chemicals that may need to be addressed before selecting a below-grade system.
2. Hydrostatic pressure
The phenomenon of hydrostatic pressure is simply the weight of the accumulated water pushing against the structure.
If the soil surrounding a building is saturated with water, this places intense hydrostatic pressure against the foundation, allowing moisture to push its way through cracks and pores in the concrete walls and up through the floor slab. Four feet of water can exert nearly 300 pounds of pressure per square foot of wall.
Rather than seal a foundation against this pressure, it is more effective and more cost efficient to relieve, control, and manage. In other words, the best solution to hydrostatic pressure is to remove the water.
Commercial drainage systems redirect water away from the foundation, channeling it where it needs to go, but they are generally not enough protection. The inclusion of a footing drain (also known as perimeter drains) installed alongside a commercial waterproofing membrane offers the highest degree of protection. It will carry away all the water that has been directed down to it, helping to prevent continual build-up.
3. Capillary rise
Just as a dry sponge soaks up water, concrete walls have the capacity to wick moisture up from the footings.
As Dr. Joe Lstiburek from Building Science Corporation explains, the theoretical limit of capillary rise in concrete is 10 kilometers. So-called “capillary rise” is often a serious challenge in structures with concrete footings and concrete foundation walls. And according to Martin Holladay, capillary rise can contribute up to 15 gallons of water a day to a building’s interior moisture load.
Learn more about capillary rise…A Cup of Joe: Capillarity
Green Building Advisor explains that the phenomenon occurs when the forces of adhesion are stronger than the forces of cohesion. When the attraction between water molecules and molecules in the wall exceeds the attraction of water molecules to one another, capillary rise occurs. This capillary action causes moisture in damp soil to migrate first to the footings and then up into the foundation walls.
In many instances, moisture can travel several feet before the forces of cohesion and adhesion are in equilibrium. In a typical residence, capillary rise may add numerous gallons of water to the moisture load inside the home. The contrast in capillarity from one material to another can even be striking. Water may rise as much as 20 feet in certain clay soils, but only inches in crushed stone.
4. Capillary breaks
To avoid the adverse consequences of such moisture migration, a capillary break should be placed between the footing and the wall.
Architects, designers, and contractors have two primary options when it comes to capillary breaks between basement walls and concrete footings: membranes and fluid-applied waterproofing.
Contractors should follow manufacturer recommendations and wait before using fluid-applied products on new concrete footings. Some products may require up to a 4-week wait as the concrete must fully cure before application. The concern is that such products will be prematurely applied, potentially compromising effectiveness through improper bonding and even cracking. Of course, scheduling pressures are all too common. Architects that stipulate the use of a membrane applied while the concrete is freshly poured as a capillary break can avoid this problem.
Essential reading…How to Build a Dry Basement with Membrane Capillary Breaks
To facilitate the use of a membrane as a capillary break, a concrete wall should be keyed to a concrete footing through the use of a keyway. Vertical rebar can be employed for increased structural integrity when necessary and is typically required in earthquake zones. When vertical rebar is present, contractors often opt for fluid-applied products. However, membranes still remain a viable option.
Although claims have been made that the use of an appropriate concrete additive will reduce capillary rise, many manufacturers of such a product are unwilling to make such a broad promise. For a different solution, some builders choose polyethylene sheeting on the footings under foundation walls; however, bonding issues make this less reliable.
5. Specifying the right drainage board
Drainage composites are broadly specified as critical components of a successful below-grade commercial foundation system. However, they are often seen only as adjuncts to the main waterproofing or dampproofing course, tagged onto specifications as mere accessories. Too often treated as a commodity, drainage products are frequently viewed as interchangeable for one another without regard to their ability to meet the performance standards actually required of them.
Geocomposite membranes (i.e. drainage boards) available on the market today consist of two main components: an extruded dimple plastic core with filter fabric attached. The dimple cores are manufactured from one of two types of plastic; high impact polystyrene (HIPS) or polypropylene (PP). The fabric is usually a non-woven needle-punched polypropylene geotextile.
All drainage composites are not created equal. Often, specifiers focus on compressive strength and geocomposite water flow rates as the main criteria.
These are very important criteria, but reliance on just those technical criteria can result in less than desirable performance over the life of the structure. In addition, the savvy specifier should consider the durability and strength of the membrane, both during the backfilling process and over the life cycle of the building it is intended to protect.
The dimple portion of drainage boards are made from one of three main types of plastic: High Impact Polystyrene (HIPS), Polypropylene (PP), or High-Density Polyethylene (HDPE).
HIPS has the advantage of delivering high compressive strength ratings (according to ASTM D6364-06). However, on the downside, HIPS is not as durable as other plastics. Despite giving high compressive strength numbers in laboratory testing, it is subject to stress cracking over time when under load, leaving the critical waterproofing vulnerable.
Many designers will specify the drainage board by the compressive strength numbers without regard to the actual requirements of the projects. HIPS drainage boards are specified with, for example, an 18,000 lb/sf compressive strength required. But this requirement is because that is what the HIPS tests at, not because that’s what the project technically requires. For instance, in specifying a drainage board, one might see a requirement for a drainage board with 15,000 lbs/sf for a roof that is engineered for only a few hundred lbs/sf.
PP and HDPE will show somewhat lower compressive strength numbers (according to ASTM D6364-06), but will provide more durability, having more resistance to stress cracking under long term load. Unlike HIPS, neither can be torn by hand. Flow rates through the composites, though remain similar to or better than those of HIPS drainage boards. Both PP and PE can be more easily formed into other dimple shapes, patterns, and heights that will deliver appropriate performance at an appropriate cost.
This suggests specifications that focus on compressive strength as the primary performance criterion are not taking into account other important criteria.
6. Selecting a dimpled membrane
Dimple membranes can be an excellent choice for applications less than 12 feet (3.7 m) in depth with no hydrostatic pressure. These applications may be residential as well as multi-family or light commercial buildings where full waterproofing and drainage board systems would be overkill.
Dimple membranes create an air gap, producing a way for water to drain to the footing tile and diffuse hydrostatic pressure. Deciding on a dimpled membrane for a foundation’s protection system is arguably the right choice for most buildings. One of its key advantages is its ability to be installed over virtually any foundation type: poured concrete, concrete block, insulated concrete form, or preserved wood foundations.
Additionally, dimpled membranes offer many benefits that sprays simply do not. Dimpled membranes provide an even application, factory-controlled quality, and the ability to bridge foundation cracks. This means no water intrusion, optimal comfort and healthy living spaces for homeowners, and fewer warranty claims and call-backs for builders.
And when selecting a commercial drainage membrane, you should consider the following:
- What type of protection do you really need?
- Do you know the best/recommended way to install or secure the drainage membrane to the foundation?
- What accessories are provided, and how do they affect performance?
- How does this product stand up over time?
- Would you recognize the signs of a problem with your foundation protection?
- Do you know the damages that can result from a failed drainage membrane, or from an improper installation?
- Do you know the proper recourse should an issue/damages arise?
Essential reading…Is Your Dimple Mat Up for the Job?
The type of protection your clients or homeowners can expect depends a great deal on the quality of the drainage membrane you select. The dimple height, sheet thickness, and compressive strength vary between manufacturers. Understanding the true requirements for the project will allow the selection of the appropriate drainage board by calling for the appropriate performance criteria.
Selecting an appropriate below-grade waterproofing solution for commercial buildings is one of the most important aspects of maintaining structural integrity, indoor air quality, and comfortable living or working conditions for all occupants. A water-managed concrete foundation system prevents water build-up at the foundation wall. No hydrostatic pressure, no force. And without pressure, there is no need to worry about water seeping through concrete cracks and pores that will lead to mold and other moisture-related problems.
If you’d like to learn more about commercial building protection and water management, building science guru Dr. John Straube shares his insights on high-performance building, or move above-grade and learn air barrier design strategies for large commercial buildings.
And if you’re interested in below-grade dampproofing and waterproofing products specific to commercial applications, check out our full line of DELTA building envelope products and accessories.
