The dreaded flooding basement is a real pain. Basements, as we all know, are notorious for being damp and having water issues. This is primarily because water moves in all directions underground, sometimes even straight up. Not to mention soil weights a lot more when wet placing lots of stress on basement walls leading to cracking and, you guessed it, water infiltration. In today's blog post, we discuss the best ways to keep your basement environment under control by keeping the moisture out.
Hydrostatic Pressure and Soils
Let's first discuss why so many basements have so many problems. By definition, hydrostatic pressure is the force exerted by a fluid, such as water, against an object or surface that is in contact with it. Hydrostatic pressure can cause water to seep through basement walls or floors, resulting in leaks and water damage. This pressure is created when water accumulates in the soil surrounding the basement and creates a buildup of pressure against the basement walls. The pressure can be further compounded by factors such as poor drainage, heavy rains, and soil saturation.
Clay, Sand, and Gravel
The amount of moisture that a soil can hold will depend on its makeup, which will also affect how heavy or light it is. For instance, clay soil will hold a lot more water than sandy soil. This is due to the size of the particles that make up the different soils. The ability to hold water decreases with granule size. For instance, gravel holds a small amount of water because water easily passes through it in between all the particles. Clay on the other hand has much smaller particles and is much denser. This density prevents water from passing through it quickly.
Waterproofing Systems
To prevent hydrostatic pressure from causing leaks in a basement, it's important to design a waterproofing system that can effectively manage the water pressure by moving the water out of the soil and away from the home, quickly and easily. This can be done by implementing several techniques and using superior products designed to keep water out.
Positive slope
The simplest part of a waterproofing system is a positive slope. A positive slope simply means that the ground surface is sloping away from your home, allowing water to flow away from the building or structure, rather than pooling or collecting near the foundation. A positive slope can be achieved by adding soil or gravel fill to raise the grade of the land near the house. This alone is not going to prevent water from entering your basement.
Gravel Backfill
Gravel backfilling is another simple and cheap technique that can drastically help with water intrusion. As we discussed above, hydrostatic pressure puts stress on your basement walls. This pressure can push water through any cracks that have developed in your foundation. Gravel backfill helps remove this pressure altogether. Gravel backfill is simply placing a large amount of gavel on the exterior of the basement wall to allow the water to flow quickly between the particles removing the pressure. The water is then directed to a drainage system at the bottom of the wall near the footing to allow the water to flow out and away from the foundation as quickly as possible. Many older homes and cheaply built homes have soil placed directly against the basement wall. If your contractor is placing soil directly against your foundation or basement wall, that's bad news. Soil against the foundation means the water after a rain is collecting and sitting against your basement for a longer period of time.
Waterstops
Most basement walls are poured concrete. Concrete naturally cracks as it dries which is why you see control joints placed in concrete slabs. This is to "control" the cracking by creating a small weakness in the concrete (plus it looks better). Unfortunately for basement walls cracking leads to water getting in your basement. This is where water stops come into play. Waterstops are long rubber strips placed at the control joints, in your concrete prior to the pouring of your basement walls. This flexible, rubber water-stop allows for the concrete to crack at the control joint while preventing water from getting in.
Side Note: Waterstops are more commonly found in commercial construction for some reason. This isn't the only product the residential world can benefit from.
Waterproofing Membranes and Drainage Tiles
Over the years the waterproofing industry has advanced leaps and bounds to keep water from entering your basement. From fluid-applied products to drainage mats there are a lot of systems out there to seal up your foundation and basement walls. In general, waterproofing membranes act as a barrier to keep the water from finding its way in. There are self-adhering products that are applied much like a giant sticker, and fluid-applied products, which are sprayed on or rolled on. These products are usually made from bituminous (a tar-like substance) that is flexible to allow for expansion and contraction without tearing and of course resist to water. These membranes, along with the gravel backfill ultimately lead water down to the drainage tile near the footing to be directed around the home and out to daylight usually to a nearby ditch.
Pro Tip: When inspecting your waterproofing be sure to look for a drainage "sock" around the drainage tile. This sock is a fabric placed around the tile that prevents granules from the gravel and soil from clogging the pipe over time.
In summary, basement waterproofing techniques and products are far better than they used to be. Knowing what these systems are and understanding how they work may help you critique your design team or builder on your next home.
© 2023 by Clements Wimsatt Architects PLLC
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