In most cases, waterproofing refers to spray-on coatings or peel-and-stick membranes, but contractors who specialize in keeping basements dry know that a successful waterproofing system is more than membranes.
It starts at the roofline with the eaves, gutters, and downspouts, and extends to landscaping, sprinklers, and ground slope. The below grade components—membranes, drain tiles, sump pumps, etc—must be specified to complement the products installed above-grade.
There isn’t a single product that will keep water out, whether it’s on a commercial roof or in a residential basement. It involves waterproofing, drainage, and landscaping systems that must work together.
Residential or commercial waterproofing systems should be evaluated from where the water enters: the roof. Is there a gutter system in place? Are the downspouts connected to extensions that direct the water well away from the foundation, or do they drain directly to the foundation?
Rain gutters can collect astonishing amounts of water in a matter of minutes during a typical downpour. (One inch of rain on a 2,000 square foot roof translates to 1,250 gallons of water!) If the rainwater or melting snow does not drain far enough away from your home, it will saturate the soil near the foundation and it can eventually seep into the crawlspace or basement. It may be heavy enough to actually crack basement walls when the soil is wet. Hydrostatic pressure is what causes this. To prevent water from collecting near the foundation or footing, downspouts should be directed onto a non-pervious surface that slopes away from the home or connected to drainage pipes.
The solution to most remedial waterproofing is on the ground, not below it. Nearly all residential waterproofing problems can be solved by addressing the soil type and slope around the foundation. (Exceptions are situations such as a home built on top of an underground spring or in an area with a water table closer than 10 feet to the surface).
Experts agree that controlling surface drainage is the single most important factor in keeping basements dry.
The ground around the home should slope downward (away from the structure) for a distance of at least six feet. It doesn’t have to be much; two inches over the six feet is sufficient to channel water way from the foundation.
Examine the landscaping, planned or in place. Do sprinklers soak the ground near the foundation? Do leaky hose bibs saturate the soil beneath them?
In the past decade or so, homes have increasingly been built on hillsides or other marginal land that was passed over by developers years ago. Homes built on hillside lots are often problematic for waterproofers, as they’re sometimes in the path of all the water collected on an entire hillside.
If the water can’t be directed around the structure, a second line of defense is sometimes needed. This consists of a drain tile —a perforated pipe set in gravel a few feet below the surface or equivalent—set perpendicular to the slope of the hill a dozen feet or so uphill of the home. Water traveling down the slope will fall into the drain and be directed away before ever reaching the waterproofing barrier.
Concrete basements are now required to have a waterproof barrier installed nearly everywhere in the country. Your area’s soil type and expected precipitation will determine the level of protection you need. Across the country, millions of houses were built when codes only required damp-proofing, or none at all. In many cases, these asphalt-based coatings were literally brushed on with an old broom, and after years of wear have degraded to the point that they no longer function.
If all of the above-grade components check out, and the basement is still damp, any solution will likely involve applying a new waterproofing barrier. These can be spray-applied, a peel-and-stick membrane, or even a slurry coat troweled onto the wall. In every case, they work by preventing water from penetrating the foundation walls.
For new construction, integral waterproofing admixtures may be worth investigating. These work by making the concrete itself waterproof. Integral waterproofing slurry coats are also available for remedial work.
The choice of waterproofing products usually comes down to cost, effectiveness, and the homeowner’s level of confidence in the applicator.
Regardless of the type of waterproofing applied, it’s usually covered with a drainage system of some sort. The most basic option is washed gravel. Many opt for a rigid or semi-rigid insulating drainage board; they’re light weight, protect the waterproofing membrane during backfilling operations, and insulate the below grade living space.
Sheet drains, or dimple membranes, are another option. Made by at least half a dozen companies, they’re available in a wide range of sizes, compressive strengths, flow rates, and filtration capabilities. A few dimple membrane manufacturers claim that their product can fill the roles of both a waterproofing and drainage component.
At the base of the foundation, a footing drain must be installed to move the water away from the structure. In the past, the solution has consisted of a perforated PVC pipe, buried in washed gravel and covered with straw to prevent soil from clogging the system. This system works, and is still used frequently. Prefabricated footing drains also work well. A few manufacturers offer their dimpled sheet drain and drainage tile in a single product to make installation easier.
Effective control of water from the roofline to the footer will resolve nearly all moisture issues. In a few cases, though, the source of moisture issues may be coming from beneath the structure. These isolated instances can only be resolved through the use of an underslab barrier. Mostly used in new commercial construction, these heavy-duty sheets prevent moisture from migrating through the floor slab into the building’s living space.
Once water has collected at the footings, it needs to be directed away from the structure. In most cases, this means installing or repairing the sump pump, which moves the water to either to a French drain placed well away from the house or into a storm water drainage system.
The sump pit should be sized to your climate. It needs to be large enough that the sump pump doesn’t need to run constantly to keep it empty, but not so large that it takes an inordinate amount of space.
The size, type and power source for sump pumps will depend on the application. Some are hard-wired directly into the home’s electrical system. Others offer battery back-up, or audible alarms when the water gets too high. A few can even be programmed to dial your cell phone if something goes wrong.
One final area to check for problems is the French drain, or dry well. Decades ago, these were made from 50-gallon metal barrels with holes punched in them. Over the years, they may have rusted and collapsed. If so, they’re easily replaced with plastic drywells available from a variety of manufacturers.
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