The best and most effective way to waterproof a basement is with french drains. The concept is very simple, direct water below the foundation and into a sump pit with a pump, relieving hydro static pressure that’s up against the walls and floor, creating a healthier, drier basement. It’s not rocket science, but it’s a job that you’ll never want to do twice (especially if you have a finished basement). These systems need to work reliably for decades (we guarantee ours for life). This requires experience, ingenuity, and thorough inspections to understand the unique conditions affecting the basement, and how the walls, floor, and footing intersect.
“Low Profile” systems are ideal when you are dealing with water in and up against the walls with little to no water table in the basement or crawlspace. The primary function of this drain system is to allow water that is in or up against the walls to pass to the underside of the slab and into the ground. If there is an abundance of water, it will enter the pipe and work its way to the sump pit.
“Standard” french drain systems should start at a 7″ depth and pitch to a 9″ depth as it terminates at a sump pit. Most commonly installed with a 3″ perforated PVC pipe. Sometimes we come across systems with the holes facing down that have failed. With the holes facing down rising ground water has much less clean crushed stone to filter through before it enters the pipe. While not an issue at first, years and years of additional sediment can lead to premature failure of the system. With the holes facing up, water must filter up through much more stone before entering the pipe, bringing considerably less sediment with it.
“Premium” french drain systems that are buried starting at 8″ and pitched 12″ to a sump pit. These systems perform identically to our basic system other then they lower the water table that much more. Deep systems should not be installed when you have and older home with no footing. Digging that deep can destabilize the soil that the foundation rests on. If there is a footing this is not an issue at all.
Although not a french drain, above slab drainage systems are can be part of a solution when the floor shouldn’t be broken around the perimeter (i.e. monolithic foundations). These systems allow water penetration in the walls, and between the wall and floor to travel down a channel or behind a “base board” that is epoxied to the floor, and into a sump pit. These systems will have no effect on hydro static pressure against the floor, and it’s a good idea to pair these systems with a dehumidifier.
Some foundations are plagued with excessively wet and muddy soil or iron bacteria in the ground. Make sure to use filter fabric! The fabric should rest on the floor of the trench and up against the dirt on the sides of the trench if necessary. Care should be taken to make sure that the fabric does not wrap around the pipe. When dealing with very high amounts of iron bacteria it may be wise to not install a check valve and design a discharge setup that can work efficiently without one. Regular maintenance will always help a system perform better for longer, more so for systems dealing with iron bacteria and mud.
Every now and then we come across black “ADS” pipe, and to our surprise there are still contractors out there that use this product for interior french drain systems. This is a flexible pipe that has narrow slits all around the pipe. These slits are prone to clogging up and as this occurs it continually accelerates its degradation until it fails. This pipe was popular in the 80’s because of how inexpensive it was and how easy it was to install, its shortcomings would not become apparent until years after many of these systems where installed. Sadly because of how easy it makes installing a drain system, and how inexpensive the product is, it continues to be used, mainly by construction companies who install drain systems during the construction of a new building, not professional waterproofers.