It is important to understand the differences between exterior waterproofing and an interior drain system for foundations, as some may think that both are considered means of waterproofing. Exterior waterproofing stops the water from the exterior and prevents it from entering the foundation, where as an interior drain allows water inside the foundation, is collected, and then discharged outside by either gravity or a sump pit and pump. Therefore, an interior drain system is not considered waterproofing, but rather a means of water control.

Interior Drain

There are several types of interior drain systems, with the next to footing being the preferred system as opposed to the top of footing system. The next to footing system allows for the collection of water not only from through the wall but also from beneath the footing and slab. This is a much more effective way to collect all the water, as opposed to the top of footing system, which will only collect water that is intruding through the wall. The disadvantage of an interior drain system is that the system does not prevent the build up of hydrostatic pressure, which can compromise the structural integrity of the foundation walls. Interior drains should typically be used as a last resort and when exterior waterproofing is not feasible. This could include porches, driveway, limited site access, and other obstacles that would prevent exterior waterproofing. An interior drain system for collecting and discharging water can be a cost-effective means of water control if the obstacles prevent exterior waterproofing.

Exterior Waterproofing

Exterior waterproofing consists of installing a drain board over a waterproofing membrane on the exterior of the foundation wall and wraps down into an exterior foundation drain. As the water passes through the soil it comes into contact with the drain board and migrates down into the foundation drain, which typically discharges to daylight at the lowest portion of the property. With exterior waterp

roofing the hydrostatic pressure is not eliminated, but it is greatly reduced. By preventing the water from coming through the foundation walls, it also prevents the degradation and water staining of the foundation walls that occurs over time from the water intrusion.