Case Study - Basement Drainage - Washington D.C.

In November of 2010, we had the opportunity to design and install a basement drainage system at a residence in a suburb of Washington D.C. It is quite a distance for a drainage contractor to travel, but we were requested by an existing customer to take on the project. We have installed a number of successful drainage solutions throughout the customer’s portfolio of apartment buildings in Texas.

Alan Weaver, one of our drainage specialists, flew out first to gather measurements, evaluate the problem, and construct an effective drainage design. Given the amount of subsurface water that was entering the interior through the cinder block walls, it was evident that a French drain with a moisture barrier would be needed on three of the exterior walls. The trenching would be done by hand and some of it would require excavating to almost 6’ deep, a potentially dangerous job if the trench sides are not professionally shored. Drainage Case Study - Washington D.C. 1
So after a month of planning, the drainage installation crew loaded up all the equipment and virtually all the materials that would be needed, and went on their way to the job site, 1,340 miles away. It took two days of driving each way and six days at the site, but all went well. Drainage Case Study - Washington D.C. 2
The French drain we installed was relatively straight forward. We excavated to a depth of 12” below the interior floor elevation and adhered a moisture barrier material called Polyguard 650 (http://www.polyguardproducts.com/products/architectural/650waterproofing.htm) to the outside wall. We then installed a perforated PVC pipe in the bottom of the trench, lined the trench with filter fabric, and backfilled the bottom 12” of it with large aggregate gravel. A “waffle” type drainage mat, also manufactured by Polyguard, was then placed against the wall and the trench was backfilled with native soil. The matting is designed to keep a narrow space open from top to bottom to allow water to easily flow downward towards the perforated pipe. The perforated drainage pipe will collect any water that flows towards the house and down through the mat. The pipe is sloped towards the front yard bar ditch, where the elevation dropped sufficiently enough to allow for a gravity discharge there.

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There have been a number of precipitation events since the system was installed, and they have proven to be good tests for the system.

“My family in the DC area has visited the house after reasonably big storms and report that the basement stayed dry. It is their opinion that the drainage is in fact fixed. Thanks for taking care of this.”