The rubble stone foundation walls wept every time it rained, creating a dank, humid basement. The destructive power of ice dams, and a huge, overhanging elm tree created maintenance issues, leaving our clients unwilling to replace the gutters original to the old two-story house. The lot sloping to the rear left the downhill neighbors’ yards saturated much of the year. How were we going to solve these problems? By installing a ground gutter system.
A ground gutter is similar to the French drains familiar to most builders, with a few additional components. On this project, we started by digging a trench along the foundation wall, 12 in. deep at the front and pitching 1/4 in. per foot toward the back of the house. The trench is 24 in. wide, enough to catch rain falling from the eaves. We lined the trench with 0.060-in.-thick EPDM, a rubber roofing product (thinner 0.040-in. EPDM can be purchased from landscaping suppliers). We didn’t attempt to attach the membrane to the stone foundation but took care in keeping it close to the wall as the trench was filled.
An Underground RoofFixing Those Drainage Problems, 30 Years LaterFHB: Inground gutters keep basements dryGBA Encyclopedia: Inground GuttersGBA Encyclopedia: Stormwater ManagementGBA Encyclopedia: Roof GuttersGBA Detail: Underground Water Barrier Retrofit
At the bottom of the trench we laid 4-in. perforated PVC pipe directly under the roof’s drip line. Where the pipes join and change direction we installed distribution boxes with removable covers, providing access in the event of a clog. At the distribution boxes we also tied in 6-in. solid PVC drains. We connected this to downspouts from the one section of gutter we did install on the addition roof, which is easily accessed and ice-dam resistant. We filled the trench with 3/4-in. washed crushed stone, placing a layer of permeable landscape fabric about 2 in. below the surface to keep silt and debris out of the trench.
The drains tie together into a single 6-in. perforated PVC line that leads to a dry well 8-ft. x 12-ft. x 5-ft. deep. The dry well is lined with landscape fabric and filled with 11/2 in. crushed stone. We covered the crushed stone with more fabric, a loam/compost mixture for a planting bed, and a layer of partially decomposed bark mulch. The dry well should be able to handle up to an inch of rain before filling up. The few times a year that the dry well reaches capacity, the excess rainwater will exit via a 6-in. outflow pipe just below grade.
The outflow pipe leads to a back corner of the property, where it exits onto riprap (6 in. crushed stone) to prevent erosion, behind a swale. Not only will this keep the neighbor’s yard dry, the rainwater will have several hundred feet of forest to be absorbed into before reaching a river. That’s a big improvement over the original gutters, which fed into the municipal storm drain—and directly into the river in big storms.
What our clients are happiest about, though, is their dry basement.