French drain no match for roof water

Alternatives for diverting runoff

Bill and Kevin Burnett
Inman News™

Not long ago we responded to a reader with a question about whether a half-round pipe she discovered in her backyard was in fact a French drain.

We speculated that it might be a feeble attempt to redirect groundwater from the house, but it was definitely not a French drain. We explained that a simple French drain was a trench filled with gravel used to control groundwater.

We suggested that the drainpipe could do double duty by collecting roof water during rainstorms and channeling water into the drainage system. This raised the hackles of two readers, one a landscape contractor, the other a landscape architect. Both said dumping roof water into the French drainage system is a bad idea. On reflection, we agree.

The purpose of a French drain is to direct groundwater away from the foundation. The filtration cloth, perforated pipe and drain rock allow groundwater to percolate to the pipe, and with the proper slope to discharge it away from the foundation. The volume of water discharged into the system during a heavy rain risks directing water toward the foundation instead of away from it.

It’s better to move water away from the foundation either by extending the ends of the downspouts far enough into the yard, or discharging the rainwater into a solid pipe that discharges downhill into a sump or collection area. It’s OK to place the solid pipe in the same trench as the perforated pipe. The perforated pipe should rest on the bottom with pipe holes pointed downward, topped by a layer of gravel, then the solid pipe, more rock and finally a top layer of sand.

The pros didn’t like our suggestion to place a 2-inch bed of rock under the pipe, but a number of cities require it in their local building codes. We go with the cities. The purpose of the filter fabric is to keep fine materials out of the pipe. In our view there is no quicker path to system failure than for the pipe holes to plug.

Finally, one pro took issue with our statement that digging the trench is a "fair amount of hard work," countering: "It takes an enormous amount of extremely hard work." We’re not going to argue about degree.

In another column we responded to a reader with a sticking door. We told him how to adjust the door to cure the problem. In response to this column a hinge manufacturer had another solution: an adjustable hinge. Kevin put this new-on-the-market product through its paces. We like it. It’s a piece of cake to install and adjusts easily up to about 3/16 inch side-to-side and up and down. Check it out at www.adjustabledoorhinge.com.

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