Underground drainage to daylight, including how it fails

The idea is simple. Instead of the downspout ending at an elbow near the wall, it drops into a fitting at grade and continues underground, running on a fall, to an outlet somewhere down the slope where the water can leave on open ground. The technical term for that outlet is daylight, because that is literally what it is: the point where the pipe comes back into the open air.

Done properly it is the most complete answer to the last ten feet available. There is nothing to mow round, nothing to kick out of alignment, nothing to flip up in spring and forget to flip down, and the discharge point can be a long way from the house.

What makes one work

Fall, all the way. The line must run downhill continuously from the house to the outlet. A buried pipe with a dip in it holds water in the dip permanently, which collects sediment and freezes. This is the single most important thing about a buried line and the thing most likely to be got wrong by whoever installed the one already in your yard.

Somewhere to come out. There has to be a point lower than the inlet, on ground you control, where water can be released without creating a new problem for you or a neighbour. On a flat lot this is the hard part, and on some flat lots the honest answer is that a daylight line is not possible.

Smooth pipe, not corrugated. Rigid smooth-wall pipe flows better, resists crushing, and does not trap sediment in every corrugation. Flexible black corrugated pipe is cheap, quick and everywhere, and it is the material most often found collapsed or silted solid when an old line is dug up.

A way to get into it. A cleanout, or at minimum a removable connection at the downspout, so the line can be rodded or flushed. A sealed buried pipe with no access is a pipe you will eventually have to excavate.

A proper outlet. A pop-up emitter or a grated outfall, set so it cannot silt over and cannot be mown flat, in a spot where the discharge will not scour a channel.

Freezing, in this climate

People ask whether a buried line freezes in a St. Louis winter. It can, at the ends. The pipe in the middle of the run is generally below the surface and moderated by the ground. The vulnerable points are the outlet, where the pipe is shallowest and open to cold air, and the inlet fitting at the downspout.

A frozen outlet on a January morning is usually a nuisance rather than a disaster, because the volumes of water in winter rain are typically modest and the ice usually clears within a day. It becomes a real problem when it coincides with a rapid thaw and heavy rain on frozen ground, which is a scenario this region does get. Mitigations are ordinary: keep the outlet clear of leaves and grass in the autumn, do not set the outlet in a hollow that already collects standing water, and consider an overflow arrangement at the downspout so a blocked line spills at the top rather than backing up into the trough.

What to expect when it is installed

• A trench. It is excavation, so there will be a visible line across the yard for a season while the sod knits back. Anyone promising an invisible install is describing the finished state, not the first month.
• Utility locates. Before anyone puts a shovel in the ground, buried services get located. This is not optional and it is not a delay tactic.
• A decision about how many downspouts share a line. Combining several into one pipe is often sensible and sometimes undersizes the line. That depends on roof area, which brings you back to sizing.
• Tree roots as a live consideration. A line run near mature trees will meet roots eventually. Routing matters.
• Something you can see working. Ask to be shown the outlet running with a hose before the crew leaves. If it does not run visibly with a hose in the top, it will not run in a storm.

Above ground or below it, the test is the same one. Walk to the place where the water leaves, point at it, and say the sentence out loud. If you cannot point at it, that is the finding, and it is the finding on a great many houses in this metro.

When it is not the right answer

On a flat lot with no available fall, a daylight line is not physically possible and anyone who sells you one anyway has sold you a buried reservoir. On a small lot with the house close to a boundary there may be nowhere to discharge that does not become a neighbour's problem. And where the real fault is grade sloping back towards the house, the buried line is treating a symptom while the yard keeps delivering water to the wall.

In those cases the honest options are surface extensions, regrading, a dry well or a system that a drainage or excavation contractor should design, and that is what we will say. Keys does roofing, gutters and downspouts. That includes reroutes, extensions and underground drainage. It does not include pretending every lot in St. Louis can be drained to daylight.