Key takeaways
- An inch of rain on a 2,000-square-foot roof is over a thousand gallons, all of it arriving at the downspouts.
- Downspouts should discharge well away from the foundation, by buried line to a daylight outlet, pop-up emitter, dry well or storm connection.
- Buried downspout lines fail by crushing, separation, roof-grit clogging and root intrusion.
- Never tie downspouts into a footing drain.
The volume
Rain on a roof is concentrated into a few points. A 2,000-square-foot roof receiving one inch of rain sheds roughly 1,200 gallons, and a hard Puget Sound storm delivers that in hours. If the downspouts dump at the foundation, that water goes into the backfill against the house, which is exactly where you don't want it. Moving it away is the single most effective thing you can do for a dry crawlspace.
Where it should go
A buried solid pipe from each downspout, sloped away from the house, to one of: a daylight outlet downhill where the water can run off harmlessly; a pop-up emitter in the lawn well away from the house; a dry well in soil that actually drains; or a connection to a storm system where the jurisdiction allows it. Which one depends on the lot. On a sloped lot daylight is easy. On a flat lot in till, a pop-up emitter at a distance or a storm connection; a dry well in hardpan just fills.
How buried lines fail
Corrugated pipe crushes under a vehicle or settling fill. Joints separate as the ground moves. Roof grit, needles and leaves wash in and clog low points. Roots enter at joints and fill the pipe. The buried end, if it was a daylight outlet, gets buried under landscaping and the line backs up. Any of these shows up as a downspout that overflows at the elbow in a storm, or water pooling at the base of the downspout, or a wet crawlspace below it.
Replacement
Test each downspout with a hose and find the failure. Excavate the bad section or the whole run. Replace with solid PVC or HDPE, not corrugated, on a continuous grade with a cleanout where it's useful. Rebuild the outlet. Backfill and restore the beds. It's quick work and it often gets done alongside a footing drain repair or a French drain on the same property.
Written by the crew at 360 Leak Finders
We locate, excavate and repair buried water lines and exterior drains across Kitsap County, 24 hours a day. If this guide raised a question about your property, call (206) 354-9906.