Downspouts and Your Foundation: The Cheapest Fix in Pittsburgh
Every wet basement in Pittsburgh has a story, and most of them start at a downspout. Not a cracked foundation, not a high water table, not the neighbor's grading — a downspout that ends eight inches from a stone wall and delivers a few hundred gallons to the same spot every time it rains. Fixing that costs less than a nice dinner. Waterproofing a basement from the inside costs $8,000 and up. Start with the cheap end.
How much water we're talking about
A 1,000-square-foot roof plane collects about 620 gallons from a one-inch rain. If that plane drains to one downspout, that's 620 gallons landing in a spot the size of a dinner plate. Pittsburgh gets 38 inches of rain in a year, so that one downspout puts roughly 23,000 gallons against the foundation annually, plus whatever the 28 inches of snow turns into in March.
What the ground here does with it
Most of Allegheny County sits on clay and shale, and much of it on a slope. Clay doesn't drain; it holds water against whatever's next to it, which on a hillside lot is the uphill foundation wall. Shale sheds water sideways along its bedding planes, which is how water that lands at the front corner of a house in Brookline ends up coming through the basement wall at the back. And the county's famous red beds — the soft red claystone under a lot of the hillsides from Mt. Washington to the North Hills — turn to mush when saturated. Allegheny County has more landslides than any county in the state, and a lot of them start with roof water dumped at the top of a slope. If you have a retaining wall on the downhill side of the house, the water from your downspouts is the load it wasn't designed for.
The old clay drains
Half the houses built before 1960 have downspouts that disappear into the ground. Originally they ran through clay tile pipe either to the street, to a dry well, or — very commonly in the city and the older suburbs — straight into the sanitary sewer lateral. Sixty to a hundred years later, the tile is cracked or collapsed, roots have found it, and the downspout is quietly dumping its water underground right beside the foundation. From the surface it looks fine.
Two things to know. First, Allegheny County and most of its municipalities now prohibit roof water in the sanitary sewer, because it overloads the treatment system and causes overflows into the rivers. Many municipalities, including Mt. Lebanon, require a dye test when a house is sold to prove the downspouts aren't connected; the Allegheny County Sanitary Authority's site explains the background. Second, a downspout into a dead drain is worse than no drain at all. If you don't know where a buried downspout goes, have someone run water through it and see whether it comes out anywhere.
The fix, in order of cost
- Extensions to the surface. A rigid aluminum or PVC extension carrying the water six feet or more from the wall, ending on a splash block on ground that slopes away. $25–$80 per downspout. This alone fixes more wet basements than anything else on this list.
- Redirect a dead buried drain. Cut the downspout above grade, cap the old pipe, and extend to the surface. $100–$250.
- A buried line to daylight. On a hillside lot, a 4-inch solid pipe from the downspout, run underground to a point where it can discharge downhill of the house. $300–$800 per downspout depending on length.
- A dry well. Where there's no downhill and the yard is flat — parts of Monroeville and Moon Township — a gravel-filled pit or a plastic chamber that lets the water soak away slowly. $600–$1,500.
- Regrading. If the ground slopes toward the house, the downspout fix only goes so far. A yard of topsoil sloped away from the wall is a landscaping job, but it's still cheaper than waterproofing.
Where the water should end up
Six feet from the foundation is the minimum. Ten is better on clay. On a slope, downhill of the house and downhill of any retaining wall. Never onto a neighbor's lot, never onto the sidewalk where it freezes, and never into the sanitary sewer.
The quick check
Walk around the house in the rain with a flashlight. Every downspout should be discharging somewhere you can see, onto ground that carries the water away. Any downspout that goes into the ground: note it and find out where it goes. Any downspout ending on a splash block that's been kicked crooked: fix it. This takes ten minutes and it's the first thing we do on any gutter repair visit. If a downspout has come apart at the elbow or crushed at the bottom, that's on the same visit. And if the gutters above are overflowing, the downspout is only part of the answer — why gutters overflow covers the rest.
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