How water leaves a rowhome roof
Per the Rowhouse Manual, water at the front (and sometimes the back) usually runs into a roof drain or a scupper, an opening through the parapet or cornice, and from there into an outside downspout. At the back it often runs off into a gutter along the rear wall that feeds a downspout. A main roof and a rear addition may drain separately, so ask your roofer to point out every outlet.
Where the water ends up matters too. The manual says the final destination has to be on your property: it's illegal to send roof water onto the sidewalk, the street or a neighbor's property, partly because it freezes into ice. It also says current code wants it in the sewer line, either through the cast-iron boot at the bottom of the downspout or through the lateral pipe in the basement. A downspout emptying onto the pavement is a problem to fix, not a quirk of the block.
What you can check from the ground
- Watch during a heavy rain. Water spilling over the cornice or the rear gutter instead of coming out of the downspout points to a clog at the outlet or in the pipe. The manual's maintenance list says to look for clogged gutters and downspouts during heavy rain.
- Look at the downspout and its boot. A pulled-apart joint, a cracked section or a wet stripe on the brick beside the pipe means water is escaping before it reaches the sewer. The National Park Service's roofing brief notes that outside downspouts that fill with water can freeze and crack in cold weather.
- Check top-floor ceilings and the tops of walls after storms and hard freezes, which the same brief suggests as an early warning. A new stain right below a drain or gutter points to the drainage path; a stain elsewhere is often the roof surface or the flashing.
- Ask for photos after a rain. The roofing brief says that when the slope is inadequate or the drains clog, rainwater pools on the roof. Puddles that sit there tell you to ask whether the fix is clearing an outlet or correcting the slope.
The Park Service's moisture brief says a 2-inch-per-hour rain can push about 200 gallons through a house's downspouts in one hour, and a broken pipe sends that against your wall and foundation.
Shared roofs and neighbors
On a row, gutters, parapets and downspouts can be shared, and work on one roof can change where water goes on the next. Before signing a proposal that touches a shared gutter, a scupper or a neighbor's roof, ask which roof areas feed that outlet and whether the work changes where water goes. Agree with your neighbor in writing on access and who pays, and remember that moving your water onto their roof isn't legal.
Roof decks and green roofs
The manual says a roof deck needs zoning and building permits, its walking surface must let water reach the downspout, and that surface should come up easily so the drain under it can be checked for debris. On a green roof, keep soil and plants from building up around the drains.
Who to call, and what to ask
Call a roofer who works on low-slope roofs for ponding, a clogged scupper or gutter, or damage to the roof covering. Per the manual, leaks are fairly easy for a pro to find on modified bitumen and harder on EPDM rubber. The roofing brief recommends inspections at least twice a year; spring and fall make sense, since that's when gutters fill with leaves.
Call a licensed plumber when the problem is below the roof: a broken downspout, the boot, or the pipe in your basement. If a ceiling is sagging with water, stay out from under it and get a pro out right away rather than trying to drain it yourself.
Ask either one what's making the water stand or spill (debris, a crushed or undersized outlet, or the slope), whether the fix is clearing, repairing or moving a drain, and who pulls any permit.
Which drain work needs a Philadelphia permit
L&I's plumbing permit page says installing, altering, repairing or replacing plumbing needs a permit, but stopping leaks and clearing stoppages doesn't. So clearing a clogged roof drain or downspout needs no permit, while repairing or replacing a roof drain or storm drain does; on a one- or two-family home that fee was listed at $31 when we checked in October 2026. A licensed master plumber can apply as your agent. Per L&I's code bulletin B-2501, applications received on or after July 1, 2026, including trade permits, must meet the 2021 codes.
If the roof covering itself is being replaced, see our guide to roof replacement permits. If you'd like to hold some water on your lot instead of sending it all to the sewer, our stormwater credits guide covers the city's programs.