Roofing in Washington usually means the roof of a District rowhouse, hidden behind a parapet, often low-slope, often tied to a rear ell that was built as part of the original plan and has been leaking at the joint ever since. You will not diagnose it from the front stoop. Harbor is the wrong river. This is Potomac and Anacostia damp, sitting on a membrane or an old built-up surface that ponds when a scupper clogs.
The ell joint and the party-wall flashing are where these calls begin. Water runs along brick, drops three rooms from the hole, and looks like a pipe until someone is above the ceiling. Ice is occasional, not the main event. A summer downpour that sits on a flat roof is the main event. Tell us if the stain grows only after water has had time to pond, or if wind drives it in at a parapet cap. Those are different repairs.
Access is a hatch, a rear window, and an alley. Debris does not leave through a wide drive. Chimneys and old parapet caps crack. Coatings piled on a tired surface are common and worth mentioning. If the neighbor shares the stain, the party wall may be the source. Do not walk a wet membrane to prove the point. Say pitched front, flat main roof, ell, or some combination, because many of these houses are a combination.
Inside, note the floor, whether the spot is near an outside wall, and whether a bath above could be confusing the picture. A cockloft that smells damp is a fact. Shaded ell roofs stay wet longer than the street side. Leaves and seed pods pack the scupper and then the ceiling pays for it. If a claim is also in your head, describe the leak before the paperwork.
Say repair or replacement. Roofing in Washington is parapets, scuppers, ells, and party walls on District rowhouses that take humid storms. Call the number on this page.