Porch roof repair in Washington, DC

Thousands of rowhouses built from the 1910s through the 1930s in Petworth, Brookland, Trinidad and Bloomingdale have a full-width front porch with its own small roof. That roof is separate from the main roof above it. It has its own membrane, its own drainage and its own edge details, and it ages on its own schedule.

Most porch roofs are nearly flat, pitched just enough to push water toward the front edge. Over the years they've been covered with rolled roofing, built-up tar and gravel, modified bitumen or old soldered tin painted silver. They sit low, catch every leaf that blows down the block and get walked on by anyone painting the second-floor windows.

They're also easy to ignore. You can't see the porch roof surface from the sidewalk, and the main roof usually gets all the attention when a house changes hands. We often find a porch roof two or three layers deep, with the newest layer laid right over a rusted tin pan that's still trapping water underneath.

The back edge of a porch roof butts into the front wall of the house, right under the second-floor windows. Water running down the brick and off the window sills lands on that joint in every storm. If the flashing there fails, water gets behind the membrane and runs straight into the porch ceiling and the ledger board that carries the roof.

A proper repair uses two pieces. A base flashing turns the membrane up the wall at least eight inches, and a metal counterflashing is set into a ground slot in a mortar joint and folded down over it. What we usually find is a strip of roofing cement smeared along the brick, cracked open in a dozen places.

We also look above the joint. Open mortar joints, a cracked window sill or a failed caulk line around the window frame can put just as much water behind the flashing. If the brick needs repointing along the flashing line, we do that before the new metal goes in so the counterflashing has solid mortar to hold.

Porch ceilings on these houses are usually tongue-and-groove beadboard nailed to the underside of the roof joists. When it stains, buckles or drops at one end, the roof above has been leaking for a while. We pull down the damaged boards to see the joists and the deck boards before quoting, because a ceiling stain can hide rot that runs several feet back.

The front fascia board takes the worst of it near the gutter outlet, where all the water from the porch roof leaves through one opening. We replace rotted fascia with primed wood or PVC milled to the original profile, and we save and reinstall sound beadboard whenever we can. Our fascia and soffit work covers deeper trim repairs on the rest of the house.

Square wood columns and their capitals often rot at the top, where water drips from a failing gutter. If a column has gone soft, we shore the porch roof with temporary posts, replace or rebuild the column, and set it on a raised base so it doesn't wick water from the porch floor.

Many porch roofs end in a small built-in gutter formed into the front edge, lined with tin or copper and drained by one outlet into a downspout at the end of the porch. When that lining rusts, water drops into the fascia and the column tops. A relined trough is the same kind of work as our box gutter repair, just on a smaller scale.

On blocks in Trinidad, Bloomingdale and Petworth, porch roofs often run continuously across two or more houses with no break at the property line. Water from your neighbor's porch can cross onto yours, and a failed seam at the line can leak into both houses. We talk with the neighbor before any work on a shared roof, and we tie the new membrane into theirs with a sealed lap so neither porch is left exposed.

A repair makes sense when the membrane is fairly sound and the trouble sits in one or two places: the wall joint, a seam, the gutter outlet or a puncture from a ladder. We cut out the bad area, dry and fix the deck underneath, patch in new membrane and reflash the wall.

Replacement is the better call when the roof has more than one layer, the deck boards are soft in several spots or the old tin pan is rusted through under the newer coverings. We tear off down to the joists, replace rotted decking with plywood or new plank, and install a two-ply modified bitumen or a single-ply membrane with new wall flashing, drip edge and gutter lining.

A porch roof replacement on a rowhouse generally needs a DC Department of Buildings permit. If your house is in a historic district such as LeDroit Park, Shaw or Capitol Hill, changes visible from the street, like a new gutter profile or column design, go through the Historic Preservation Office. Call (202) 771-7443 and we'll look at the porch and tell you which route fits.