Replacing a Roof on a Trenton Rowhouse or Twin: What the Shared Wall Changes

What does a rowhouse or twin replacement involve from start to finish?

Preparation, access, tear-off, deck repair, new membrane or shingles, party-wall and parapet detailing, flashing at chimneys and vents, and cleanup. On an attached house each stage involves the neighbor's wall in some way, so the schedule and the detailing differ from a detached job. The sequence below sets out the usual order.

Row houses in Chambersburg, North Trenton, the East Ward and the older blocks of Burlington, Bristol and Morrisville share long runs of brick wall. A roofer working on one is working on a shared boundary, even if the roof surface is theirs alone.

The table gives a plain timeline of what happens and when to raise each question. None of it requires technical knowledge, only a willingness to ask the roofer to explain.

How is the party wall detailed so water cannot cross it?

The roofing is turned up the wall and sealed under metal flashing, with the top edge set into the brick or covered by a cap. On a parapet, the cap keeps water out of the masonry. The metal must lap the roofing so water runs over each piece. Sealant alone is not a lasting detail.

Think of it as a shallow tray. The roof is the floor of the tray and the party wall is its edge. If the edge is not sealed and capped, rain that runs down the wall or blows against it finds the gap.

Ask the roofer to show you or photograph the detail before it is covered. See roof flashing repair for how step flashing and counter-flashing work together, and rowhouse and twin roofing for the wider job.

What if my neighbor's roof is older than mine?

Water can reach the shared wall from the older roof and show up inside your house even after yours is new. You cannot make a neighbor repair their roof, but you can detail your side carefully, record the condition of the joint and tell the neighbor what you find. A calm, factual conversation usually works best.

Row house roofs are often replaced at different times by different owners. A new roof next to an old one looks tidy until the old one starts to leak at the shared wall. Then the question of whose roof is at fault arises.

Take dated photographs of the joint before the work starts and again when it is finished. They show what you did and what you found. If the neighbor's side is plainly failing, the roofer's written findings give you a neutral document to share, and a neighbor who sees it may choose to act.

If water keeps entering, talk to the roofer about extra protection on your side, such as a deeper turn-up or a cap. Do not try to repair next door's roof without permission.

Why is a flat section not just a cheaper shingle roof?

Because shingles need slope to shed water, and a flat or nearly flat section has too little. It needs a continuous membrane, sealed seams, drains and detailed edges. The materials, labor and skills differ from shingle work, and the price is set on its own line, often with its own roofer's expertise.

Many rowhouses have a pitched front and a flat back. The two parts are separate systems that meet at a joint, and that joint is a place to look carefully. A roofer who quotes only for shingles, or who proposes shingles on the flat part, has not understood the house.

The guide on flat roofs on rowhouses and twins explains the membrane choices and why ponding matters. The flat and low-slope roofing page covers repairs.

How do access and the street change the job?

Narrow frontage, parked cars, shared passages and tall rear walls limit where ladders, lifts and dumpsters can go. Debris may have to come down a chute or through the building. Ask the roofer for a plain plan for materials, debris and parking, and for how the neighbors will be kept informed and protected.

On a busy block, a dumpster in the street may need a permit from the city, and parking may need to be arranged in advance. Ask the roofer who handles that and whether it is in the price.

Interior protection matters too. Hammering shakes plaster, and dust falls in the attic. Cover or move things from the top floor, and ask the roofer how they will protect the stairwell.

Weather planning is part of access, too. A row house roof is small enough to be stripped and closed in within a day or two, but only if the forecast cooperates. Ask the roofer what the plan is if rain arrives while the deck is open, how the opening will be covered overnight and who to call if water shows up inside before the new roof is finished. A crew that has a plain answer to that has done it before.

What if the work damages my neighbor's property?

Ask the roofer before the job how damage to next door would be handled, and ask for proof of current insurance in the contractor's name. Photograph the neighbor's wall, roof edge and any shared passage before work starts, with their agreement. Report any damage at once, in writing, to the roofer.

Most jobs finish without incident, but a ladder against a shared wall, a dropped tool or a heavy rain on an open roof can affect the house next door. Settling how it would be handled in advance is far easier than arguing about it afterward.

A short note to the neighbor with the roofer's name, the dates and a phone number lets them raise concerns early. If the neighbor wants to be present when the party wall is opened or capped, say so to the roofer so the visit can be arranged.

Insurance questions go to your insurer, and nobody on this line can say what a policy covers. Ask the roofer to give you a current certificate of insurance and read what it says before work begins.

What about permits, historic review and the contract?

Expect a permit on an attached home, since published summaries of New Jersey's rule say attached homes do not qualify as ordinary maintenance. Mill Hill may add review by the Historic Preservation Commission. The contract should carry the roofer's registration number, a written scope, the price and the dates, and be signed by both sides.

Confirm everything with the municipal construction office, which has the last word. The guide on roofing permits in Trenton and Mercer County goes through the pattern, and how to check a roofer in New Jersey explains the registration and contract points.

On the Pennsylvania side, in Bristol or Morrisville, the registration is with the Attorney General and the permit rules are the borough's. See hiring a roofer on the Pennsylvania side.

How do I keep the record straight for the next owner?

Keep the signed contract, the permit and inspection record, the roofer's written scope, photographs of the deck and the party-wall joint, and any workmanship terms in the quote. A tidy file helps with insurance questions, with a sale and with the next roofer, who will want to know what is under the surface.

Attached houses change hands often, and a buyer's attorney may ask for roof paperwork. A folder with the permit and the photographs answers most of the questions before they are asked.

Write on the file the roofer's name, registration number and the date of the job, and note anything you agreed about the shared wall with your neighbor.