Party Wall Rights Fix the Edge of a New Building
By Michael Stern, JDS Development Group
On most assembled sites in New York City there is a masonry wall standing directly on a lot line, shared by two buildings that were never designed together. It is the oldest structure on the property and it is usually the only one still standing when the new building opens. This is for the developers, architects and structural engineers who are looking at a site like that and working out how much of it they actually control.
A party wall is inherited structure. Everything the new building does along that edge gets arranged around masonry that was built for another purpose, by people who are gone, to a standard nobody wrote down.
A Party Wall Straddles the Lot Line
A party wall sits astride the boundary rather than beside it, with part of its thickness on each lot. Both buildings bear on it, which is what distinguishes it from a wall that merely stands close to the line. Two independent walls built tight against each other look identical from the sidewalk and behave completely differently once the dig starts.
Telling the two conditions apart is survey work and record work together. Old drawings help where they survive, the thickness of the wall is suggestive, and pockets cut into the masonry for the floor joists of the building on the other side are the clearest evidence of all. On an assembled site this question gets answered before anything else, because everything downstream of it changes with the answer.
Where lots touch, what crosses the boundary matters as much as the floor area that moves across it, and floor area moves only between lots that touch. The wall is the physical form of that same adjacency. It cannot be treated as site inventory to be cleared, because half of it is holding up something else.
Party Wall Rights Are Recorded and Run With the Land
The right that matters here is the right of support. Each building may rely on the wall to carry it, and that right attaches to the land rather than to whoever holds the land at the moment, so it survives every future conveyance. It arrives either through an instrument recorded in the city register of property records or through a condition that the law has long recognized on walls of this kind.
Reading the record is work for a real estate attorney with a title company, and it belongs at the front of a project rather than in the middle of one. What the record describes and what the wall is doing are two separate questions. I have yet to see a site where the second question was answered by a document.
The right of support is also narrower than people expect. It permits each building to keep leaning on the wall as it always has. It does not by itself permit the new building to load the wall further, to cut into it, or to take the top of it off, and each of those is governed by what the record says and by what the masonry will actually take.
The Wall Decides the Dig and the First Bay
Support of Excavation Along the Line
Excavating beside a party wall means removing the soil that is currently holding up the bottom of it. The support of excavation along that line is designed to keep the wall exactly where it is, using a system installed in sequence so the ground is never left unsupported over a long stretch at once. Its reach, the room it needs and the order it goes in are settled before the first machine arrives, and the work is filed and inspected like any other structural work under the city buildings department.
This is slow, and it is slow by design. The edge of the site proceeds in short lengths, each one supported before the next is opened, which is why that edge takes longer than the middle of the lot ever does. The geotechnical engineer and the structural engineer set the sequence between them, and bodies such as the Deep Foundations Institute are where the practice behind it is published and argued.
Where the New Columns Land
Above grade the same logic sets the column line. The new frame generally stands clear of the party wall on its own columns, so the new building carries itself and the old wall goes on carrying only what it always carried. That decision costs the first bay some depth, and on a narrow lot the first bay is a real share of the floor.
Everything else along that edge follows from the column line. The slab edge, the waterproofing, the fire separation and the detail where new floors pass the old masonry all get drawn to it, and they get drawn early, because moving that line later moves every one of them.
Height is the one place the wall lets go. Above the roofline of the building on the other side the new building is free of it, so the party wall governs the base and the bays beside it while the tower above answers to the envelope rules instead. On a slender building that division shows up in the plan as one edge that behaves differently from the other three for the first several floors.
111 West 57th Street rose in the courtyard of the landmarked Steinway Hall, and the discipline a site like that teaches is to dimension the new frame off what is already standing, in the order the existing structure permits.
A party wall is the one part of an assembled site that was designed by someone else and cannot be redesigned by you.
Why I Design As Though the Wall Always Stays
My working position is that the wall stays, and I hold to it even when the record suggests there may be a way to take it down. Designing for removal and learning late that the masonry has to remain is a rework of the foundation, the frame and the facade at the same time. Designing for retention and learning late that removal was available costs the first bay and nothing else.
A competent engineer can argue the other side of that, and plenty would. Carrying an old wall along one edge complicates waterproofing for the life of the building, forces details nobody enjoys drawing, and gives up usable area permanently in exchange for avoiding a risk that may never have been real. On a small lot that area is not a rounding error, and the case for testing the question early is a serious one.
The honest limit is that the condition of a party wall is not knowable from outside it. Mortar, thickness, what bears on it and what was cut into it over a century are found by opening it up, and opening it up generally happens after the design is fixed. Every project along a party wall carries some version of that gap between the drawings and the masonry.
The people who close the gap are a real estate attorney for the recorded rights, a structural engineer for capacity and connections, and a geotechnical engineer for the ground under the wall. Professional bodies such as the Structural Engineering Institute publish the standards that work gets measured against. What a developer owes the project is to have all three engaged before the first drawing assumes anything about that edge.
A wall that two buildings have leaned on for a century has already decided part of the site. The work is finding out which part, before the drawings quietly assume otherwise.
Michael Stern is the founder and chief executive officer of JDS Development Group.
