Michael Stern

By Michael Stern, JDS Development Group Somewhere above the occupied floors of a very slender tower there is a level with no walls and no glass, open to the air on all four sides. From the sidewalk it reads as a gap in the building, a band of shadow where the windows stop and then start again. It is there because of what moving air does to a tall narrow prism, and it is one of the few places in a tower where the shape of the building and the behavior of the wind are a single decision. This is written for architects, structural engineers and developers looking at a footprint that is too small for the height they want. The question underneath it is how much of a tall building has to be given up to the air before the rest of it will hold still. How Wind Sheds Vortices Off a Tall Tower Air arriving at a tall building does not flow smoothly around it. It separates at the corners and rolls off each face in turn, first one side and then the other, in a rhythm rather than a steady push. That ...

By Michael Stern, JDS Development Group The building standing at the edge of my excavation has been there for a century and is not permitted to move. That one condition governs how deep the cut goes, the order in which soil leaves the site, and the shape of the foundation that eventually replaces it. This is written for developers, geotechnical and structural engineers, and construction managers who are about to open the ground beside something that is protected. Most foundation work is designed forward. You know the building you want, you know what it will weigh, and you work down to something that will hold it. Beside a designated structure the sequence runs the other way, and the drawing set reads differently because of it. What a Landmark Can Tolerate Sets the Design The first quantity that matters on a site like this belongs to the old building rather than to the new one. Old masonry has a limited appetite for movement, and it has a different appetite for each kind. Vertical...

By Michael Stern, JDS Development Group Photo by Wojciech Wyszkowski on Unsplash A zoning district boundary does not stop at a property line. It is drawn on a map at the scale of a neighborhood, and now and then it runs straight through the middle of a single lot, leaving one piece of ground answering to two sets of rules at once. If you develop on constrained urban sites, or you advise the people who do, the split lot is the condition that most often explains why a building on an ordinary looking site came out in an unusual shape. What follows is how that works, in order, because the order is the whole insight. The floor area on such a lot is not computed once. It is computed for each portion, under the rules of the district that portion sits in, and the building is the sum of what those two computations permit. How Floor Area Is Computed on a Split Zoning Lot Start from the ground. The lot is one parcel in the deed and two parcels in the zoning, and the line between them i...

By Michael Stern, JDS Development Group A second structural engineer opens the calculations of the first and works the problem again from the beginning. On a tower whose behavior no code table describes, that duplicated effort is bought on purpose, and it belongs inside the design schedule rather than at the end of it. This is written for developers, engineers of record and construction managers about to take on a site where the ordinary references stop being useful. What Structural Peer Review Actually Is Peer review is an independent structural engineer, retained separately from the design team, reading the load path, the analysis assumptions and the calculations that sit behind a design. The reviewer does not take over the design and does not become the engineer of record. The reviewer reads what the team produced and says where the reasoning does not hold. On a conventional building the code has already done most of that work. Wind loads come from a published standard, the fr...

By Michael Stern, JDS Development Group A foundation is completed on a Thursday and the zoning that governs the site changes the following week. The building that foundation was designed for is still legal. The building the new text describes is a different one, and nobody is building it on this lot. This is for developers, land use lawyers and construction managers working on sites where the rules move while the schedule runs. The mechanism that decides the outcome is a recognition, written into zoning itself, of work that has already substantially begun. What it protects is progress in the ground, and what it turns on is a very small number of dates. What Zoning Protects When Construction Has Already Begun A zoning amendment does not reach backward through every project on every lot. Text and maps change constantly, which is ordinary work in the planning profession and a standing condition for anyone developing on a long timeline. A project that has reached a defined stage of ...

By Michael Stern, JDS Development Group Photo by Bekky Bekks on Unsplash 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 agai...

By Michael Stern, JDS Development Group Photo by Parsoa Khorsand on Unsplash An owner of a five story building on a good block asks what it would take to add three floors, and the answer comes back from the title report rather than from the zoning map. The lot still has a district, a permitted floor area, and a shape. What it no longer has is the unused area that once sat above the roof, because that area was sent to a neighboring lot years ago and it is not coming back. This is written for developers looking at assemblage, for land use lawyers who field the same question from the other direction, and for owners of small buildings who assume the room above them is still an asset they hold. The mechanism is ordinary. The consequence is permanent, and that combination is rare enough in this business to be worth understanding before anyone signs anything. How Floor Area Leaves a Lot Permanently Unused floor area is an arithmetic difference. It is what the zoning permits on a lot les...

By Michael Stern, JDS Development Group Photo by camera obscura on Unsplash A lot on an assembled site can carry floor area that no survey of that lot will ever show. The area arrived from a neighbor, it lives in an instrument filed with the office that keeps the land records, and the only place it can be proved is the record of title. This is written for developers, land use lawyers and underwriting professionals who have to establish how much building a site actually holds before a design exists. On the sites I work on the buildable envelope is assembled rather than found, and the assembly is legal before it is physical. The document that performs it is a recorded declaration, and everything the tower is permitted to be rests on that document being drafted and filed correctly. What a Development Rights Transfer Actually Records A transfer of unused floor area is not a conveyance of land. Nothing about the boundary of either lot changes and both owners keep their parcels. ...

By Michael Stern, JDS Development Group Photo by Sebastian Hages on Unsplash Two lots on the same block each hold floor area they will never use, and a third lot sits between them. That third lot decides whether either of the first two can ever contribute to a tower, because under the general rule floor area moves only between lots that form a single zoning lot, and a zoning lot has to be contiguous. This is written for developers and land use professionals evaluating an assemblage, and for anyone who has looked at a block map and wondered why a small site can hold a tall building while a larger one nearby cannot. What a zoning lot is and why it is the unit that matters Floor area is counted on the zoning lot , a unit the zoning creates for its own purposes, which can be one tax lot or several tax lots treated as one under the rules. The deed map and the zoning map therefore disagree by design. The deed map shows who owns what, the zoning map shows what may be built where, and the...