When the Building Code Is Tighter Than the Zoning

By Michael Stern, JDS Development Group

The building code carries a table that sets how tall a building may be and how large its floors may be for each type of construction it allows. Read that table beside the zoning for a site and the smaller number is often the code one, which means the top of the building was decided by a construction document rather than by the envelope rules. I am writing this for developers and architects working on constrained sites in the middling heights, where the two documents disagree and only one of them can be satisfied last.

What the Height and Area Tables Actually Govern

The code sorts buildings by what they are made of and how well that material is protected from fire. Each type carries a permitted height and a permitted floor area per story, and the use of the building moves those numbers again. Nothing in that table is about light, air, bulk or the street, which is the whole business of the model codes a body like the International Code Council publishes standing apart from the zoning.

A site therefore has two ceilings. The zoning gives an envelope, meaning a shape the building may occupy and a quantity of floor area it may contain, and in New York that envelope comes from the 1961 Zoning Resolution and everything written into it since. The code gives a limit on height and on area for each construction type the building might be built as, and the finished building has to answer both.

What I can describe is the mechanism and not the figures. The thresholds, the construction types and what each one requires are set by the code in force and move between editions, exactly as the quantities in the current zoning text do, so the architect of record and a code consultant read both for the specific building.

The area limit is the one that gets forgotten. A construction type caps the floor area allowed on each story, so a site can clear the height question and still find that the plate it wanted is larger than its type permits. The answer there is a different type or a smaller plate, and both are structural decisions.

Why Crossing a Height Threshold Changes the Whole Building

A threshold is not a line you pay a fee to step over. Above it the code wants a different construction type, which usually means noncombustible structure carrying a heavier rating on the columns, the floors and the shafts. That rating is a property of the whole building and not of the floors that caused it.

The requirement then carries into everything the building has to do at that height. Stairs become more protected and sometimes more numerous, shafts are enclosed to a higher standard, the sprinkler and standpipe design changes, and smoke control arrives as a system rather than as a detail, along the lines that the fire protection standards kept by the National Fire Protection Association describe.

Every one of those changes has a schedule attached to it. Fireproofing is a trade with its own sequence, a second stair takes usable area away on every floor it serves, and the systems that come with the higher rating want coordination before the structure is drawn rather than after.

On the floor the rating shows up as thickness. Sprayed or boarded protection adds dimension to every column and beam it covers, which takes from the ceiling height and from the space the ducts and the sprinkler mains were going to share. A building that picks up a heavier rating late loses that coordination twice, once on paper and once in the field.

How a Massing Study Should Be Read Against the Code

A massing study arrives from the zoning side, drawn under whichever zoning is in force when the work begins. It shows the envelope, the setbacks and the area the site can hold, and it is usually the first picture anyone on the project has of the building.

The useful second step is to ask a code consultant what construction type that massing implies and what the next threshold above it would ask for. On a site of middling height the answer often lands a few floors below the top of the envelope, and a project that files toward the Department of Buildings without having asked is designing upward into a wall it has not drawn.

The two studies are not one document and they are rarely done by the same people. A zoning consultant answers what the site may hold and a code consultant answers what the building may be, and a project needs both answers before it believes a massing. Running them together is cheap and running them in sequence is how a scheme gets drawn twice.

A code consultant will also tell you which thresholds are near rather than crossed. A scheme sitting one floor under a limit has no room left for a later change.

Doing it in that order costs a week. Doing it after the design is developed costs the design, because the structure, the stairs and the mechanical plan all move together the moment the construction type moves.

What the Threshold Costs a Site

A competent engineer could read all of this the other way and say the threshold is a price rather than a ceiling, and that a building which wants those floors should buy the heavier construction and take them. On a tall enough building that is plainly correct. 111 West 57th Street is the tallest and most slender residential building in the Western Hemisphere, and a building at that height settles its construction type once, at the start, and never asks the question again.

Where I think the argument fails is in the middle of the range, on a site whose envelope offers two or three floors above a threshold.

Those floors arrive with a heavier structure running through everything beneath them, which is a cost the bottom of the building carries so that the top can exist.

So we leave floors unbuilt, and I no longer treat it as a failure of the analysis. It is a compromise accepted rather than solved, and it survives in the file as a drawing of an envelope with a line across it where the code stops.

Some sites take the floors anyway, and on a plate large enough to spread the heavier structure across many apartments that can be the right call. I have built on enough narrow ground to be skeptical of it, because a narrow plate has fewer rooms to carry the cost. The engineer who disagrees with me is usually working on wider ground than the sites I take.

Retain a code consultant beside the architect of record at the same hour you commission the zoning analysis, and hand them the same massing. An envelope is an offer. The code is what the building has to become in order to accept it, and on many sites that answer arrives a few floors down.

Michael Stern is the founder and chief executive officer of JDS Development Group.