--

--

Broadly, there are four sets of costs: Air, Box, Transport, Setting

Air

This is the legal right to build on a rooftop. The cost is $0 if you already own the building and the air rights above. Otherwise, the cost fluctuates wildly depending on the code restrictions (including height and setback) overlaid on the neighborhood.

As for which particular air-rights (sometimes called development rights) may be used to construct a penthouse, NYC rules are complicated. Buildings are limited in terms of Floor to Air ratios (FARs). A typical FAR is 6.5, meaning floors may occupy 6.5 times the lots size. This converts into a six floor building covering the entire lot space, with half the roof available for contruction. Or, a 13 floor building that only covers half the lot. Or something in-between. Further restrictions include inflexible limits on height, and the visibility of new construction from the street. Every building and neighborhood is unique and will have to be evaluated individually. Restrictions tend to diminish as distance from Manhattan increases.

To set a number here, air rights may go for $100 per square foot. A 2400 foot home would cost $24,000 for the rooftop land.

Box

Building the home in the factory runs from $100 to $300 per square foot. One reason for the wide spread is that some manufacturers do more in-factory than others, resulting in higher-priced boxes, but lower on-site expenses. Cost also depends on construction materials selected, and finishings.

Between 75% and 95% of the home is constructed in-factory. This stage keys most cost savings. Built in a controlled and comfortable environment, these wood-framed modulars are solidly and more perfectly assembled than outdoor projects. At the $150 per square foot cost level, they’re finished with materials such as Anderson windows, cedar siding, EPDM rubber roofing membrane, hydro-air heating/AC system, bamboo flooring, Insteon dimmers, Halo recessed lighting, Merillat kitchen cabinets and vanities, Corian counters, all tile bathrooms, Kohler, HansGrohe, Duravit fixtures.

A 2400 square foot home—3 bedrooms and 2 bathrooms—constructed by Hive Modulars runs about $360,000 See a few examples here. At the high end, the Skyline series from Marmol Radziner runs about $300 per square foot, totaling $720,000. Examples here.

The price of these modulars which are built at low-cost sites including Scranton PA and eastern Long Island are so far inferior to Manhattan construction pricing that comparison verges on the absurd.

Transport

The home must be transported from the factory to NYC. Shipping costs between $5 and $32 per mile. Some of our modulars are constructed just outside the city, others as far away as Los Angeles (2400 miles). Shipping, in other words, runs from about $1,500 to $76,800.

Setting
Modules are set on the rooftop by a set crew and crane operator. A local general contractor team finishes the house on site. The set crew + crane + on-site hook-up and wrap-up costs add up to about $150 per square foot.

Extra costs accrue in three areas of local infrastructure: extending the elevator to the rooftop, preparing the rooftop to support the modules’ weight, and complying with code requirements for exit, fire safety and similar.

Excluding the extremely variable local infrastructure expenses, the setting cost for a 2400 square foot home amounts to $360,000.

Total Cost
With some exclusions and many approximations, the price on a 2400 square foot home with two bathrooms and three bedrooms runs:

$24,000 + $500,000 + $20,000 + $360,000 + building infrastructure = $904,000 + building infrastructure.

Finally, anyone who's worked in construction and renovation knows that no matter how far down into the details you plan, the project always costs 50% more than projected. Total cost, consequently and realistically, comes in around 1.35 million + building infrastructure.

The cost of a typical purchased PH of about 2400 sq/ft in the more desirable areas of New York City costs, according to Streeteasy (see listings here) somewhere between $2000 and $5000 per square foot. In other words, between: $4.8 and $12 million.