Understanding Gross Floor Area

IP Applied Research Lead, Murray Blore dives into the complexities of local authority compliance reporting of floor areas.

October 19, 2022
Durban, South Africa

Imagine trying to write something interesting about Gross Floor Area?!

It’s an important topic, and it really should matter to most building owners (that is, our clients), considering how often it is used to determine tariffs or fines by various local authorities.

In New York City, for example, whether or not your building complies with the new Local Law 97, is determined by multiplying the building’s “Gross Floor Area” with an allowable greenhouse gas emissions coefficient.

The question is, how do we all describe the “gross building area” in the same way, so that when we compare them against some standard or regulation, we know that we’re comparing apples with apples.

Should you measure to the inside face of the external walls or to  the external face? Include staircases on every level? Include vertical shafts (even though there’s an opening in the slab), but don’t include the voids in atriums (where there’s also an opening in the floor slab). 

If only we had a standard that we all used so that we know we’re talking the same language.

And don’t get excited. No, we don’t have one. Well, actually, we have quite a few, and therein lies the perennial problem: which standard should be the standard standard?

For New York City, I found 2 conflicting definitions in the Rules of the city and the City’s building code. The city literally contradicts itself!? (Disclaimer: More likely is that there’s something I don't understand about which rule to use, but that just highlights the complexity of the problem.

In New York City,

Gross Floor Area means: 

“the total number of square feet measured between the exterior surfaces of the enclosing fixed walls. “

As defined in The Rules of New York, (Section 103-06 of Title 1) regarding the annual reporting of energy and water use (Local Law 33)

gross floor area
Gross Floor Area

In New York City,

Floor Area, Gross means: 

“The floor area within the inside perimeter of the exterior walls of the building under consideration,”

That’s the 2022 NYC Construction Codes: Building Code: Chapter 2: Definitions

Floor Area, Gross

If I measure our BIMIT sample model according to each standard, that ends up with a 260 SF difference in area, over +/- 4000 SF. That’s significant, and it could potentially tip your building into non-compliance or compliance of a certain law (like LL97 if you're in NYC) via a trick of math.

Global Standards?

It’s not actually overly complicated. 

In fact, those 2 measures used in NYC are the same those described by The International Property Measurement Standards Coalition (https://ipmsc.org/) as IPMS1 and IPMS2, or Gross External Area and Gross Internal Area, instead of just as Gross Floor Area.

From there, either gross floor area measure seeks to simplify the measurement of building area as much as it can. So, everything inside of the external perimeter walls (including stairs, elevator shafts, or mechanical plant rooms) gets included, with the sole exception of unroofed courtyards.

It’s only a matter of deciding whether to measure to the internal or the external wall face.

IPMS1 or Gross External Area  source:  https://ipmsc.org/standards/office/

You can make things a lot more complicated when thinking about leasing areas and dividing usable space for service areas and common area from exclusive use space, but those questions are for tenant management, not local authorities.

At Integrated Projects, we’re working to align our area reporting methods with those required by local authorities both in NYC and around the world, allowing our users to confidently include IP Verified areas into their compliance reporting.

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