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Gross vs. net sq footage

PostPosted: Wed Jun 27, 2018 3:56 pm
by Nat
Hi all I have a quick question.
The definition of Net floor area as per the IBC is "The actual occupied area not including unoccupied accessory areas such as corridors, stairways, ramps, toilet rooms, mechanical rooms and closets."
Would a Lobby or Vestibule be considered Net or Gross?
Thank you

Re: Gross vs. net sq footage

PostPosted: Mon Sep 10, 2018 5:46 pm
by schwein
The way I always look at it, anything that is programmed space, ie, class rooms, offices, bathrooms etc.. are gross sf and this does not include spaces that support these spaces or things that are required by code, like hallways, mechanical rooms, and vestibules.

anyone else have an opinion?

Re: Gross vs. net sq footage

PostPosted: Wed Sep 12, 2018 8:45 pm
by MWilliams
I've overseen a lot of programming for many building types. Below are some of my shortcuts. The book Problem Seeking by Pena and Parshall is a great resource for programming standards. It has a whole section of efficiency/net to gross.

Net area is also called "net assignable". Space that can be assigned to someone for a particular use.

A lobby, beyond the "phantom corridor" required for egress, is net. Foyers and vestibules are gross.

I've found that a good starting point for estimating building efficiency is 80% x 80%= 64%.
Most utilitarian buildings are 60%-65% efficient. Warehouses much higher, courthouses much lower (less than 50%).

Here's how the 80% x 80% works:

Base building: about 80% available for floor layouts.
(the other 20% is structure, walls, mechanical spaces, building storage, shafts, elevators, egress stairs, public toilets, janitorial, etc)

Floor layouts: about 80% assignable.
(other 20% is interior corridors and partitions. (three lineal feet of partitions take up one SF)

hope this is helpful.