What is the Difference Between Floor Area and Lot Area?

Floor area and lot area are two terms commonly used in zoning analysis. While often used in combination to determine other areas or ratios – such as Floor Area Ratio (FAR), for example – the two have distinct differences and are defined differently by code.

A lot area is the total area of a property, including the yard up to the boundaries (property line), while the floor area is the area inside the building that is occupiable, up to and including the exterior walls. Floor areas can include spaces like bedrooms and living areas while lot areas are reserved for yards, driveways, walkways, balconies, decks, and porches that do not have a “solid” cover.

There are many factors that go into what is a floor area and a lot area, calculating these two areas, and what scenarios create different types of ratios. We’ll talk about all that below to make sure you understand everything there is to know between floor and lot areas.

What is Floor Area?

A floor area is an area, usually measured in square feet or square meters, that is taken up by a building or part of the building. Generally speaking, it’s the portions of a building that are deemed occupiable.

Defining floor areas can be tricky as there are different ways of measuring as well as opinions on what should count. Most zoning does not count spaces such as basements or garages as part of the floor area, although if it is fit for habitation and a certain height, it could be included as floor area.

A good way to think about it is to imagine a two-story house in the suburb. It has a couple of bedrooms and bathrooms, a garage, stairs, and living areas. Every part of the house that is deemed livable can be used in something called the FAR or Floor Area Ratio.

What is Lot Area?

A lot area is the area of the property up to the boundary. This is usually easier to measure, and most of the time is given to you by the zoning department in your city. In a suburb, a lot area is just the yard encompassing a house but in the city, a building’s lot area can include things like parking lots, garages, and land surrounding the building.

These lots are usually zoned by the local government. The government decides where they will zone things like residential areas, commercial buildings, and even agriculture or industrial buildings. This allows cities to understand which parts of the town they are able to grow and which parts are getting close to capacity.

More on Floor Areas

Floor areas have much more that goes into measuring and tracking them than lot areas. Because lot areas are determined by legally documented field surveys, it’s difficult to change them. But there are various ways to define floor area and the factors that influence the number.

In most situations, there can be three different levels of floor areas. The first one is the gross floor area, which is the total floor area measured around the external side of the external walls. The gross internal area is the area that goes from the inner side of the external walls.

Last is the net internal area, and this is what gets used most of the time. The net internal area is the gross internal area and then you subtract the things like stairs, basements, garages, and whatever else in the building that is deemed unlivable.

When it comes to taller buildings in cities and even hotels, the net internal area gets even more complicated. You can have a lot that is a certain size, but the building can be twenty stories high or higher.

In these types of buildings, areas like lobbies, elevators, and even places like mechanical rooms and columns to hold up the building are not deemed liveable, so they don’t count as floor area. This makes calculating the floor area ratio even trickier than your normal suburban house.

How to Calculate the Floor Area Ratio

The Floor Area Ratio is the total amount of usable floor area that a building may have. This can either be the space they have available currently or the amount they are permitted to by the developers.

You find the FAR by dividing the net internal area by the total lot area. For example, if you have a 3,000 square-foot lot and a 1,500 square-foot building that is all determined livable, then the Floor Area Ratio would be .5. If that same building had 500 square feet of stairs, garages, and other factors that get subtracted out, making it 1,000 square-feet, the Floor Area Ratio would be .33.

Which Should be Bigger: Lot Area or Floor Area?

In all the examples so far, the lot area is bigger than the floor area because suburban houses typically have lots that are larger than the building that is on that lot. This is especially true in rural areas where the size of the lot is significantly larger than the building.

But what about larger cities? Buildings that basically go to the property lines can be, however, as many stories high as they’re allowed to be. A ten-story building has ten times the square footage of a single-story building with the same area of each story.

Let’s take our example from earlier. There is a 3,000 square-foot lot with a building that has 1,000 square feet of a building internal area. This brought our FAR to .33. Now, if that building has 10 floors all with 1,000 square feet each, that’s 10,000 for the building internal area. This makes the FAR formula 10,000 divided by 3,000 which equals 3.33.

When it comes to rural buildings against urban buildings, this is usually the case. Most rural spots have lots of land with smaller buildings, and most urban places have a small amount of land and as much building as they can squeeze into it.

How Zoning Affects Floor Area Ratio

Most of the time, the local government has a limit on how much of a floor area ratio your building has relative to the lot around you. Every place is different in what they allow and don’t allow, but there are some general guidelines that can be followed.

If we’re talking residential or commercial, there are zones known for low density and high density. Low-density homes are what we mostly call houses. A building with one or two stories with a front yard, back yard, driveway, and other things outside the floor area. In low-density zones, you’ll mostly find the floor area ratio to be under 1 or close to 1 in big two-story houses.

High-density buildings are what we see in cities. Multiple floors with lots of different residences or businesses residing in the building and a floor area ratio that is usually a lot higher than 1.

Zoning regulations are determined by local governments. They’re the reason you don’t see single-family houses in the middle of Times Square in New York City or any other large city. These zones have different density requirements which directly correlates with their floor area.