Floor Area Ratio (FAR): What It Is, How to Calculate it, and Texas Exemptions

If you’re building a home, or if you’re a developer working on construction of a new building, you may have finally discovered your local floor area ratio (FAR) requirements. If you’ve never had to deal with these before, or never in your current market, it can feel like an unexpected setback. 

But rest assured, understanding and calculating FAR is not as complicated as it may first appear. It’s a very simple calculation, and you just need to be aware of local exemptions and requirements.

What is floor area ratio (FAR)?

Floor area ratio (FAR) is a measurement, expressed as a decimal, that describes the total amount of usable floor space in a building compared to the size of the lot that the building is on.

far equation

Note that the “gross building floor area” is not necessarily the same as the building’s footprint area. It may be close to the same for single-story buildings, but in multiple story buildings, the usable floor space of each floor is added together for the total building floor area.

Floor spaces that are not consistently used—like non-residential basements, elevator shafts, parking garages, stairwells, etc.—are generally not considered in FAR calculations.

Why is the floor-area ratio important?

Cities, towns, and municipalities will establish limitations and guidelines for buildings’ FAR in various neighborhoods, to maintain development standards and guide or restrict the development of local communities. 

Additionally, cities have a “safe load factor,” which represents the population density that can be safely maintained. FAR restrictions are one way that local governments maintain safe capacities.

In Austin, Texas, for example, the McMansion Ordinance requires a maximum FAR of “the larger of 0.4 to 1 (40%), or 2,300 square feet.”

How to calculate FAR

In general, the floor area ratio is calculated by dividing the total floor area by the total property area. Local laws, however, will vary in the details of what should or should not be included in those areas. Basements and attics, for example, may or may not need to be included in your floor area sum, so make sure you’re familiar with local regulations.

  1. Sum the usable floor area. On each level of the building (or proposed building) add up the usable floor space. This generally does not include basements, attics, stairwells, or elevators. Other exclusions may apply in your city. This is the gross floor area.

  2. Sum the property area. This is generally the area of the entire parcel, less any undevelopable areas like swamps, waterways, public walkways, etc.

  3. Divide the floor area by the property area. This is your floor area ratio.

Example: FAR Calculation

Let’s consider a hypothetical example (with small, round numbers, just to make it easy): a real estate developer wants to build a three-story residential building on an empty lot. The property has 400 feet of street frontage and is 600 feet deep. Each floor of the building—minus the elevator and stairwell—is 200 by 300 feet.

The usable floor area of each story is 60,000 square feet (200 x 300), which means the total usable floor area of the building is 180,000 square feet (60,000 sq ft x 3 stories).

The property area is 240,000 square feet (400 x 600).

The floor area ratio, then, is 0.75 (180,000 / 240,000).

Texas FAR Exemptions

If you’re building in Austin, or across the State of Texas, be sure to consider Texas’ list of exemptions—or spaces that do not need to be considered as parcel or floor area size.

FAR Exemptions for Parking

You can take advantage of a number of exemptions regarding parking facilities. For instance, deduct 450 sq ft if your building’s parking structure is:

  • A rear structure, 10 ft away from the building’s primary structure.
  • Detached (excluding an open breezeway) and 10 ft away from the building’s primary structure. 
  • Designed with more than two open sides and does not include any habitable spaces above it

Deduct 200 sq ft if:

  • The parking area is attached to the building but meets the minimum requirements of parking.
  • The parking area is a detached structure located within the proximity of the primary structure.
  • The parking area is within 10 feet of the primary structure and is close to a breezeway.

Getting both exemptions for your building’s parking area is also possible.

FAR Exemptions for Attics, Basements, and Porches

It might sound surprising, but FAR regulations in Texas exempt some porches, basements, and attics. 

For example, the ground-floor porch is exempt if it is not attached to any driveway or not accessible by the vehicles. 

FAR may exempt habitable basements if they;

  • Stick to the first-story footprint.
  • Are located below the finished grade.
  • Have 50 percent perimeter walls in surroundings.

All habitable attics are exempt if:

  • The roof has a 3 to 12 inches slope.
  • The building has one floor.

Floor Area Ratio

FAR regulations often creep up as an unexpected complication in designing a house or other property for construction. A local architect, however, will not be surprised by the requirements, so make sure you’re working with an experienced professional.

And once you understand what the FAR is, why it’s important, and how to calculate it, you see how small a hurdle it usually is. Your first step to calculating the FAR is to make sure you understand all of your local government’s requirements and exemptions.

As you get ready to kick off a building project in Texas, be sure to also investigate how hard money construction financing can help you get the job done with fewer delays and less red tape.

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