How Big Can Our Building Be?

One of the first questions clients ask is, “How big can our building be?” The answer depends on a few important factors, most of which come from the site itself.

The first step is to have a site survey completed by a licensed surveyor. This survey will establish the boundaries of your lot, the topography, and any easements that may limit what can be built. Paired with a quick search of the Property Valuation Administrator (PVA), this information helps us understand the zoning regulations that govern your property.

Primary or Accessory Structure

We need to define whether you're considering a Primary Structure or an Accessory Structure. The primary structure would be your main house or an addition to your main house. It's anything that attached to your home. The Secondary structure would be any building that doesn't attached to the primary structure. This could be a shed, garage, or ADU.

Lexington Kentucky

For residential projects in Lexington and Fayette County, lots are zoned from R-1A through R-5. Each zoning category has specific guidelines, and following them closely is essential to a successful project. One of the main tools used here is the Floor Area Ratio (F.A.R.), which measures the maximum building area allowed on a lot.

Here’s how it works: (Examples only: Check with zoning before starting any project)

• If your lot frontage is under 50 feet wide, the F.A.R. is typically .35 (35%).
• If your lot frontage is 50 feet wide or greater, the F.A.R. increases to .70 (70%).

The formula is straightforward: Gross Building Area ÷ Lot Area = F.A.R.

For example, if you have a 6,000 square foot lot with a 50-foot frontage, you may be allowed a .70 F.A.R. Multiply 6,000 sq. ft. x .70 = 4,200 sq. ft. of building area. From there, we subtract any existing structures to determine the potential size of an addition.

It’s important to note that these numbers are just examples. Each property needs to be reviewed individually to determine what’s truly possible. Beyond F.A.R., we also need to consider front, side, and rear yard setbacks, height restrictions, and any neighborhood overlay regulations. In addition, when a building is set close to a property line, fire safety codes and additional regulations apply.

Louisville Kentucky

Now Louisville Kentucky is a bit different. In Louisville we would need to reference the Louisville Development Code by the Louisville Metro Zoning Authority. We would look under the Site Design Standards. The allowable building area is based on a percentage of the open private yard available on the site. The website is a little challenging to search but if you google Louisville Development Code it will pop up.  

There are many moving pieces, but with the right process and guidance, we can identify exactly what’s possible for your lot and design a project that fits within those parameters.

If you have any further questions or if you feel I've written some information that is incorrect or not clear, please feel free to reach out with your questions or comments.

– Jason Zavala, Architect

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