FAR3

Both of these designs have the same Floor Area Ratio but achieve it differently. The upper right design adds 800 sq. ft. to the top level. The upper right design adds 300 sq. ft. to the first level and 500 sq. ft. to the second. Both designs have a Gross Floor Area of 3200 sq. ft. and a Lot Area of 7000 sq. ft. making the FAR 3200/7000 or 0.45.

Deciding what can and can’t be built can be confusing. When creating a design for a remodel or custom home, one factor that many homeowners forget to consider is the local zoning restrictions on Floor Area Ratio (also called Bulk in some towns) or the ratio of living space in relation to the lot size. For homeowners who are considering a new project, understanding your local FAR restrictions (or whether there are any) can determine how much space can be added. Although definitions vary by community, we hope to help educate homeowners on the calculations of Floor Area Ratio in Chicago and its surrounding suburbs.

Understanding FAR Restrictions
FAR calculations are used to determine floor space in relation to the given lot size. These zoning restrictions are created by local municipalities primarily to prevent overbuilding the property. Generally, the maximum allowable Floor Area Ratios for residential properties are between 0.45 to .95 in the suburbs. This can basically be translated into the Gross Floor Area equaling 45% to 95% of the Lot Area. The FAR calculation is determined by the formula:

FAR = Gross Floor Area / Lot Area

Simple enough right? The complexity comes when you realize that each town can have different definitions of Gross Floor Area. Some count an open foyer as part of Gross Floor Area, others count a detached garage if it’s in the front 50% of the property.

What This Means for Your Remodel
Is your garage considered living space? What about the attic? Does a split-level change anything? Working with a Design/Build company that has experience with local zoning restrictions can eliminate having change paths after realizing that your design can’t be built in your town. Here at Airoom, we have a dedicated zoning specialist that researches the FAR restrictions for each community. Each design comes with a preliminary zoning report that outlines set-backs, FAR restrictions, impervious surfaces and more. This helps our designers ensure that we are designing to the zoning standards of each town, before presenting clients with designs.

Just as the main image illustrates, building up or building out can result in the same Floor Area Ratio, assuming the relationship between Gross Floor Area and Lot Area remain the same. So if building to the edge of your lot has less appeal than building up, FAR restrictions should not affect the ability to do so.

Resources for Understanding Your Town’s FAR Restrictions
Chicago Zoning Code Summary
City of Chicago Zoning Dept.
Illinois Municipalities


If you would like to learn more about a remodeling project and how it will work in your home contact Airoom today and receive a complementary design consultation. Or browse the remodeling galleries at Airoom.com.