While designing a new house, it is important to know the regulations associated with the purchased lot. Some of these may be based on local zoning regulations, while others may depend of more tangible aspects like adjacent buildings or infrastructure. The following example shows a basic calculation of how to determine the size of a house on a plot:
If your local regulatory body defines the following constraints:
- Building coverage = 50%
- Floor Area Ratio = 1.5
- Maximum Building Height = 26 foot
- Minimum Front Setback ≥ 10 foot
This means that on a 2000sqft lot, you could utilize 1000sqft of space on the ground floor (building coverage).
Since your FAR is 1.5, the total buildable area including all floors is 3000sqft.
As the maximum permissible height is 26 foot, you may be able to utilize this 3000sqft spread across two floors and probably an attic.
Constraints are placed on the size (height and shape too) of a house to control the density of a neighborhood. This ensures adequate access to natural light, ventilation and privacy to all residents. They make sure that infrastructure like roads, water and electricity are not burdened.
Regulations vary widely in different parts of the country. You may even notice that they differ in the adjacent block or street. Information pertaining to your lot should be sourced from your local governing body. This could be a county, municipality or even your local ‘Home Owners’ Association’.
Let’s take a brief look at some of these. As you read through this article, please keep in mind that the terminology and values used here are generalized and may vary in your locality.
Building Coverage / Site Coverage
Coverage refers to the area of the site covered by the built structure. This includes all pertinent structures like awnings, cantilevered extensions, covered car parks etc.
Site coverage is a similar concept. It includes impermeable surfaces like pavements and parking in addition to built form. The value of coverage is usually expressed in percentages. Coverage helps in maintaining a balance between the built and green (permeable) environment of a place.
This is one among the first constraints that a building designer places on the drawing board. Setbacks specify the minimum mandatory yards that are to be left vacant on all sides of the house. They are measured from the boundary edges.
The front setback generally has the largest value. This can range from less than a meter (in dense urban settlements) to more than 15 meters (in large estates). Front setbacks of existing residences on adjacent plots are also considered for determining the permissible setback for your plot. In some places, this is measured based on the abutting street rather than the property line. The sides and the back values are usually smaller than the front setback.
If you own a corner lot, you may have to consider both the yards abutting the road as the front. In other places, you may have the right to choose one and in yet others, the front will be the one abutting the wider road.
At this point, you may naturally question, what is the logic of a setback? Why is it imposed on private property?
Setbacks account for both aesthetics and function. Having all the residences on a street behind a particular line enhances visibility. It decreases clutter and creates potential for a beautiful streetscape. Side & back setbacks help in maintaining privacy between adjacent homes. It also ensures adequate light and ventilation to all sides of the house.
|District||Minimum Front Setback|
|RS1 to RS3||20 feet or 16% of lot depth, whichever is less|
|RT3.5 to RM6.5 + DR||15 feet or 12% of lot depth, whichever is less|
|District||Minimum Side Setback|
|RS1||Detached house: Combined total width of side setbacks must equal 30% of lot width with neither required setback less than 5 feet or 10% of lot width, whichever is greater|
|RS2||Detached house: Combined total width of side setbacks must equal 30% of lot width with neither required setback less than 4 feet or 10% of lot width, whichever is greater|
|RS3||Detached houses: Combined total width of side setbacks must equal 20% of lot width with neither required setback less than 2 feet or 8% of lot width, whichever is greater|
Beyond visuals, front setbacks are also essential for utility easements. These include water connections, electricity lines and storm water drains. Setbacks are also utilized for street widening if the need arises.
Flood plains, rivers & water bodies, ecologically sensitive areas and hazardous zones like cliffs are a few other areas that have strict regulations regarding setbacks.
Setbacks work in tandem with and inversely proportional to an important factor:
Building height is also a component of size. The taller your house is, (i.e. more number of stories), the smaller its footprint should be, by rule.
The setbacks increase up to a certain limit and ceases. Floors can be added beyond this without increase in setback based on other factors like FAR and land use (e.g. Apartments, high-rise office buildings).
This relation between setbacks and height helps the street keep a control over building density and population. This also makes sense in an emergency when fire trucks could occupy the setbacks to access higher floors.
Building height is restricted in areas close to airports, military facilities and areas of national importance. The same applies to Historical and Heritage building locales.
Floor Space Index / Floor Area Ratio
FAR and FSI are different terms for the same concept.
FAR is the ratio of a building’s total built-up area to the area of the plot it is being built on. Built-up area is the sum of areas of all floors in the building. FAR is denoted by a ratio and FSI is an index shown in percentage.
For example, if your plot is of 2000sqm in area and FAR is 1:0.8, your house can be built to a total of 1600sqm divided among all floors.
This ratio helps in controlling the density of a neighborhood. It will be available with your local governing authority and in their online archives. As with all factors discussed yet, the value of FAR/FSI varies from place to place based on Zoning and Land Use maps.
Off-street parking is another factor that affects the size of the house.
The larger the house, more the number of parking spaces to be provided. Consequently, more the number of parking, lesser the actual building footprint can be.
Utilities include structures and facilities that support the functioning of a house. Examples of these are sump tanks, septic tanks, wells, fire hydrants, generators, gas pipes etc.
Based on the location of your lot, features like wells or septic tank has to be at a mandatory stipulated distance from each other and other built form. This is to prevent cross-contamination and/or damage to other structures.
This in turn constricts the area of the building foot print. If you are in a zone with severe height restrictions, this is going to affect the overall size you can build.
Each of the factors covered above have been carefully articulated by various planning commissions and governing bodies after years of research and design. The logic behind them is focused on both functional and aesthetic aspects. These factors can vary based on the location, building typology and land use zone.
Finding the right size for your house is a balancing act which satisfies the conditions put forward by these regulations. If they seem too complex, a skilled professional will be able to crunch these numbers and arrive at a size that suits your needs and adheres to the rules
AMERICAN SOCIETY OF PLANNING OFFICIALS. (1958). Floor Area Ratio (Information Report No. 111). CHICAGO, ILLINOIS.
AMERICAN SOCIETY OF PLANNING OFFICIALS. (1952). Minimum Requirements for Lot and Building Size (Information Report No. 37). CHICAGO, ILLINOIS.
Chicago Zoning Ordinance (Vol. Bulk and Density Standards). Chicago.
Crawford, J. (n.d.). FAR Explained. Retrieved from Car Free: https://www.carfree.com/far.html
Law Insider. (n.d.). Site Utilities definition. Retrieved from Law Insider: https://www.lawinsider.com/dictionary/site-utilities
Meriam, D. (2004). The Complete Guide to Zoning. McGraw-Hill.