A home addition can be a great way to adapt your house to meet the changing needs of your family. There are several regulations that may impact the feasibility of an addition project. Many of these vary by jurisdiction and should be reviewed with a local design professional or code official to determine their impact on your project. This overview should help you understand what questions you might ask to determine what is possible for your home.
Zoning regulations often present significant limitations for an addition project and should thus be the starting point for determining what is possible. Specific constraints may be determined by the zoning designation of your lot, the date the lot was developed, or a combination of those and other factors. The most common zoning requirements for single-family residences include:
Setbacks– Setbacks or Building Restriction Lines (BRLs) dictate the minimum distances to property lines from the building or addition. In some cases the front setback may be a function of the distances of neighboring houses from the street. Corner lots, cul-de-sac lots, and flag lots may all have very specific setback requirements. Setbacks are typically quite different for a detached structure than they are for the primary structure. Porches and decks may be allowed to encroach on the setback in some jurisdictions.
Height controls– Most zoning codes limit building height, both in terms of a measured distance, and in terms of the number of stories. Different jurisdictions will have different ways of determining where to measure from and to, as well as what defines a story.
FAR– Floor Area Ratio is a calculation based on the total floor area of the house compared to the total lot area. FAR requirements are designed to limit bulk on a building site, and are more commonly used in urban areas than suburban or rural locations.
Lot coverage– Most zoning codes dictate how much of your lot can be covered by the home, or by total impervious area (including patios, walks and driveways), typically by defining a maximum percentage of lot coverage.
Dwelling units– Most zoning codes limit how many dwelling units can be located on a single lot. This may determine if you can add an in-law suite, second kitchen, guest apartment, etc.
Well and Septic
If your house is served by a well and / or septic system you will need to understand the location of both and determine the specifics of the septic system. The capacity of your septic system will dictate how much you can add, either in terms of bedroom count, bathroom fixture count, or square feet (depending on the jurisdiction). You will also have to maintain a minimum clearance from both the well and the septic tank and field with any new construction.
Local Design Review Boards
If your house is in a designated historic district, or a neighborhood with a home owner association (HOA) or design review board, you may need to start by seeing what types of projects are permitted within those guidelines. These boards will often impact if and where an addition can be located, as well what materials and aesthetic styles are acceptable or preferred.
Building Code Issues
Several elements of the building code may dictate how you configure an addition to your home. For example, if you expand a second floor on an older home, you may be required to bring the existing stairs up to the standards of the current code. This might make a first floor addition more feasible. Similarly, depending on the size of your project you may be required to add a fire sprinkler system, which often requires you to increase your incoming water service. These can be costly elements that you did not anticipate.
A thorough design process should begin with a review of each of these constraints, as well as your specific needs and budget, to determine the best design approach to achieve your goals for the project.
– Shawn Buehler, Principal