Home Addition - Zoning Requirements Research


Zoning refers to the set of rules, set by your local jurisdiction, that determine what kind of structure you can build on your property, how big it can be and for what it can be used. Building Code will provide your safe construction requirements, and along with Zoning make up the two most important sets of requirements that will guide your project.

Zoning research is one of the first things we do when beginning any new project. This is such an important part of the pre-design process that we typically do zoning research before we even know if we have been hired! In this post we’ll share a quick method of doing your own zoning research so that you can determine how much you might be able to build, before you talk with an architect or builder.


To begin your research, find your local zoning map. We’ll use the Montgomery County Zoning Map for this example.

Here's a link to the Washington DC Zoning Map.

First, find your address. There is a search bar along the top of the page. In this example I’m researching a property in Takoma Park. If you click on the plot of land, a lot of useful information is displayed on the left side of the map. Right away we can see we’re in zone R-60, which is the typical residential zone that governs much of lower Montgomery County.

On the left side, click on the blue text “R-60.” This will bring up the actual Zoning Ordinance. You’ll have to scroll down a little to find the R-60 section. You’re looking for Section 4.4.9. Residential – 60 Zone (R-60). You can also follow this link to a Montgomery County Zoning R-60 Cheat Sheet

Lot Coverage, Setbacks, Building Height

There are three main factors that will determine the size of addition you are allowed to build: Lot Coverage, Setbacks and Height

LOT COVERAGE: This is a percentage of your lot that is covered by a structure. The number of stories doesn’t matter here, just the footprint. Think of it as the amount of space on your property that doesn’t get wet when it rains. According to the zoning, you are allowed 35% lot coverage. (30% if your lot is less than 6,000 ft²) If we go back to the zoning map, with our address still selected, look for ACCT #: on the left under property info and click the blue number to the right. This will bring up the County’s property data for your address. Look for “Property Land Area” and you’ll see how big the county says your property is. For this example, it’s 5,016 ft². Zoning says I can have 30% lot coverage, so I know that I can build structure on 1,504 ft². To the left of Property Land Area will be the Above Grade Enclosed Area. This will be the county’s best estimate of the size of your house, not the footprint. Divide by the number of stories, or use information from a survey or plat to get your footprint. In this example I know the property is a single level, so the Above Grade Enclosed Area is equal to the footprint, or 21% of the lot. Therefor we could potentially build on 9% more of the lot, or 450 ft². Again, we could do two or three levels, but they would all be limited to that 450ft² size.

SETBACKS: This determines where on the property your structure can be located, and is fairly simple (unless you’re on a corner lot!) In R-60 your front setback is 25’ or the Established Building Line (EBL), whichever is greater. The EBL is the imaginary line that the front of all the adjacent houses create, if they are all the same distance from the curb. Your side setback is 18’ total, with no dimension less than 8’. That means you can’t get any closer than 8’ from the side of your property, and if one side of your house is only 8’ from your neighbor’s yard, the other side has to be at least 10’ from the other neighbor’s yard. Rear setback is 20’.

DC Zone R-1-B on the left, Montgomery County R-60 on the right. Notice the different Front Setback requirements. A clear Established Building Line is on the left.


HEIGHT: This one can be tricky because there are lots of different types of roofs and lots of variability to the slope of land on any particular plot of land. In R-60 your height is limited to 35’ or 30’ at the midpoint of a gable or hip roof. The height will typically be measured from an imaginary point that is the average of the grade around the perimeter of your house.

That’s zoning at its most basic. There are always special cases and different exemptions or requirements for every property. With this small amount of research however, you will have a pretty good idea if you are allowed to build a 2000 ft² guest house/art studio or a 200 ft² master bedroom and kitchen addition.

Let us know if you have any questions!