Home Addition - One Project Start to Finish - Part 3

This is part three of a series of posts that will attempt to tell the story of one project from beginning to end, from concept to completion. It is based on a typical home renovation project in Montgomery County Maryland, but many of the issues convey to most jurisdictions throughout the United States.
Part 1: Inception
Part 2: An Actionable Plan


Montgomery County Zoning Map

Basic Zoning Research & Plats:

Zoning laws are in place to manage density and preserve or create neighborhoods, parks, commercial areas, etc. To this end, zoning laws will legislate how much structure you’re allowed to build on your property and for what it can be used. For this reason, zoning research must always be one of the very first steps when considering a potential addition. For a more detailed description of zoning requirements see our recent blog on Zoning Research.

When you buy a house, part of the settlement process typically requires a new survey to be done. A plat will be produced, which is a drawing that serves as a legal description of the property. This is done in metes and bounds. You can also search this link for your Montgomery County Plat.

Plat of a neighborhood in Takoma Park.

The plat will help your architect determine what size addition you will be allowed to build, based on zoning requirements such as setbacks and lot coverage. Although the zoning laws attempt to be as uniform as possible, every site is different and the zoning laws often require interpretation. For this reason, you may need to have some preliminary design work done that can be checked with the local authorities for conformance to the intentions of the local zoning regulations.

Increasingly such issues as water run-off, tree preservation, and other environmentally related areas of concern are being regulated and codified.


If for some reason you have a compelling need to do work that does not conform to the zoning regulations most jurisdictions have some type of variance process. To receive a variance you will typically have to show a reason why your design needs cannot be accomplished within the zoning guidelines, and even then you will typically have to show some type of hardship and probably have a public hearing.

Home Owners Association (HOA) Research:

Many established communities have Home Owners Associations (HOA) that have differing levels of jurisdictional authority with regard to what you can and can’t do to your property. Their mission is usually to keep the aesthetic feel of the community in tact by regulating how the “streetscape” feels. In many cases maintaining the neighborhood feel from the street becomes the primary mission of the HOA and though this can at times be constraining, it often lends to a stabilizing effect on property values.

Takoma Home Office field measure notes

House Measure and As-Built Drawings:

With some basic zoning research done it’s typically safe to proceed with the design portion of your project. The first step here is to get an accurate understanding of the existing conditions of your house. Existing plans will be helpful but your architect should be doing field measure verifications and developing their own set of “As-Built” plans upon which to base the renovation design work and drawings. We will come to your house and spend a few hours drawing your floor plan, measuring dimensions of all the rooms, doors, windows and taking tons of pictures. When we get back to the office we use these notes to create an accurate 3D model of your house. This model serves as a record of the As-Built conditions of your house and becomes the baseline for all design work moving forward.

Takoma Home Office Existing Conditions As-Built

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!