Guide to Washington, D.C. Zoning Code for Landscape Design (Part 2):
Lot Occupancy, Sheds, and What you Can Build in Required Yards
This article is continued from the guide to DC's Zoning codes, part 1. Please read that article first! Again, please reach out to me at renee@sandboxlandstudio.com if you'd like to set up a consult or inquire about a design. And again, make sure to confirm and/or clarify the code before making any decisions based on this information! Please reach out to me at the above email address if you discover the information is no longer correct or if links have broken.
So... where were we? To recap, we had just created this image, which showed the required yards, setbacks, and public parking areas for our rowhouse in zone R-2. But before we continue, I wanted to talk about two more things that can restrict how much we can build. I couldn't put them on the diagram because they're not dimensional in the same way.
Lot Occupancy Rules
DC does a good job of recognizing that it's an urban area and has many zones that are less restrictive in terms of where you can build than some of its suburban neighbors. However, the city doesn't want you to cover your entire lot with structures. The lot occupancy rules specify a maximum percentage of your lot that can be covered with buildings but gives you flexibility in where to site them.
You can find your maximum lot occupancy percentage on the interactive DC Zoning Map. We opened this in the previous article. Here's how to get to it again. Type in your address and scroll down on the left sidebar to the box that says 'Zoning/Land Use'. You will see a code with a R, like R-2. Click on that link and through to your development standards. For the R-2 zone I'm using as an example, the lot occupancy is 40%, which means that the buildings can't fill more than 40% of the lot. In denser areas, this number will be higher and in less dense areas the number will be lower.
Once you've located your property by typing in your address, click on the name of the zone below 'Zone District' on the left sidebar. Here it says R-2.
After clicking through 'See (your zone) Development Standards', you'll see a table of zoning information related to your property. This is really useful!
Rules for Lot Occupancy
Rules for lot occupancy can be found in 11-B311 Lot Occupancy under Definitions, Rules of Measurement, and Use Categories.
312 RULES OF MEASUREMENT FOR LOT OCCUPANCY
312.2 Lot occupancy shall be calculated by dividing the total building area, as defined by Subtitle B § 312.3, of all buildings on a lot by the total area of the lot.
312.3 For the purposes of lot occupancy calculation, building area shall be the maximum horizontal projected area of a principal building and its accessory buildings, measured at the ground level of the buildings and measured from the exterior faces of exterior walls and from the center line of walls separating two (2) buildings.
312.4 Building area shall not include:
(a) Building components or appurtenances dedicated to the environmental sustainability of the building;
(b) Cornices and eaves;
(c) Sills, leaders, belt courses, and similar ornamental or structural features;
(d) Awnings, serving a window, porch, deck, or door;
(e) Uncovered stairs, landings, and wheelchair ramps that serve the main floor;
(f) Chimneys, smokestacks, or flues; and
(g) Uncovered porches and decks that are no more than four feet (4 ft) in height above the ground level at any point.
Calculating Lot Occupancy
To calculate lot occupancy or lot coverage, we take the square footage of all building footprints and structures that are more than 4' above the ground and divide them by the square footage of the entire lot. Note that we don't use the square footage of the building as a whole, since the second story is stacked above the first! What we care about is the amount of space the building is taking up on the lot as viewed from the sky.
In the diagram, the lot is the entire yellow rectangle including the green area taken up by the building. It is a total of 3,256 square feet. Note that public parking area is not inside the property line and is not counted toward lot area! The rowhouse itself is 900 square feet. The front porch is less than 4 feet above the ground level but it is covered, so it is counted toward lot coverage. The deck in back is uncovered but higher than 4 feet above ground level, so it is also counted. Both front and rear steps are uncovered and serve the main floor so they are not counted. The total lot coverage is 1,085 square feet. 1,085 divided by 3,256 equals 33% lot coverage, which is less than the allowed lot coverage of 40%. These homeowners could have up to 217 more square feet of buildings or structures above 4' tall. They could add a shed and/or extend their deck.
Pervious Surface Rules
In general, DC doesn't want you to pave your entire property either. They would really prefer you maximize the amount of pervious/permeable surface, which allows water to percolate into the ground. If the entire city is impervious (made up of hard surfaces), rain runs off very quickly into storm sewers, causing rivers to flood rapidly and become contaminated with urban runoff. The city wants your lot to be able to absorb as much of the water that falls on it as possible. For the moment, pervious surface regulations are only applicable to fairly large development projects, for example if you're increasing lot occupancy by 10% or more or constructing a new house or accessory dwelling.
If these apply to you, you're probably hiring an architect, general contractor, or design professional who will help you navigate the regulations. Nonetheless, it's always a good idea to educate yourself. The definitions document clearly defines both permeable paving and pervious surface. The pervious surface section is tucked away under the 'General Rules' section at 11-C5. Even if these rules doesn't apply to you, I always try to maximize pervious surface whenever I can. Ecologically, it's the right thing to do. DC's Riversmart Homes program provides rebates for stormwater-friendly practices like rain barrels, permeable paving, and rain gardens.
A quick note that gravel is not pervious! This is a common misconception. Most gravel is angular, locks together, and is compacted in order to provide a stable base for cars, pedestrians, and other construction.
Decks, assuming they're built on a normal pier foundation over bare soil, are pervious because the water makes its way through the gaps between the deck boards and into the ground.
So What Can We Build, or My Favorite Part of the Code: Exceptions to the Rule
Is it weird to have a favorite part of the DC zoning code? Well, I do. The title of this section is called "Structures in Required Open Spaces" (11-B324), which doesn't sound very promising, but it tells you what structures you are allowed to build in your required yards. Hooray! Finally!!
324 STRUCTURES IN REQUIRED OPEN SPACES
324.1 Every part of a yard required under this title shall be open and unobstructed to the sky from the ground up except as follows:
(a) A structure that is no more than four feet (4 ft.) in height above the grade at any point, may occupy any yard required under the provisions of this title. Any railing required by the D.C. Construction Codes Supplement, Title 12 DCMR, shall not be calculated in the measurement of this height. This section shall not be used to exclude any portion of a building from lot occupancy calculations pursuant to Subtitle B § 312;
(b) A fence or retaining wall constructed in accordance with the D.C. Construction Codes Supplement Title 12 DCMR may occupy any yard required under the provisions of this title; and
(c) Uncovered stairs, landings, and wheelchair ramps that serve the main floor may occupy any yard required under provisions of this title. Any railing required by the provisions of the D.C. Construction Codes Supplement Title 12 DCMR shall be permitted.
Basically: In Washington DC, any structure that isn't an actual building and is four feet tall or less can be located in a required yard! Whew! That's a relief for a landscape designer who mostly deals with non-buildings that are low to the ground. To recap:
- Decks and uncovered porches four feet or less above grade can be located in any required yard. Best of all, railings don't count toward the height!
- Stairs, landings, and wheelchair ramps that serve the main floor of the house (the first floor) may be located in any required yard. This is particularly useful where the rear of the house is a full story below the main floor and many steps are required to access the house. You can then push a tall deck or addition out as far as possible and the stairs can project into the yard.
- Fences can logically be sited along property boundaries. I'll discuss fence height regulations in a later article. All fences must be permitted, although it's a fairly easy process.
- Retaining walls can be located where they're needed on the lot, although they're subject to many other additional height and permitting requirements.
- Small structures under 4' tall like bicycle storage or trash enclosures can be located in a required yard wherever it makes sense.
BUT REMEMBER! From the definition of yard wayyy back in the previous article, the sum total of all structures can't cover more than 50% of a required yard. To say it in a different way, the required portion of the yard must be at least 50% open to the sky. Usually, this isn't a huge burden but it's good to be aware of this fact.
Also remember! Just because you're allowed to put it in a yard by one set of regulations doesn't mean you'll be able to put it there in the end. The other regulations we discussed including lot coverage, permeable surface requirements, and public parking areas also come into play. If you're at the limit of your lot coverage or permeable surface requirements, you may not be able to add more structures or more impervious surface at all. I've seen this mostly when additions have maxed out the lot coverage. It then becomes very challenging, but not impossible, to fit everything in, much like a 3D game of Tetris!
How Big Can a Shed Be in Washington DC? Where Can it Be Located?
So that leaves sheds. Sheds are definitely structures. They are also usually over 4 feet tall. However, you'll be happy to learn that in Washington DC, sheds are not subject to the same setback requirements as other buildings (houses, garages, and accessory dwellings). Here's the definition of a "shed" from the definitions document:
Shed: An accessory building, not used for habitable or automobile purposes, that does not exceed 50 square feet (50 sq. ft.) in area and is less than 10 feet (10 ft.) in overall height.
In both R and RF zones, sheds are permitted within required rear and side yards. See the sections on rear and side yards in the accessory building regulations. These are in chapter 11-D50 (R zones) and 11-E50 (RF zones). Of course you will need a permit for any shed, but they are relatively easy to get.
5004.2 A shed may be located within a required rear yard of a principal building.
5005.2 A shed may be located within a required side yard of a principal building.
Note that if your "shed" is larger than 50 square feet, DC defines it as a garage or accessory building, not a shed, and additional permitting/requirements/setbacks will apply. For this information, take a look at the other sections on accessory dwellings. I do site garages and accessory dwellings, but they're outside of the scope of this article, which has already grown quite long.
I hope to follow up with another article with more dimensional information on retaining walls, fences, and other building code regulations, but not immediately. I'm feeling like some more 'fun' articles with pictures might be a treat after this tome! The exciting part is that I learned something new (about parking areas), which I'm happy to pass on to you.
While it seems like DC has a lot of regulations (and they do), they're actually doing a great job of streamlining regulations to make improvements less burdensome for homeowners and to make it so people with small properties can have things like sheds, patios, and fences that improve the quality of life in an urban area. The setbacks are often less stringent than those in neighboring municipalities. And they're really responsive to questions via email or phone call. I would recommend reaching out to them if you're confused about the regulations.
Again, if you have questions or a project you're struggling with, feel free to reach out to me at renee@sandboxlandstudio.com
I'd love to hear from you.
-Renee