Basement and attic dwelling units in Washington DC. Designed to be permitted, not just drawn.
Most owners assume the code is a wall of no. In much of DC it is not.
An accessory dwelling unit is a second, self contained residence on a property that already has a house on it. In the District that is usually a basement or a cellar level with its own entrance, sometimes an attic, occasionally a structure in the rear yard. The floor is already yours. What changes is whether it is legal to live in and legal to rent.
The distance between a finished basement and a permitted dwelling unit is not cosmetic. It is ceiling height, a second means of egress, fire separation between the units, alarms, light and ventilation, and a Certificate of Occupancy at the end. Any one of those can stop a project that has already been framed. All of them are cheaper to solve on paper.
I have designed dwelling units on Capitol Hill and near Dupont Circle, attic conversions in North Cleveland Park and Petworth. One architect on each of them, from the first walk-through to the last inspection.
In the rowhouse zones a second dwelling unit is frequently permitted by right, subject to lot area and to the zone the property sits in. In the lower density zones the path is different and often runs through a special exception.
Zoning is the first question and it is answerable in an afternoon. The second question is harder. Ceiling height, the location of the existing stair, where a window well can physically go, and whether the mechanical equipment can be relocated will decide the plan before anyone chooses a finish.
Below grade you start with limited daylight, a fixed ceiling, and columns and beams that cannot move. The plan has to place the entry, the kitchen, the bath and the bedroom so that none of them blocks the light the others need.
The difference between a unit that rents at the top of the market and one that sits empty is rarely the finish level. It is whether the space feels like an apartment or like a basement someone drywalled.
The drawings carry the plan, the sections, the details, the egress and separation strategy, and the mechanical, plumbing and electrical scope the reviewer needs to see. They are also what a contractor prices from, which is how you get comparable bids rather than three different guesses.
The direction of the money changes. You stop paying for that floor and the floor starts paying you.
In much of the rowhouse city a second dwelling unit is permitted by right, subject to lot area and to the zone the property sits in. It is not automatic and it is not universal, which is why the zoning check comes first.
Being allowed is only half of it. The unit also has to meet the residential code for egress, ceiling height, separation between the units and alarms, and it needs its own Certificate of Occupancy before it can legally be rented.
Habitable rooms generally require seven feet of clear ceiling height. Beams, ducts and pipes that hang below that line have to be dealt with, either by rerouting them or by planning the rooms around where they land.
Ceiling height is the most common reason a basement cannot become a unit without underpinning or lowering the slab, and both of those are structural work with real cost. Measure this before you fall in love with the idea.
Every sleeping room below grade needs an emergency escape and rescue opening. In practice that is an egress window with a window well sized so a firefighter can get in and an occupant can get out, unless the room opens directly to an exterior door at grade.
Where that window can go is a site question as much as a code question. Setbacks, the neighbour's wall, the areaway and the existing foundation all limit it, and the answer often reshapes the plan.
A contractor builds what the drawings say. The decisions that determine whether the unit is legal, rentable and worth living in are made before the drawings exist, in the layout, the zoning path and the code strategy.
Those decisions are far cheaper to make on paper than in the field. A wall moved in a drawing costs an hour. The same wall moved after framing costs a change order and a schedule.
Design and permit drawings typically run a few months depending on how much survey and existing condition work is needed up front. Permit review in the District adds its own time and it is not fully predictable.
Construction depends on scope. A unit that needs underpinning, a new egress well and a relocated mechanical room is a different job from one where the ceiling height and the entry are already there.
"It was difficult, even for us, to see the potential in a dim, damp and crowded basement. But I knew the apartment was already in there."
Luis Boza · On the first walk-through
Have a floor doing nothing?
Start with the zoning. It is the cheapest question to answer and it decides everything after it.
Read what your zoning allows →Rather talk it through? Start with one question.