ADUs
ADUs, garage apartments and backyard cottages, planned from the parcel up.
An accessory dwelling unit, ADU for short, is a zoning question before it is a design question. What your parcel allows is specific to your address, and it is the first thing we check.
Three forms, three problems
Almost everything we are asked for is one of three shapes, and which one you have decides what the drawing set contains, what the structure does, and where the money goes.
- A detached backyard cottage. Its own foundation, roof and utility runs. Nothing existing constrains the plan, which makes it the most flexible of the three and the most demanding of the lot: it has to fit inside the setbacks with the house already there, and the roof it adds counts against whatever impervious surface the lot is allowed, alongside the driveway and the paving.
- A garage conversion. The shell exists, which sounds like a saving and often is, but not a free one. A garage slab was poured to hold a car and sloped to drain out the vehicle door, and the walls were framed without the insulation or window openings a living space needs.
- An apartment above a garage. The hardest to answer quickly, because the question is whether the existing slab, footings and framing can carry a floor and roof they were never sized for. Sometimes they can. Often the answer is new foundation work.
How we draw one
It starts before the drawing board. We pull the parcel's zoning classification from the county GIS and read it against the local ordinance. Accessory dwelling rules are set by each jurisdiction, and the Triangle jurisdictions do not write them alike.
Setbacks are local too, not state, and they are measured to the farthest projection rather than the wall face, so decks and porches count. The foundation and setback topic covers that, plus frost depth and what the plot plan has to show.
With the site settled, the work runs the way our design projects run. Two design directions to react to, then one developed, then the permit set. Where the design goes past what the prescriptive framing tables in the adopted code cover, a stamped structural design comes in from a licensed professional engineer. On a garage picking up a floor, we plan for a stamp from the start.
If you only need the drawings, that is the permit drawings service. The permits guide lists what a residential submittal contains.
What decides the number
We price an accessory dwelling per project after a design call rather than publishing a band. The spread between the three forms, and between one existing garage and the next, is wider than one range could honestly describe.
Design fees are a separate line. Which package an accessory dwelling runs under depends on which of the three forms you have, and we name it in the written scope after the design call. Four things move the construction number more than anything else.
- Footprint. Every square foot carries foundation, roof and envelope, and a small building carries them at a worse ratio.
- Whether plumbing and a kitchen are added. Both bring supply, drain, vent and service into a structure that may have had none. That is the largest step between a studio and a one bedroom apartment.
- Whether the existing structure can carry what goes on it. The slab, footings and framing get evaluated before the plan is fixed. Reinforcing or replacing them is the item most likely to move a settled number.
- Utility connections. Water, sewer or septic, power, and sometimes a separate meter have to reach the new structure. How far it sits from the house, and what is already in the ground, is specific to the lot.
Who builds one
A parent moving closer without moving in. An adult child who needs somewhere to land. A unit to rent on a lot that already has room for one. A studio or office far enough from the house that the day ends when you cross the yard.
A unit for someone aging puts the bedroom, bath and entry on one level, with door widths and clearances drawn in from the start. A studio may not need a kitchen at all, and doing without one takes out the step above that moves the number most.
An addition answers the same question differently: more room attached to the house rather than a second structure in the yard. Which one is right is settled by the lot as often as by the program.
Questions we get asked
- Can I build an ADU on my lot?
- That is a question about your parcel, not about the city. The rules are set by each jurisdiction and differ across Raleigh, Cary, Durham, Chapel Hill and the counties around them. We read the zoning for your address against the local ordinance before we draw anything.
- Is converting the garage cheaper than building new?
- Usually, because the foundation, walls and roof already exist. The saving is smaller than it looks: ceiling height, insulation, window openings and the floor often all need work. We measure before saying which way is cheaper.
- Can my garage carry a second floor?
- Sometimes. The slab, footings and framing were sized for a one story structure, so whether they take a floor above is a structural calculation. That work is stamped by a licensed professional engineer, and we say at the start whether yours needs one.
- What does an ADU cost?
- We price it per project, in a written scope after a design call. The three forms differ enough that a published range would mislead more than help. Design fees are quoted with that scope, and every design package is published side by side on the packages and fees page.
- Do I need a permit?
- Yes. A new structure, or turning a garage into living space, puts the work in permit territory across the Triangle. Plan on a zoning review as well as a building review, and we confirm the specifics with the office that covers your address.
- Can you just do the drawings?
- Yes. That is the permit drawings service: you get the permit ready set, your builder prices and builds from it.
Keep reading
Send us the lot.
A photo of the backyard or the garage, and a sentence about who it is for, is enough to start. We reply within two business days.
Request a design call