The short answer
Architect fees in the Washington DC metro run about $5,000 to $11,250 to design a 600 square foot ADU and $4,150 to $31,200 for a 2,500 square foot new home. Building that detached ADU costs roughly $93,600 to $156,000. Your address decides which rules apply, because DC, Maryland and Virginia each have their own ADU law, permit office and license board.
What architects and ADUs cost in Washington DC
These figures come from national cost data multiplied by the metro's construction cost factor of 1.04 from the U.S. Army Corps of Engineers Area Cost Factors. Design fees and build costs are separate, since you usually pay the architect months before a builder starts.
| Job | Washington DC (typical range) | US average |
|---|---|---|
| Architect fees, ADU (600 sq ft) | $5,000–$11,250 | $4,800–$10,800 |
| Architect fees, addition (500 sq ft) | $3,100–$7,800 | $3,000–$7,500 |
| Architect fees, new home (2,500 sq ft) | $4,150–$31,200 | $4,000–$30,000 |
| 3D rendering package | $830–$3,350 | $800–$3,200 |
| Prefab ADU, 600 sq ft, built | $49,900–$99,850 | $48,000–$96,000 |
| Garage conversion ADU, 600 sq ft | $31,200–$124,800 | $30,000–$120,000 |
| Attached ADU, 600 sq ft | $78,000–$140,400 | $75,000–$135,000 |
| Detached ADU, 600 sq ft | $93,600–$156,000 | $90,000–$150,000 |
| ADU above a garage, 600 sq ft | $124,800–$312,000 | $120,000–$300,000 |
| Land survey | $415–$1,850 | $400–$1,800 |
Estimates for 2026, including labor and standard parts. Washington DC prices use the metro's construction cost factor of 1.04 (US average = 1.00) from the U.S. Army Corps of Engineers Area Cost Factors. Your quote depends on access, materials and the condition of the home.
The cost estimator below works from your project type and ZIP code. The architecture cost estimator page has a longer version.
How architects here charge
HomeGuide's national figures put residential architect fees at 5% to 20% of construction cost, $2 to $15 per square foot, or $100 to $250 an hour. The fee is usually split by phase:
| Phase | Share of the fee | What you get |
|---|---|---|
| Schematic design | 20% | Layout options, massing, early cost check |
| Design development | 10% | Materials, windows, structure and systems |
| Construction documents | 40% | The permit set and the drawings builders price |
| Bidding | 5% | Help comparing builder bids |
| Construction administration | 25% | Site visits and answers during the build |
A rowhouse lot in DC or Alexandria, a slope lot in Arlington or a lot with mature trees in Bethesda usually needs a survey, engineering and a second round of review, which pushes the fee toward the top of each range. The architecture pillar page compares fees across project types.
What the build costs
A 600 square foot prefab ADU runs about $49,900 to $99,850 built. A garage conversion runs $31,200 to $124,800, an attached ADU $78,000 to $140,400, a detached ADU $93,600 to $156,000, and an ADU above a garage $124,800 to $312,000. A land survey, which most jurisdictions want before a new structure is sited, runs $415 to $1,850. A 3D rendering package runs $830 to $3,350.
How ADU rules differ across the metro
The same 600 square foot plan can be allowed on one side of a street and barred on the other, because each jurisdiction writes its own rules.
District of Columbia
DC issues building permits through the Department of Buildings (DOB). New construction and additions pay a permit fee of $0.03 per cubic foot of construction plus a 10% enhanced fee, and new construction and alterations require a filing deposit of 50% of the assessed permit fee based on estimated construction cost, capped at $20,000, plus 10%. An alteration or repair permit for construction valued between $1,001 and $1 million costs $30 plus 2% of construction value, plus 10%. A new garage or shed permit is $65, or $71.50 with the enhanced fee.
DC also charges a Green Building Fee of $0.002 per square foot of construction on new construction, plus 10%, and a Certificate of Occupancy for 5,000 square feet or less costs $42 plus a $33 filing fee, plus 10%.
The DOB Homeowner's Center handles one- and two-family projects and can review interior remodeling up to 500 square feet, one-story additions up to 500 square feet, decks under 500 square feet and under 10 feet above grade, and window and door replacement. DOB aims to issue those permits within five business days. The general line is (202) 671-3500.
Plumbing, mechanical and electrical permits are trade permits issued only to licensed and bonded master trade professionals, and homeowners cannot apply for them.
Maryland: Montgomery and Prince George's counties
Maryland's Accessory Dwelling Units Act of 2025 (House Bill 1466) was signed in April 2025 and took effect October 1, 2025. It requires counties and municipalities to adopt local laws by October 1, 2026 authorizing ADUs on land with a single-family detached dwelling. Until your county's local law is in place, ask the county which rules it enforces.
Montgomery County already has detailed ADU rules through its Department of Permitting Services (DPS). An ADU must be licensed by the county's Department of Housing and Community Affairs before you apply for a building permit. Only one ADU is allowed per lot, and it may not be greater than 75% of the size of the primary house. A detached ADU needs an approved NFPA 13D fire sprinkler system and a separate fire protection permit. A drainage plan is required for a detached ADU regardless of size, and an engineered sediment control permit is required once construction disturbs 5,000 square feet or more. On a septic-served lot, the ADU needs its own septic reserve area and a new system under a new permit. Private deed restrictions in many subdivisions can add rules beyond the county's, and the county does not enforce them.
Prince George's County permits run through the Department of Permitting, Inspections and Enforcement (DPIE). A one-story detached accessory structure under 150 square feet, not meant for habitation, is exempt from a permit, one per property. A permit under which no work has started within 180 days of issuance expires.
Virginia: Arlington, Fairfax and Alexandria
Virginia localities work under the 2021 Virginia Uniform Statewide Building Code, which took effect January 18, 2024 and has applied to all permits since January 18, 2025. Each city or county building official enforces it: Fairfax County Land Development Services, Arlington's Permit Arlington center, and Alexandria's own building office.
Local zoning sets the ADU limits. In the City of Fairfax, only one ADU is allowed per lot, its gross floor area may not exceed 35% of the house's gross floor area, and it may not have more than two bedrooms. The lot needs at least two off-street driveway spaces, the owner must live in either the house or the ADU, and a detached ADU must sit at least 20 feet from the rear lot line and no more than 20 feet tall. Alexandria approved its ADU ordinance in January 2021, requires owner occupancy at the time the ADU is built, and prohibits exclusive use of an ADU as a short-term rental.
Virginia also exempts much residential work from the architect license requirement. Under Code of Virginia 54.1-402, no architect or engineer license is needed to prepare plans for single- and two-family homes, townhouses and multifamily dwellings up to three stories, excluding electrical and mechanical systems, or for additions, remodeling or interior design with no change in occupancy, structure, exits or fire hazard, as long as the plans carry the author's name, address and occupation. Our ADU design guide covers layouts and cost-saving choices.
Do you need a permit?
Any ADU, addition or new home needs a permit in all three jurisdictions. Who reviews it and how long it takes varies.
| Your address | Permit office | What to expect |
|---|---|---|
| Washington DC | DC Department of Buildings (DOB) | Homeowner's Center for small jobs, five business days target; full review for larger work |
| Montgomery County, MD | Department of Permitting Services (DPS), 2425 Reedie Drive, Wheaton; 240-777-0311 | Online application and ePlans upload; inspections requested at least 24 hours ahead |
| Prince George's County, MD | DPIE | County review; WSSC Water handles plumbing and gas permits |
| Arlington, VA | Permit Arlington (Accela portal) | County review under the USBC |
| Fairfax County, VA | Land Development Services, 703-222-0801, PLUS system | County review under the USBC |
| Alexandria, VA | City building office | City review under the USBC |
In DC, other agencies can join the review. DC Water reviews new water connections, DDOT reviews public space and alleys, the Historic Preservation Review Board and the Commission of Fine Arts review historic and federal work, WMATA reviews projects next to Metro property, and DOEE reviews soil disturbance, flood plains and lead abatement. You can check whether a property is in a historic district or flood hazard area in DOB's Scout tool.
In Maryland, the Maryland Building Performance Standards adopt the 2021 IBC, IRC and IECC with state modifications, and each county enforces them with its own amendments. In Virginia, the USBC requires a permit for construction, demolition and alterations involving walls, structural components, means of egress, water supply, drainage, electric wiring or mechanical and fuel systems. Emergency repairs may start first, with the application filed by the end of the first working day.
Our guide to permit drawings lists what a complete set includes.
Historic districts, slopes and stormwater
Historic districts
In DC you need historic preservation review when a building permit is needed for work affecting the exterior appearance of a historic property. There is no separate preservation permit: the Historic Preservation Office's clearance of the DOB permit is the approval. "Postcard" permits cannot be used on a historic property. Window and door replacement in a historic or Commission of Fine Arts area needs that approval before you apply for the permit. The Office of Planning is at 899 North Capitol Street NE, Suite 7100, (202) 442-7600.
In Virginia, the building official may require a permit for replacement siding, roofing and windows that the USBC otherwise exempts when the house is in a locally designated historic district. Alexandria's Old and Historic District adds its own review.
Slopes, trees and stormwater
Montgomery County's drainage plan rule applies to a detached ADU of any size, and to additions that increase a single-family footprint by more than 400 square feet on lots under 15,000 square feet without an approved stormwater plan. Prince George's County exempts retaining walls 2 feet or less in height unless they support a structure, and fences 4 feet or less. In DC, retaining walls, fences and sheds all need permits.
Before anyone digs, call 811. In DC, Miss Utility wants at least four days' notice. In Maryland, contact Miss Utility no sooner than 3 business days and no later than 12 business days before digging. In Virginia, work may begin 48 hours after a locate request.
Structural and energy code coordination
Every jurisdiction in this metro is in climate zone 4A, mixed-humid, so plans carry both heating and cooling loads. Reagan National averages 3,769 heating degree days and 1,738 cooling degree days. The suburbs are colder: Dulles averages 4,604 heating degree days and gets about 21 inches of snow a year against 13.7 at the airport. That affects insulation, window and foundation detailing in the permit set.
Many projects need a structural engineer, especially second stories, above-garage ADUs and anything on a slope. HomeGuide puts structural plans at $500 to $3,000 for an average house or remodel, and most engineers will not stamp plans they did not create or supervise. Our guide to structural coordination explains how the engineer's drawings fit into the architect's set. To see the unit from the main house or the street before the layout is fixed, ask about 3D renderings.
How to check an architect before you hire
Each state licenses architects separately and keeps its own lookup.
- DC: the Board of Architecture, Interior Design, and Landscape Architecture at the Department of Licensing and Consumer Protection regulates the practice. No one may practice architecture in DC or use the titles "architect," "registered architect," "licensed architect" or "architectural designer" unless licensed. The license fee is $120 for up to two years, renewal is $155, and licenses expire April 30.
- Maryland: the Maryland Board of Architects licenses individuals and also issues permits to businesses practicing architecture. Application costs about $76 to $126. Search the state's universal license lookup by last name. The Board investigates complaints against licensees and complaints about unlicensed practice, and can reprimand, suspend or revoke a license or permit, or impose a fine. Phone 410-230-6261.
- Virginia: architects are licensed through the APELS board at the Department of Professional and Occupational Regulation. Use the DPOR license lookup. Phone (804) 367-8511.
Ask for a written contract before work starts. In DC, regulations require a written contract signed by both sides before a contractor accepts payment, listing the contractor's name, address, phone and DC license number. In Maryland, every home improvement contract must be in writing and include the contractor's MHIC license number, start and completion dates, the work and materials, the price and payment details, and the right to buy a performance bond. In Virginia, the contract must state the amounts and schedule of progress payments including the down payment, the contractor's license number, class and specialties, and a notice of the Virginia Contractor Transaction Recovery Fund.
Ask who will draw the structural sheets and the energy compliance documents. Ask for projects similar to yours, especially rowhouse, historic or slope work if that applies. Interior-only projects are covered in our Washington DC interior designer guide.
Areas we cover
GOLDGCP architects and vetted pros work across the Washington DC metro, including:
- Washington DC
- Arlington
- Alexandria
- Fairfax
- Bethesda
- Silver Spring
- Northern Virginia
- Montgomery County
Each jurisdiction runs its own permit office and ADU rules. Enter your ZIP code to see local prices.
How GOLDGCP works
- Tell us about the lot and the project.
- Our in-house architects check zoning, ADU rules, historic status and stormwater requirements for your jurisdiction, then draw the permit set.
- We match you with up to 3 vetted, licensed pros and show prices by ZIP code before anyone visits.
- You approve each stage and pay your pro directly, milestone by milestone, tracked in the client portal. The payment protection page explains how milestones work.
Pros pass six-step vetting first: state license verification, an insurance check, a background and business check, portfolio review, client reference calls, and onboarding with a quality score. GOLDGCP is free for homeowners and serves all 50 states, with a 24/7 emergency line.
Frequently asked questions
How much does an architect cost in Washington DC?
About $5,000 to $11,250 for a 600 square foot ADU design, $3,100 to $7,800 for a 500 square foot addition, and $4,150 to $31,200 for a 2,500 square foot new home, using national data at the metro's 1.04 cost factor.
How much does it cost to build an ADU in Washington DC?
A 600 square foot detached ADU runs about $93,600 to $156,000 built, an attached ADU $78,000 to $140,400, a garage conversion $31,200 to $124,800, and a prefab unit $49,900 to $99,850. Design, survey and permit fees are extra.
Do I need an architect for an ADU in Northern Virginia?
Not always. Virginia exempts single- and two-family homes, townhouses and dwellings up to three stories from the architect license requirement, and additions with no change in occupancy, structure, exits or fire hazard, as long as the plans carry the author's name, address and occupation.
What are the ADU rules in Montgomery County?
One ADU per lot, no larger than 75% of the primary house, licensed by DHCA before the building permit. A detached ADU needs NFPA 13D sprinklers and a drainage plan. Maryland's state ADU law requires county rules by October 1, 2026.
How long does a DC building permit take?
The DOB Homeowner's Center aims to issue permits for small one- and two-family projects, including interior remodels and one-story additions up to 500 square feet, within five business days. Larger projects go through full plan review.
How do I check an architect's license in Maryland?
Search the Maryland Department of Labor's universal license lookup by last name. The Maryland Board of Architects licenses individuals and permits architecture firms, and it investigates complaints against licensees and unlicensed practice. The Board's phone is 410-230-6261.
Does a historic district change my project in DC?
Yes. Work affecting the exterior of a historic property needs Historic Preservation Office clearance of the DOB permit. There is no separate preservation permit. Window and door replacement in a historic or Commission of Fine Arts area needs approval before you apply.
How we calculate these prices
GOLDGCP starts from national price ranges for each job, taken from published 2026 cost guides and checked against local price guides where they exist. To get a local price, we multiply the national range by the construction cost factor for the metro from the U.S. Army Corps of Engineers Area Cost Factors (US average = 1.00). Where that table has no entry for a metro, we use the nearest listed location or the state value. For ZIP codes outside the 50 largest metros, the cost estimator uses the state's price level from the Bureau of Economic Analysis Regional Price Parities. Ranges include labor and standard materials but not unusual site conditions, so a written quote after an inspection is always the final price.
Sources
About this guide
Written by the GOLDGCP editorial team. Prices come from national cost guides adjusted with official construction cost factors for Washington DC; rules and statistics come from the agencies and reports linked in the text. We update this page when prices or codes change.
