Washington DC does not charge traditional development impact fees on residential construction, so accessory apartments are not subject to the impact, school, or transportation fees common in California, Colorado, and many suburban jurisdictions. The principal costs are DOB building-permit fees (scaled to construction value), DC Water meter and account fees if a separate meter is added, and standard utility connection charges. Historic district properties pay HPRB review fees.
Unlike many U.S. jurisdictions, the District of Columbia has not adopted impact-fee legislation under home-rule authority comparable to California's Mitigation Fee Act. DC funds infrastructure primarily through general taxation and special-assessment districts rather than per-unit impact fees, which keeps accessory-apartment soft costs lower than in many suburban jurisdictions. Costs an applicant should expect: (1) DOB building-permit fees calculated as a percentage of construction value (typically about 0.5 to 1 percent for residential, with minimum fees); (2) plan-review fees and any required surveyor fees; (3) DC Water charges if the unit requests a separate meter (account establishment fee, meter installation, and ongoing Clean Rivers Impervious Area Charge); (4) Pepco electrical service upgrades if needed; (5) HPRB review fee (currently around $34) for projects in historic districts. DC's recordation and transfer taxes do not apply to ADU construction itself. The Office of Tax and Revenue treats accessory apartments as part of the principal residence for property-tax purposes when owner-occupied; assessment uplift may occur after a Certificate of Occupancy is issued.
Unpaid permit fees: permit not issued. Unpaid DC Water charges: liens and shutoff. Failure to obtain Certificate of Occupancy: housing violations.
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See how Washington's adu impact fees rules stack up against other locations.
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