D.C. Mun. Regs. tit. 11, r. 11-414
The owner of a non-residential building proposing to construct penthouse habitable space shall produce or financially assist in the production of residential uses that are affordable to low-income households, as those households are defined by § 2601.1, in accordance with this section.
The requirements of this provision shall be triggered by the filing of a building permit application that, if granted, would result in the amount of penthouse habitable space exceeding one thousand square feet (1,000 sq. ft.).
The requirements of this section shall not apply to properties owned by the District government or the Washington Metropolitan Area Transit Authority and used for government or public transportation purposes.
Qualifying residential uses include one (1)-family dwellings, flats, multiple-family dwellings, including apartment houses, rooming houses, and boarding houses, but shall not include transient accommodations, all as defined in § 199.1.
If the owner constructs or rehabilitates the required housing, the provisions of §§ 414.6 through 414.11 shall apply.
The gross square footage of new or rehabilitated housing shall equal:
If the housing is provided as new construction, the average square feet of gross floor area per dwelling or per apartment unit shall be not less than eight hundred and fifty square feet (850 sq. ft.); provided, that no average size limit shall apply to rooming houses, boarding houses, or units that are deemed single-room occupancy housing.
For purposes of this section, the word "rehabilitation" means the substantial renovation of housing for sale or rental that is not habitable for dwelling purposes because it is in substantial violation of the Housing Regulations of the District of Columbia (14 DCMR).
In the case of rental housing, the required housing shall be maintained as affordable dwelling units for not less than twenty (20) years beginning on the issuance date of the first certificate of occupancy for the residential development, or if for a one (1)-family dwelling, the effective date of the first lease agreement.
If the required housing is provided for home ownership, it shall be maintained as affordable dwelling units for not less than twenty (20) years beginning on the issuance date of the first certificate of occupancy for the residential development, or if for a one-family dwelling, the effective date of the first sales agreement.
No certificate of occupancy shall be issued for the owner's building to permit the occupancy of penthouse habitable space until a certificate of occupancy has been issued for the housing required pursuant to this section, or in the case of a residential unit for which a certificate of occupancy is not required, prior to the final building inspection.
If the owner instead chooses to contribute funds to a housing trust fund, as defined in § 2499.2, the provisions of §§ 414.13 through 414.16 shall apply.
The contribution shall be equal to one-half (1/2) of the assessed value of the proposed penthouse habitable space.
The assessed value shall be the fair market value of the property as indicated in the property tax assessment records of the Office of Tax and Revenue no earlier than thirty (30) days prior to the date of the building permit application to construct the penthouse habitable space.
The contribution shall be determined by dividing the assessed value per square foot of land that comprises the lot upon which the building is or will be located by the maximum permitted non-residential FAR and multiplying that amount times the penthouse habitable space to be constructed.
Not less than one-half (1/2) of the required total financial contribution shall be made prior to the issuance of a building permit for construction of the penthouse habitable space, and the balance of the total financial contribution shall be made prior to the issuance of a certificate of occupancy for any or all of the building's penthouse habitable space.
D.C. Mun. Regs. tit. 11, r. 11-414