IN 11 DCMR Subtitle U, Section U-253.7(a), the relevant table sets forth the minimum Gross Floor Area [GFA] required for a principal dwelling in order to have an accessory apartment use that is located in the principal dwelling unit’s building, for specified zones: 

U-253.7 An accessory apartment located in the principal dwelling shall be subject to the following conditions:  

(a) The house shall have a minimum of gross floor area, exclusive of garage space in the following zones: 

However, the table inadvertently omits 10 other R- zones, namely: 

R-6, R-7, R-8, R-9, R-11, R-12, R-14, R-15, R-16, R-21  

An Accessory apartment is a matter of right use in the above listed zones, as per U-253.1 and U-253.2: 

U-253.1 One (1) accessory apartment may be established in an R zone, subject to the provisions of this section. 

U-253.2 An accessory apartment shall be permitted in a principal dwelling or an accessory building as a matter of right in the R zones, except the R-19 or R-20 zones, subject to the provisions of this section. 

The Zoning Administrator has determined that the appropriate minimum GFA for the related principal dwelling unit for an accessory apartment is 1,200 sqft, which is the bottom portion of Table U-253.7(a).