Zoning Lots Divided by District Boundaries (ZR Article VII, Chapter 7)

A district line through a lot does not have to cut its development potential in two; ZR Article VII, Chapter 7 decides how the rules combine.

When Article VII, Chapter 7 applies

District boundaries on the zoning map often run through the middle of lots, commonly 100 feet back from an avenue. Whenever a zoning lot is located in two or more districts with different uses permitted, or with different use, bulk, parking and loading or other rules, ZR Article VII, Chapter 7 applies (ZR 77-01). The residence district chapters point there too: ZR 23-04 for residential bulk and ZR 24-17 for community facility bulk.

The first question is the lot's history. If the zoning lot did not exist on December 15, 1961, or on the date of the amendment that put the boundary through it, each portion is simply regulated by its own district, with one exception: the FAR averaging in ZR 77-22 applies to zoning lots created at any time (ZR 77-02). If it did exist on that date, the more flexible rules below can apply (ZR 77-03).

The 25-foot rule: one district for the whole lot

• Uses (ZR 77-11): for a lot existing on the key date and split between districts with different permitted uses, the use rules of the district holding more than 50% of the lot area may apply to the entire lot, provided the greatest distance from the mapped boundary to any lot line in the minority portion is no more than 25 feet, measured perpendicular to the boundary. The boundary is then treated as moved, and that district's bulk, parking, loading and other rules apply to the whole lot.
• One- and two-family districts next to apartment districts (ZR 77-11): instead, R3-2 use and bulk rules apply in an R1, R2, R3A, R3X or R3-1 portion, and R4 rules apply in an R2X, R4A, R4-1 or R4B portion.
• Bulk only (ZR 77-211): the same 50% and 25-foot test lets one district's bulk rules apply to the whole lot where the split is between two residence districts limited to single- or two-family homes, or between two commercial or two manufacturing districts that permit the same uses.
• Special districts: unless a special purpose district says otherwise, these rules also apply to lots divided by a special purpose district boundary (ZR 77-11, 77-211).

FAR averaging (ZR 77-22)

When the lot stays split, the maximum FAR for each portion is multiplied by that portion's share of the zoning lot, and the products are added to get an adjusted maximum FAR. That floor area can go anywhere on the zoning lot, subject to all other rules, as long as no portion exceeds the greater of its own district FAR or the adjusted FAR. A portion fronting on and within 100 feet of a wide street, and permitting the higher residential FAR, may exceed its own residential FAR by up to 20 percent (ZR 77-22).

A worked example

A 10,000 sq ft zoning lot has 6,000 sq ft in an R7A district (standard FAR 4.00) and 4,000 sq ft in an R6B district (standard FAR 2.00) (ZR 23-22). The R6B part is 40 ft deep, so the 25-foot rule does not apply.

• Total floor area: 10,000 x 3.20 = 32,000 sq ft (ZR 77-22).
• Without averaging, the R7A part alone could hold 24,000 sq ft (6,000 x 4.00) and the R6B part 8,000 sq ft (4,000 x 2.00). The total is the same 32,000 sq ft, but averaging lets floor area move.
• The R6B portion may now hold up to 3.20 FAR, the greater of 2.00 and 3.20, or 12,800 sq ft (4,000 x 3.20), but R6B height and setback limits still apply there, because neither district uses sky exposure planes (ZR 77-28).
• Units: each portion is counted under its own rules and added (ZR 77-25). R7A: 24,000 / 680 = 35.29, so 35. R6B: 8,000 / 680 = 11.76, so 12. Total 47 units (ZR 23-52).

Height, density and other rules

• Height and setback (ZR 77-28): where every district on the lot uses sky exposure planes, the quantitative height and setback requirements on each street frontage are averaged by share of frontage. Otherwise each portion keeps its own height rules. If more than 50% of the lot is in R2X, R3, R4, R4-1 or R4A and the minority portion is no more than 25 feet deep, that district's height rules may apply to the whole lot.
• Density (ZR 77-25): the maximum number of dwelling units is the sum for each portion, and units may go wherever a building is permitted on the lot. Where a portion is limited to single- or two-family homes, only one or two units may be provided there.
• Uses that cannot use the 25-foot rule (ZR 77-12): each district's use rules stay on its own portion, except under special permits in ZR 73-42 and 73-52.

What to check first

Find exactly where the boundary falls (the zoning map or a survey), the area and depth of each portion, and whether the zoning lot existed on December 15, 1961 or on the date of the amendment that drew the line. That history is what unlocks the 25-foot rule.

Split lot FAQ

Related pages

• Wide vs narrow street
• Dwelling unit factor
• R7A zoning
• R6B zoning
• R4 zoning