Sliver law affects dense residential districts including R7-2, R7D, R7X, R8, R9 and R10 according to ZR 23-692. In those residential districts, portions of buildings with street walls less than 45 feet in width shall not be permitted above certain heights depending on the width of the street. A street width that is 75 feet or more is considered as a “wide street” and a street width that is less than 75 feet is considered as a “narrow street’. The maximum height of the building shall be equal to the width of the street or 100 feet, whichever is less. For example: if the street width is 60 feet, then the building affected by sliver law shall have a maximum height of 60 feet. Through conventional residential developments, 60 feet equals to 6 stories assuming 10 feet each per floor. For through lots, it shall be treated as two interior lots with equal depths and different street widths. Corner lots that front two streets, will have the maximum height equal to the narrowest of such streets if it is bounded by only narrow streets. However, if the lot is bounded by one wide street, the maximum height of the building shall be equal to the height of the widest street on which it fronts or 100 feet, whichever is less. 

Recently, Development Site Advisors sold a site – 303 East 111th Street – that is subjected to sliver law in East Harlem for $1,750,000 or $142/maximum allowable ZFA. The zoning is R9A/R7A/C2-5 which technically allows a maximum residential ZFA of 23,231sf. Unfortunately, with 27 feet of frontage, the site is subjected to sliver law that allows a maximum ZFA of 12,299sf. The height restriction reduces the buildable buildable square footage and therefore the value of the site as well by 47%. Without sliver law, the site may sell at $3,300,000 assuming it is transacted of the same $/ZFA. 

The maximum height of the building may be exceeded if the building abuts an existing adjacent building that is taller than the permitted height. On a wide street with two abutting buildings exceeding the permitted height, the maximum height of the new development may reach the tallest of such two abutting buildings. For example, a lot fronts an 80-foot-wide street with two adjacent abutting building with heights of 100 and 120 feet, respectively. Under normal circumstances, the maximum building height would be 80 feet, or 8 stories. Since the two abutting buildings are taller than 80 feet, the maximum height may reach the taller of the two: that is 120 feet, or 12 stories. On a narrow street with two abutting buildings which exceed the permitted height, the maximum height may reach the lowest of such two abutting buildings. For example, a lot fronts a 70-foot-wide street with two adjacent abutting buildings with heights of 90 and 80 feet, respectively. Under normal circumstances, the maximum building height would be 70 feet, or 7 stories. Since the two abutting buildings are taller than 70 feet, the maximum height may reach the shorter of the two: that is 80 feet, or 8 stories. 

On the other hand, sliver law does not apply to denser commercial districts, such as C4-2F, C4-4, C4-5, C4-6, C4-7, C5 or C6 districts, with an exception only to quality housing buildings despite the residential equivalence of R7 to R10 (as per ZR 35-23(a)). For example, the maximum building height of a development on a 40-foot-wide lot fronting a 70-foot-wide street may exceed the typical maximum height of 70 feet if the parcel is located in a C6-3 zone, with R9 residential equivalent.. If the zoning was C6-3A (R9A equivalent), sliver law would apply, since quality housing buildings are mandatory in this district. Additionally, new development can cantilever and make an easement agreement to the adjacent properties in order exceed the sliver law maximum building height. Normally, a development on a 40-foot-wide lot fronting a 60-foot-wide street could only reach a maximum building height of 60 feet. However, above the height of 60 feet, the new development can cantilever 5 more feet creating a total of 45 feet of street wall. This way, the new development with the easement can exceed the height of 60 feet because the minimum street wall requirement is fulfilled. Lastly, corner lots in R7 to R8 districts have an advantage over interior lots because of differing maximum lot coverage requirements. In these districts, development on corner lots are permitted to have 100% lot coverage within 100 feet of street intersections, while interior lots can only be built to 65% (R7) and 70% (R8) lot coverage. As a result, corner lots can use more square footage per floor before reaching the maximum building height dictated by sliver law. For example, two 2,500 sf of interior and corner lot is zoned in R8 district fronting the same 70 feet street width. With a maximum allowable building height of 70 feet or 7 stories, the interior lot can only build 4.9 FAR or 12,250 sf (70% lot coverage multiplied by 7 stories) while the corner lot can build up to the maximum FAR of 6.02 or 15,050 sf by just building 6 stories with the allowable 100% lot coverage.