What it costs to build an ADU in Mamaroneck, NY

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 2,100 sq ft for one story, 1,800 sq ft for one and one-half, and 1,500 sq ft for two or two and one-half.
• Each side yard is at least 35 ft.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 2,100 sq ft for one story, 1,800 sq ft for one and one-half, and 1,500 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 1,400 sq ft for one story, 1,100 sq ft for one and one-half, and 900 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 1,600 sq ft for one story, 1,300 sq ft for one and one-half, and 1,000 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 1,900 sq ft for one story, 1,700 sq ft for one and one-half, and 1,400 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

Two-Family Residence District - The code sets no lot minimum here: each dwelling unit needs 5,000 sq ft of lot area and 50 ft of lot width and street-line frontage. A lot held in single and separate ownership on June 29, 1959 with at least 7,500 sq ft may be used for a two-family residence.

• Total floor area follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if greater, never more than 15,000 sq ft.
• One-family and two-family dwellings are both principal uses.
• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 1,000 sq ft for one story, 800 sq ft for one and one-half, and 700 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 1,000 sq ft for one story, 800 sq ft for one and one-half, and 700 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

One-Family Residence District - Total floor area of all buildings on a one- or two-family lot follows a chart by lot size, 0.55 up to 6,000 sq ft and falling as the lot grows, or the average of the neighbouring comparison parcels if that is greater, and never more than 15,000 sq ft.

• The 35% coverage cap counts buildings, accessory structures, pools, courts, drives and paved areas together, and there is no separate building coverage cap.
• Minimum first-floor area is 1,200 sq ft for one story, 1,000 sq ft for one and one-half, and 800 sq ft for two or two and one-half.
• Usable open space of 1,200 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

Garden Apartment District - The code sets no lot minimum and no lot width here, only 3,500 sq ft of lot area per dwelling unit and a lot depth of at least 150 ft.

• Floor area must average at least 750 sq ft per dwelling unit.
• The 25% cap is building coverage, the share of the lot covered by buildings.
• Principal uses are dwellings for more than two families, plus the one- and two-family dwellings permitted in R-2F.
• Usable open space of 400 sq ft per dwelling unit is required.
• A corner lot needs a front yard on each street and a rear yard, and the owner chooses which yard is the rear.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

Attached Residence District - Each dwelling unit needs at least 2,500 sq ft of lot. The 25 ft side yard, for one side and combined, applies to a lot with only one interior lot line; a lot with two interior lot lines needs no side yard (§ 240-42B).

• Floor area must average at least 750 sq ft per dwelling unit.
• The 35% cap is building coverage.
• Principal uses are the same as R-GA: dwellings for more than two families and one- and two-family dwellings.
• Usable open space of 300 sq ft per dwelling unit is required.
• No lot minimum and no lot width are set, and a lot must be at least 100 ft deep.
• An unattached accessory building on the rear 1/3 of the lot, not over one story or 15 ft, may sit as close as 5 ft to the property line, but on a corner lot no nearer the street than the front yard.

Tower Apartment District - Side and rear yards grow with building height, so the 5 ft side and 15 ft rear figures shown bind only on a short building: a side yard is 1.5 inches per foot of height and a rear yard 3 inches per foot (§ 240-43B).

• A side yard must be at least 10 ft from a street.
• A side yard must also be at least 1 inch per foot of building length.
• Floor area must average at least 750 sq ft per dwelling unit.
• The 20% cap is building coverage.
• Principal uses are those of R-GA plus a professional office.
• Usable open space of 200 sq ft per dwelling unit is required.

Business-Mixed Use Business District - The only dimensional standards the code prints here are for a mixed-use development, which needs a zoning amendment and a special permit from the Town Board on a site of at least 80,000 sq ft, with 7 floors and 87 ft and 60% building coverage.

• The mixed-use standards are a 0.16 nonresidential floor area ratio excluding structured parking, 595 sq ft of gross site area per dwelling unit, and every setback at least 10 ft.
• Buildings must be at least 120 ft from Madison Avenue for a commercial use and 170 ft for a residential use, and at least 15 ft from any other public street.
• No more than one three-bedroom unit per 25 units, and at least one workforce housing unit per 17 units.
• No residential use may sit on the ground floor or below a nonresidential use, except one maintenance apartment, and nonresidential uses may take no more than 40% of the gross floor area.
• Buildings over 30 ft may cover no more than 40% of the site in horizontal cross section, and required front yards are landscaped, not paved.
• Lot, yard, floor area and height standards are set by reference to a Business (B) District that the code no longer contains.

Light Industrial District - No minimum lot area, lot width, front yard, side yard or rear yard is required, but a side yard that is provided must be at least 4 ft.

• Where the lot adjoins a residence district the side yard must be at least 10 ft and the rear yard at least 25 ft, with at least 10 ft of the rear yard planted with evergreens as a screen.
• A corner lot next to a residence district needs a 5 ft setback from the street on which that district fronts.
• Floor area may run up to 100% of the lot area.
• All storage except vehicle parking must be inside a building.

Business-Residential District - The figures shown are for a nonresidential use. A residential use, or a combination of business and residential use, needs a 10,000 sq ft lot, a 15 ft front yard, a 10 ft side yard and a 20 ft rear yard, floor area of 70% of the lot area, and 4 stories and 44 ft.

• No building coverage cap applies to a residential or mixed-use development, and it needs 100 sq ft of usable open space per dwelling unit.
• The side yard drops to 5 ft where the lot adjoins a driveway or parking area.
• On Myrtle Boulevard the Planning Board may reduce or waive the 15 ft front yard and then raise the rear yard to as much as 30 ft.
• A residential development of 10 or more units must make at least 10% of its units Fair and Affordable Housing units, and one of 5 to 9 units at least one.
• For a nonresidential use, a side yard that is provided must be at least 4 ft, and next to a residence district the side yard must be at least 10 ft and the rear yard at least 25 ft.
• No parking may sit in front of a building set back less than 75 ft from the street line.

Service Business-Residential District - The figures shown are for a nonresidential use. Multifamily housing is a special use here: a residential use, or a combination of business and residential use, needs a 10,000 sq ft lot, a 15 ft front yard, a 10 ft side yard and a 20 ft rear yard, with 4 stories and 44 ft.

• Floor area may run to 70% of the lot area for a residential or mixed use, against 50% for a nonresidential use.
• No building coverage cap is set for the district.
• The side yard drops to 5 ft where the lot adjoins a driveway or parking area.
• On Myrtle Boulevard the Planning Board may reduce or waive the 15 ft front yard and then raise the rear yard to as much as 30 ft.
• For a nonresidential use, a side yard that is provided must be at least 4 ft, and next to a residence district the side yard must be at least 10 ft and the rear yard at least 25 ft.
• A residential or mixed use needs 100 sq ft of usable open space per dwelling unit.

Urban Renewal District - The figures shown are the affordable multifamily row, for sites designated on the Zoning Map where every unit meets the Town Board definition of affordable units. An adopted urban renewal plan may instead permit a business use, or multifamily at the R-TA standards.

• Multifamily dwellings allowed under an urban renewal plan at the Tower Apartment (R-TA) standards are capped at four stories and 44 ft, with at least 1,750 sq ft of lot area per dwelling unit.
• A business use permitted by an urban renewal plan takes 150 ft of lot width, 25% building coverage, a 0.5 floor area ratio, and 2 stories and 30 ft.
• For that business use no front, side or rear yard is required, but next to a residence district the side yard must be at least 10 ft and the rear yard at least 25 ft.
• A 5 ft landscaped buffer strip runs along all public streets, broken only for driveways and sidewalks.
• The average unit may have no more than two bedrooms, and no unit more than three.
• Usable open space of 100 sq ft per dwelling unit is required, and side yards are 10 ft each.

Recreation District - A perimeter buffer at least 40 ft wide is required around the whole property, and no principal or accessory use may sit in the required front yard.

• An accessory use needs only 40 ft on the side or rear, not the principal-use side and rear yards shown.
• Principal buildings may cover no more than 1% of the lot, and all buildings together no more than 1.25%.
• No court, pool, green, fairway, tee or structure may be placed in the buffer.
• At least 20% of the parcel must stay permanent open space in its natural state.
• No construction may take place on slopes over 25%.
• No parking is allowed in any required front yard.