Accessory Dwelling Units

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Accessory Dwelling Units (ADU): What Are They and Other Frequently Asked Questions

The Board of Trustees is considering a local law that will allow homes in Single-Family Residential Zoning Districts the ability to add one additional smaller dwelling unit within the existing principal structure. Accessory Dwelling Units have also been called a mother-in-law apartment, granny flat or an in-law suite. The legislation is designed to be a low impact approach to increasing the number of housing units in the Village while also providing a way for seniors in our community to age in place. As has been said by the Westchester County Planning Department and housing experts, this is just one tool in the toolbox to make housing more affordable in our region.

Please see below answers to general questions about Accessory Dwelling Units as well as specific questions the Village has received from residents.

What is an Accessory Dwelling Unit? (ADU)

An ADU is a second smaller apartment on the property of an existing home in a Single-Family Residential Zone. The proposed legislation would only permit an ADU in an existing principal structure, not in an accessory structure such as a detached garage or shed. ADUs must include kitchen facilities, a sleeping area, living area and a bathroom, and must adhere to all building code regulations in terms of safety. No more than one ADU would be permitted per lot.

Would owners be required to live on the property?

Yes. The proposed legislation requires the owner to live on the property, as their primary residence, in either unit.

How would the Village verify owners live on the property?

The owner would be required to register annually with the Building Department on the Landlord Registry. Proof of primary residence will be required.

Where would ADUs be permitted?

In Single Family Residential Zones (RS-6, RS-9, RS-12, CD - see zoning map ) within the principal structure. ADUs would not be permitted in accessory structures.

Is the proposed ADU legislation going to change all Single-Family Residential Zones to Multi-family zoning districts?

No. The Village Code has separate zoning districts where two-family and multi-family units are allowed. The Accessory Dwelling Unit proposal would only allow one additional smaller accessory dwelling unit per lot, and that unit must be within the single-family structure. Multi-family zones permit more than one additional unit which can be equal in size to other units.

How big could an ADU be?

In the proposed legislation ADUs must be a minimum of 400 sq ft and cannot be larger than 30% of the total useable square footage of the principal structure. 

How many people could live in an ADU? Is there a limit?

The New York State Building Codes limit the number of people who can inhabit a residence based on square footage. The number of people who can reside in a unit is based on the size of the unit.

Is additional parking required?

Yes. An additional off-street parking space is required in addition to 2 off street spaces for the primary residence.  If an attached garage is turned into an ADU, the property is still required to have two spaces on site for the primary residence, and an additional space for the ADU.

Is Planning Board Review required?

If an ADU is constructed within the existing footprint of an existing structure, no site plan review is required. However, a building permit and review from the Building Department to ensure adherence to building code standards for safety including fire codes are ALWAYS required. If the ADU expands the existing footprint or square footage of the existing structure or additional impervious surface must be added to accommodate for off-street parking spaces, Planning Board review may be required if the increase meets the Code’s existing thresholds for any improvement (ADU or otherwise).

My neighbor has a detached garage bordering my property. Could it be turned into an ADU with tenants suddenly staring into my backyard?

No. ADU would not be permitted in an accessory structure. Only permitted in the principal structure.

Is my neighborhood going to be transformed by this legislation?

Based on the experiences of other communities, no. The purpose of the legislation is to offer a low-density and low-impact opportunity to chip away at the housing crisis in our area. It will also offer benefits to existing residents (in terms of additional income) and new residents (in terms of a new unit). The following is data from other Westchester villages that permit Accessory Dwelling Units, the years they were enacted, and the number of units in each community to date (source: Westchester County Planning Department):

  • Briarcliff Manor (2014): 26
  • Buchanan (1989): 25
  • Croton on Hudson (2015): 10
  • Hastings on Hudson (1997): 23
  • Irvington (2016): 2
  • Pleasantville (2020): 5

Other Villages that recently adopted legislation permitting ADUs include Ardsley (2022), Dobbs Ferry (2022) and Tarrytown (2023).

Westchester towns that permit ADUs include Bedford (400), Cortlandt (172), Lewisboro (86), Mount Pleasant (159), New Castle (156), North Castle (85), North Salem (265), Ossining (30), Pound Ridge (28), Somers (30), and Yorktown (177). (Number of ADU’s provided by Town Supervisors.)

Was this legislation considered in our Comprehensive Plan?

No, in 2018 ADUs were not discussed. The Comprehensive Plan identified the need for more workforce and market rate rentals in the Village. The plan focused on specific areas for new development or adaptive reuse including downtown and the Lexington Avenue area. At that time, there was not a plan to modify other residential zones. This zoning change would require an amendment to the Village’s Comprehensive Plan, or an explanation of how the change is consistent with the Comprehensive Plan.

If this legislation is low impact, why should we institute it at all? Don’t we have enough affordable housing in the Village?

The purpose of ADU legislation is to provide an opportunity for those who need it, whether it be to house a family member who needs to move back home, or receive rental income from a second unit in order to age in place. According to the 2019 Housing Needs Assessment for Westchester County, 18% of Mount Kisco households are severely cost-burdened. This means that more than 50% of income goes toward housing costs. This legislation offers one alternative for those who need it.

What happens to the tenant should the property owner(s) die and the property is transferred or sold to a non-resident? How will the village enforce the owner occupant requirement? 

The property owner will have the same responsibilities as any landlord, and the terms of a lease when the property changes hands will apply.

The Building Department’s ability to track principal ownership of an ADU when the property changes hands.  The Building Department will be able to monitor transfer of ownership through their receipt of title search requests. When a title search is received, the Building Department will advise the new owner that they are required to re-register the Accessory Dwelling Unit with the Building Department and provide the regulations surrounding requirement of primary residence.

How will this make the village more affordable?

Accessory Dwelling Units help diversify the range of housing options available. Housing affordability is connected to supply and demand. By increasing the supply of housing, it helps control rental rates. Accessory Dwelling Units are by nature small, and therefore more affordable than larger units. To be clear, ADUs will not “solve” the affordable housing crisis we are experiencing. It can however have a positive an impact.

What about reducing taxes to increase affordability?

Village taxes only account for 25-30% of the property tax burden. The majority of property taxes go to the school district. Nevertheless, the Village continues to make efforts to keep the tax levy steady while delivering the level of service expected by residents. To be clear, however, expanding the Village’s tax base in ways that don’t place significant burdens on existing resources is also a way to reduce taxes.

If the goal is to create affordable housing how does the village plan to regulate rent?

The legislation is intended to increase the availability of smaller more affordable housing units in the Village, and it is also meant to help residents age in place instead of having to leave the Village after they retire. The Village does not regulate rents. It will be up to the homeowner and the market to set the rental price. But the small nature of the units and the increase in supply should help keep rental rates in check.  If a resident needs to access government subsidy to build out a unit, then the unit will come with a government requirement to rent at an affordable rate.  The owner of the property will be governed by the subsidy provider to maintain affordability. 

Will the addition of an ADU be considered an improvement that will increase the valuation of the property thereby increasing the owner’s property tax rate?

Yes. Improvements made to a home including the addition of an accessory dwelling unit will likely increase the assessed property value of the home.

Does the village anticipate additional tax revenue?

If the assessed property value of a home increases with the addition of an Accessory Dwelling Unit, then tax revenue may slightly increase which will help accommodate additional residents.

Does the village anticipate demand for ADUs in Mount Kisco from neighboring communities?

The demand for ADUs will likely be the same as any rental apartment. Neighboring communities (i.e. Bedford, New Castle and North Castle) currently permit ADUs.

Has the demand for market-based housing diminished? Is the Village only focused on affordable housing?

No. Proposals for the development of private property for market-based housing will continue to come before the Planning Board and will be and will considered based on zoning and SEQRA review. The demand for housing across the region is incredibly strong and New York State is behind in providing new units to keep up with demand.

How many properties in the village currently meet the eligibility requirements set forth in the legislation?

Accessory Dwelling Units would be permitted in single family residential zones. Full build-out, meaning if every single-family home added an ADU, would be 908 additional units. A more realistic estimate, based on the number of ADU’s in other communities is less than 10% of the eligible properties.

What is the tenant application process and how will the Village ensure adherence to fair housing practices? 

The Village does not get involved with adherence to fair housing practices for other rental units, and nor will it do so in the case of ADUs. If there is a complaint regarding fair housing practices, it is handled by the Westchester County Human Rights Commission.

Can an existing multiple-family home add an ADU?

No. The proposed code only permits single-family homes in single-family zones to add an ADU. Multi-family home cannot add an ADU.

Will there be a revolving door of tenants, or AirBnB guests in and out of my neighborhood?

No. The legislation indicates Accessory Dwelling Unit “shall not be utilized on a transient or short-term basis of no less than 6 months. Occupancy shall be restricted to full-time residency.”

Can an attached garage become an ADU?

Yes, if off-street parking requirements are met. Two off-street parking spaces are required for a single-family residence. One additional off-street space will be required for an ADU. If the garage provides the existing parking spaces, then the application will require a Planning Board site plan review to ensure the parking requirements are met.

Is the village going to allow applications for variances for ADU's that don't align with the proposed legislation?

The ADU legislation will be in the newly created Chapter 40 of our code. Since it is not part of our Zoning Code, it will not be subject to review for a zoning variance. For example, the ADU must be within the principal structure. The property owner cannot seek a variance to put an ADU in an accessory structure. The property owner can, however, seek a variance from the zoning requirements of the district where the building is located.

How will you measure success of the program?

The program will be considered a success if units are added to the supply of housing in the village. In addition, if illegal apartments are made legal, and compliant with building codes and safety regulations, the program will be deemed a success.