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The original item was published from 2/1/2021 11:21:45 AM to 2/1/2021 11:21:45 AM.

Town News


Posted on: January 10, 2020

[ARCHIVED] County Council Adopts New Rules for Accessory Dwelling Units

The County recently made substantial changes to the rules governing accessory dwelling units (ADUs).  These changes set forth in Zoning Text Amendment 19-01 (ZTA 19-01) “Accessory Residential Uses – Accessory Apartments” and companion Bill 22-19 Accessory Dwelling Units – Licensing Requirements Amendments went into effect on December 31, 2019.  The following material explains what an ADU is, what the new County rules for ADUs are, and rules for ADUs in the Town.

What is an ADU? 

An ADU is a second dwelling unit located on a lot with a single-family house.  An ADU is subordinate to the house.  An attached ADU is one that is located inside the house, often in the basement.  A detached ADU is one that is in an accessory building in a rear yard (e.g., a converted garage, a “tiny” house, a granny pod, a prefabricated unit).

What problem is ZTA 19-01 trying to solve?
County Council member Hans Riemer introduced ZTA 19-01 to encourage the creation of more ADUs in single-family neighborhoods throughout the county. Proponents of the ZTA see ADUs as a means of producing additional housing options, whether for extended families or as a source of supplemental income.  ADUs are also seen as a means of increasing the supply of affordable housing, though there are no provisions in the ZTA to ensure affordability.

What are the County’s rules for ADUs as of December 31, 2019?

County Rules for both Attached and Detached ADUs:

  • One ADU, either attached or detached, is allowed per lot
  • All ADUs must be licensed by the County. There will be no annual licensing fee for an ADU occupied by an individual with disabilities
  • To obtain a license for an ADU, the property owner must live either in the house or in the ADU.
  • A property with a licensed ADU cannot also get a license for short-term rentals (e.g., AirB&B). After having an ADU for one year, the ADU license could be dropped and a license for a short-term rental unit obtained. If that is done, the stove would have to be removed from the kitchen of the unit. Rentals of 30 days or less are considered to be short term.
  • A maximum of two adults can live in the ADU (the number of children allowed is regulated by county housing rules).
  • No off-street parking spaces are required for ADUs in the Town because all lots are within a mile of Metro or Purple Line stations.

Additional County Rules for Attached ADUs

  • In most cases the size of an attached ADU is limited to 1,200 square feet. An attached ADU located in the basement/cellar of a house can be larger than 1,200 square feet if the basement or/cellar is larger than 1,200 square feet.
  • The door for an attached ADU must be on the side or rear of the house, unless a second door already exists on the front of the house, or the house and ADU share an entrance.
  • Minimum Ceiling Hight: At least half of the floor area of every habitable room must have a ceiling height of at least 6 feet 8 inches, except that obstructions (beams, girders, ducts, etc.) may project to within 6 feet 4 inches of the finished floor.

Additional County Rules for Detached ADUs

  • The size of a detached ADU is limited to the least of:
  • 50% of the footprint of the house;
  • 10% of the lot area; or
  • 1,200 square feet of gross floor area.
  • The maximum height of a detached ADU is 20 feet. (Note that the Town does not allow the height of an accessory building to exceed 15 feet.)
  • There is no setback requirements for a detached ADU located in an accessory building built before May 31, 2012. If an existing building is enlarged (e.g., footprint or height changed), then it is considered to be a new building and setbacks required for a new detached ADU apply.
  • A detached ADU located in an accessory building built after May 30, 2012, must have a side setback at least as great as that required for a house and a rear setback of at least 12 feet. A larger setback is required for detached ADUs with a wall-length greater than 24 feet (an extra foot of setback for each foot of wall length over 24 feet). The County also requires a larger setback if the ADU is taller than 15 feet (note that the Town does not allow accessory buildings to be taller than 15 feet).
  • The County’s lot coverage rules apply to detached ADUs.
  • If the ADU is closer to the side property line than a house is allowed to be, no new windows can be put in the wall on that side.

ADUs in the Town

What was the Town’s position on ZTA 19-01?

The Town Council, assisted by the Land Use Committee, kept up with each phase of ZTA 19-01’s progress. Mayor Barney Rush testified for the Town at the Planning Board’s February 14, 2019 hearing and Council member Joel Rubin testified for the Town at the County Council’s February 26, 2019 public hearing. They conveyed the Town’s support for most of the ZTA’s provisions. 

The Town also expressed the position that size limits should be retained on ADUs and that existing accessory buildings converted to detached ADUs should not be exempt from setbacks. Following the County Council’s June 2019 work session, the Town sent a letter expressing support for several of the changes made to the proposed ZTA arising from the work session review.   The letter specifically referenced the Town’s support for the following modifications to the initial draft ZTA:

  1. retention, in most instances, of, the 1,200 square foot cap on the size of an ADU, and
  2. retention of the requirement that, in most instances, an attached ADU must have a separate entrance at the side or the rear of the primary dwelling.  

The Town again requested that existing accessory buildings converted to detached ADUS not be exempt from setbacks.  Read the letter. 

Can the Town regulate ADUs?

Yes, to some extent. The Town has the authority to regulate the setbacks, height, and mass of buildings in the Town, the amount of impervious surfaces, stormwater runoff, tree removal, and parking. The Town’s rules can be more restrictive, but not less restrictive than the County’s rules. Thus, the Town can regulate some aspects of an addition to a house used for an attached ADU and of an accessory building used for a detached ADU.

If the Town does not change its current rules for accessory buildings, what could happen with detached ADUs in the Town?

Under current Town and County rules, a detached garage built before May 31, 2012 can be converted to an ADU without regard to setbacks (older garages often sit on or very close to the side and/or rear property lines). If the building does not meet the setbacks required for new ADUs, the building’s footprint cannot be enlarged, its height cannot be changed, and no new windows can be put in the side nearest the property line.

The Town and County rules regarding a new building constructed for a detached ADU include the following:

  • It must be located in the rear yard and occupy no more than 25% of the rear yard;
  • It must be located at least 12 feet from the rear property line;
  • It must have at least the same side setbacks as currently required for a house;
  • Its rear and side setbacks may be increased depending on the building’s wall length and height.
  • It must have a height of 12 feet or less if it has a flat roof or 15 feet or less for other roof types.
  • Its gross floor area will have to conform to the county’s size limits for detached ADUs set forth above. In addition, its gross floor area will be limited by the County’s lot coverage rules, and by the Town’s Floor Area Ratio rules
  • The Town’s stormwater rules will apply if the ADU’s footprint is 700 or more square feet.
  • The Town tree canopy rules will also apply.

Proposed Changes to Town Rules Governing Detached ADUs

The proposed rules follow the position taken by the Town during the ZTA 19-01 process. Briefly, the proposed rules would require that an accessory building used for an ADU meet the Town’s side and rear setback requirements for a house, with some additional setback requirements for buildings exceeding specified lengths and heights. The Town is not proposing to adopt any additional rules about attached ADUs or about parking for attached or detached ADUs.

The Town’s position on setbacks for detached ADUs does not prevent someone from having an ADU.  A resident interested in developing a non-conforming detached ADU could seek a variance, and, in any event, could build an attached ADU.

What You Can Do

  • Send your comments to the Town Council at
  • On February 19 at 6 p.m. the Town Council will hold a work session to discuss regulating ADUs in Town.  Residents are welcome to attend the work session but will not be able to participate in the discussion.  If the ordinance is introduced at the February meeting, the Council will then hold a public hearing on the proposed rules at a future meeting.

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