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Posted on: May 8, 2019

County Council to Adopt New Rules for Accessory Dwelling Units

The Montgomery County Council will vote this summer on substantial changes to the rules that govern “accessory dwelling units” (ADUs) (Zoning Text Amendment 19-01).  An ADU is a separate dwelling unit located on a lot with a single-family 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 garage, a “tiny” house, a granny pod).

The most significant change in the rules for ADUs is that, for the first time, detached ADUs will be allowed in residential neighborhoods like the town (zoned R-60). Under the proposed county rules, detached ADUs could have minimal or no setbacks from side and rear property lines.  The Town can adopt rules to govern detached ADU setbacks and screening.  But before considering any measures, we would like to hear views from residents on this matter.  Please write to the Town Office if you have interest or questions.  

What will the County’s ADU rules be?

•    There can be one ADU (attached or detached) per lot.

•    The property owner must live either in the house or in the ADU.  

•    A property with a licensed ADU cannot get a license for short-term rentals (e.g., AirB&B).  

•    Two adults can live in the ADU (the number of children is regulated by county housing rules).  

•    No off-street parking spaces will be required for ADUs in the Town because all lots are within a mile of Metro or Purple Line stations.

•    The size of an attached ADU will be limited to 1,200 square feet or 50% of the gross floor area of the house, whichever is less.  An attached ADU can be larger than 1,200 square feet if it is located in the basement of a house. 

•    The size of a detached ADU is limited to 10 percent of the lot size or 1,200 square feet, whichever is less.

•    There are no setback requirements for a detached ADU located in an accessory building built before June 1, 2012.

•    An ADU located in an accessory building built after May 31, 2012, must be setback at least 5 feet from the rear and side lot lines.  The County requires a larger setback for detached ADUs with a wall-length greater than 32 feet (note that the County requires larger setbacks for other types of  accessory buildings when their wall lengths exceed 24 feet)

•    There are no screening requirements for detached ADUs, though if the ADU is less than 5 feet from the property line, no new window can be put in the wall on that side.

Detached ADUs in the Town

•    Detached garages in the Town built before June 1, 2012 could be converted to ADUs without regard to setbacks.  Older garages often sit on or very close to the side and/or rear property lines.

•    An existing detached rear yard garage built after May 31, 2012 could be used for a detached ADU provided it meets County setback requirements, see above. 

•    A new accessory building could be built in a rear yard for a detached ADU (e.g., a tiny house or granny pod).  If a new building is constructed for the detached ADU it would have to meet County and Town setback and height requirements and could occupy no more than 25% of the rear yard.  The gross floor area of the ADU building could be limited by the maximum Floor Area Ratio for the lot.

Topics to Consider

•    Should the Town regulate the setbacks of a detached ADU located in an accessory building built before June 1, 2012?

•    Should the Town require the same setbacks for a detached ADU as it requires for other accessory buildings (e.g., garages, sheds), or should the setbacks for a detached ADU be greater than those for “passive” accessory buildings?

•    Should the Town require screening for a detached ADU?

More information

For more information, see the fact sheet. 

What You Can Do

Send your comments to the Town Council at townoffice@townofchevychase.org .

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