PLANNING TOOLKIT

ACCESSORY DWELLING UNITS

INTRODUCTION

An accessory dwelling unit (ADU) is an additional living space located on the same property as an original, larger residence.

They’re often called by other names: granny flats, mother-in-law units, casitas, ECHO units and dozens of others.

ADUs can offer affordable accommodation to elderly relatives or children returning home, or they can be rented out to contribute toward mortgages and other associated housing costs.

The concept isn’t new; it was a common housing option for multi-generational families and for returning soldiers after WWII. But with the growth of the suburbs and the dominance of single-family zoning, ADUs were often prohibited.

Today, however, more communities are allowing ADUs as a way to solve local housing availability and affordability issues -- a problem that has become a national crisis.

ADUs can take many forms, but the three basic types are interior, attached and detached:

An interior ADU utilizes existing space within the primary dwelling through the conversion of an interior room such as an attic or basement.
An attached ADU is added to the front, side or rear of the primary structure, or often constructed above an attached garage.
A detached ADU is structurally separate from the primary dwelling. It can be built as a stand-alone unit or added to an existing structure such as a detached garage.

Although ADUs are usually smaller than the primary residence, they often contain the same essential amenities such as a kitchen, bathroom, living room or bedroom, depending on the available space and intended use.

BENEFITS

Allows elderly to age in place;
Close help for child rearing and/or elder care;
Affordable housing options;
Housing options for workforce, especially in communities facing labor issues;
Additional income to support principal residence.

DRAWBACKS

The property owner may have difficulty subdividing the two dwelling units in the future;
Developers may create additional units as investment opportunities instead of providing additional housing options at an affordable price;
Sharing of electric, water, sanitary and storm sewer systems;
Construction must assure access by emergency services;
Possible of limited parking availability;
Compatibility of design with the existing

neighborhood;
Adequate infrastructure to support another dwelling unit;
Tax clarification for more than one residence on a single lot.

RESOURCES

TCRPC Accessory Use Model Ordinance
Lebanon County Resources
Chester County Resources
General ADU Guidelines
AIA Practices

RELATED FACT SHEETS

Form Based Codes
Tiny Houses

TIPS TO CONSIDER

Consider public outreach to address concern that ADUs will alter community character;
Consider allowance through special use permit;
Allow ADUs as a use by right, reducing time and lowering cost;
Allowance by right doesn’t preclude municipality creating controls and conditions;
Consider allowing ADUs in certain neighborhoods to determine effectiveness.