Accessory Dwelling Units (ADU's) are becoming more and more a part of the traditional American home. Homeowners love the idea of having an additional small accessory structure that functions as a work-from-home office or a detached apartment for an aging relative. Their relatively small footprint makes them an economical way to add value to your existing home.
Figure (a) ADA compliant ADU floor plan (938 sq. ft.)
What is an ADU?
An ADU is a small, typically detached structure that is accessory to the primary residence. Situated on the same lot as the principal building, the ADU allows homeowners to build an additional structure that complies with the local zoning and building codes. Before the advent of the ADU, typical accessory structures on a residential lot would be limited to more utilitarian structures like garages and sheds.
The Philadelphia Zoning Code Chapter 14-404 (11) (a) (.1) describes an ADU as "providing a means for residents—particularly seniors, single parents, and empty-nesters—to remain in their homes and neighborhoods, and obtain extra income, security, companionship, and assistance; and accommodating a broader range of accessible and more affordable housing." [1]
Some cited benefits of allowing this building typology include increased housing affordability and creating a wider range of housing options for neighborhoods. [2] In addition, younger families with aging relatives have the option to live together while maintaining their privacy and individuality.
Limitations_
Your local building department will outline the requirements and limitations of the accessory structure. Often there will be rules on site placement, setback, overall square footage and height, usage, etc. In Philadelphia, the ADU is limited to 800 sq. ft., and the principal dwelling on the property must be occupied by the owner of the property. This would prevent a landlord who does not live at the property from adding an ADU to their rental property and increasing the number of available units.
Typologies_
ADUs can be designed as compact apartments featuring a bedroom, full bathroom, kitchen, and living area. Some homeowners are creating their units to serve as home offices or versatile open spaces for hosting garden parties. Because an ADU can have all primary functions on a single floor, it is important to consider implementing universal design principles. The ADU shown above (figure a) was designed with ADA compliance in mind and allows an occupant with mobility issues to live comfortably. Below (figure b) is a non-ADA compliant ADU floor plan which is efficient and compact.
Figure (b) ADU floor plan (760 sq. ft.)
Challenges_
Some challenges to consider when planning your ADU with your architect and builder are as follows:
Electrical service. It can be costly to run an underground service line, so the building location relative to the closest connection should be considered.
Plumbing service. If you are including a bathroom in your ADU plan, keep in mind that new supply and waste water lines will need to be accounted for in the budget.
Heating and cooling strategies. For a small structure like an ADU, mini-split air conditioners seem to make the most sense, no need for a traditional air handler and branch ducting. Some clients install radiant heat in the floor for a more even distribution of heat. With the relatively small size of these structures, it's good practice to pay close attention to the energy efficiency of the home to reduce future utility bills.
References_
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