Net-Zero in the New Year – On the Boards


We have an exciting project on the boards. We are designing a Net-Zero passive solar Accessory Dwelling Unit (ADU) in NE Portland.  We plan to host a ‘lunch-and-learn’ on the subject of Net-Zero design and Accessory Dwelling Units in the near future. Please contact us (info@holahdesign.com) if this is something you’d like to attend!

There has been quite an interest lately in designing Accessory Dwelling Units (ADU). We thought we would provide a bit more on the subject. Often referred to as a ‘mother-in-law unit’ or a ‘granny flat’, an Accessory Dwelling Unit (ADU) is (essentially) an additional dwelling unit created on an existing lot with a house, attached house or manufactured home. The second unit is created auxiliary to, and is smaller than, the main dwelling unit. It is a compact living unit that includes, but isn’t limited to a bedroom, bathroom and kitchen. In the City of Portland, ADU’s are not duplexes and are only allowed on zoned residential lots. ADU’s can be created in a variety of ways, including the conversion of a portion of an existing house (i.e. basement or attic), an addition to an existing house, or a entirely detached structure. This often includes the conversion of an existing garage or the construction of an entirely new building.

Development of accessory dwelling units (ADU’s) can be traced back to the early 20th century when they were a common feature in single-family housing. Portland has been a leader in the effort to emphasize density and minimize urban sprawl by focusing on the Urban Growth Boundary (UGB). ADU’s have emerged as an important housing solution based on the planning principal to create housing development that is high-density, transit-oriented, mixed-use and mixed-income through urban infill design.

In 1998, the City of Portland began to actively encourage the development of the ADU. However, the SDC (System Development Charges) fees involved became a cost prohibitive, sometimes as high as $15,000 in addition to construction costs. Recognizing that development of the ADU was scarce, in April 2010, the City of Portland decided to waive most SDC fees until June 30, 2013. This means that most permit fees including those for the Parks, Environmental Services, Water, and Transportation Bureaus are reduced if not waived entirely.

In addition to the reduced fees for construction of an ADU, the City also increased the allowable size of an ADU to 800 square feet. The effort to promote this form of urban infill development within the residential zoning of our City has successfully increased permit submittals at the City and many Architects are seeing an increase in demand for this type of project design.

The City of Portland states in its Planning Code that the purpose for allowing the development of the ADU is to:

Create new housing units while respecting the look and scale of single-dwelling development.

Increase the housing stock…in a manner that is less intense than alternatives.

•Allow more efficient use of existing housing stock and infrastructure.

•Provide a mix of housing that responds to changing family needs and smaller households.

•Provide a means for residents, particularly seniors, single parents, and families with grown children to remain in their homes and neighborhoods and obtain extra income, security, companionship and services.

•Provide a broader range of accessible and more affordable housing.

ADU’s offer a variety of benefits to residential neighborhood communities. Over the last decade, housing needs have changed to include a growing demand for smaller housing types. Single persons, baby boomers, and empty nesters have all contributed to a decline in the average household size. The coincidental increase in the demand for smaller housing types and the existing surplus of housing land/lots has led many communities (like Portland), to emphasize the development of the ADU as an efficient and low cost strategy for increasing affordable housing.

Additionally, the movement for ‘aging in place’ has grown with the high number of aging baby boomers. Elderly and/or disabled persons who may want to live close to family, empty nesters and young adults entering the workforce all find ADU’s to be an desirable housing solution. ADU’s increase housing stock and are an affordable option for varied income residents. Homeowners benefit from added income and because of zoning laws, ADU’s are designed to blend in with the local architecture, which benefits the whole community.

The City has strict design guidelines for the ADU. The ADU must replicate the style of the existing original house. This occurs in roof pitch, siding material, window and trim details, etc. In addition to the design guidelines, there is a procedure that must be followed for the permit process at the City. An Architect can facilitate this process and coordinate both design, fees and construction issues with both the City and the selected contractor.

While the ADU is often seen as a form of housing, it is also a great option for a home office, artist studio or even a guest house for visiting friends and relatives.


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