Starting the Permit Process

Shrinking family size isn’t just an anomaly in the United States, it’s a trend. One implication of smaller families is housing requirements. Before, houses needed to be built to accommodate over five people. Now, that number is decreasing to four, and often times is just two as couples continue to postpone forming a family. So, if a family doesn’t need all the extra room provided by existing homes on the market, what can be done?

One common solution is for current home owners to build what is called an Accessory Dwelling Unit on their property (easier said as ADU), then rent this property out. There is a process involved in permitting an ADU. This article aims to demystify that process for anyone interested in adding an ADU to their property, particularly for those in the Portland metro area.

ADU for hardship purposes

What Exactly is an ADU?

An ADU is a secondary housing unit that is built on a residential lot meant for a single family. At a time when terms such as tiny home, granny flat and backyard cottage are becoming increasingly common it can be hard to understand the difference. It is important to note that it is not the structural form itself that defines an ADU, but its purpose. Given that an ADU’s purpose is to serve as a residence, it must possess facilities for sleeping, cooking, and sanitation.

So long as such facilities are provided, an ADU can take many structural forms, including garage conversions, basement conversions, additions to an existing house, and can even be built as a detachment from the primary residence.

Downtown City of Portland

What are the requirements to having an ADU?

In order for you to install an ADU on a site in Portland, there is a list requirements that need to be met. The ones provided here are necessary to consider before applying for an ADU permit, but note that as with any residential structure there are also building codes that must be followed for ADU’s. Those are not provided here but can be found on the Portland Government’s website.

  • General requirements: An ADU is allowed on properties that are zone Residential, Commercial, and Central Employment. They should be created as an accessory to an onsite residence as a detached unit, an addition to the present house or manufactured house. There can be no more than one ADU on any property.
  • Number of residents: The number of residents allowed in an ADU is limited by the total number allowed in one household. Your household can have any number of blood-related relatives living in it and up to five non-related members. So, if the occupants of the ADU are related by blood to the you, the owner of the primary residence, the number of people allowed is unlimited. If they are not related to the you, then the number allowed is limited to five unless there are unrelated residents already living with you in the primary residence.
  • Size: All ADU’s must be smaller than the primary residence. Specifically, the living area of the ADU must either be 75% smaller than the living area of the primary residence or 800 square feet- whichever is less.
  • Entrances: Only one main entrance can be on the street-facing side of the house. Detached units are exempt from this rule.
  • Parking: Additional parking for the ADU is not required. But it is important to note that any onsite parking available for the primary residence must either be left or replaced.

Detached ADU Requirements

If you plan on building a detached ADU there are additional requirements to be met. If the ADU is detached from the primary residence it must meet all previously listed requirements, plus meet the following:

  • Height: a detached ADU must not exceed 20 feet.
  • Building coverage: the ADU’s coverage must not exceed the coverage of the primary. residence. Further, the ADU cannot take cover more than 15% of the total site area.
  • Location: The ADU must either be set back 40 feet from the front lot line or be behind the rear wall of the primary residence.
  • Exterior detail: for an ADU that is 15 feet of higher, the finish materials, and roof pitch, trim, eaves, window orientation and dimension must matched that of the primary residence, or must be made of wood, composite boards, vinyl, or aluminum products composed in a shingle pattern or in a horizontal clapboard or shiplap pattern with boards that are six inches wide or less.

installing adu in backyard

Getting a Permit for ADU’s

If you find that the requirements listed above can be satisfied on your property, there is a permit application process go through. Below is a list of forms that must be filled out along with other documents that need to be provided:

  • A completed Building Permit Application form.
  • A Residential System Development Charge form.
  • If applying to add a detached ADU, you must submit a completed NSFR Intake Packet.
  • Site and building construction plans.
  • Erosion control plan or a completed simple site erosion control form (if project include ground disturbing activity).
  • Mitigation for and/or a storm water plan if the proposed unit will cover more than 500 square feet of impervious area.

If you plan on building a detached ADU there are additional requirements to be met. If the ADU is detached from the primary residence it must meet all previously listed requirements, plus meet the following:

To acquire a permit for an ADU, you must bring all of these forms and four copies of site, architectural, and structural plans (for the area of proposed work and areas affected by such work), plus the required intake fees must be brought to the Development Services Center.

An Accessory Dwelling Unit can be a beneficial structure to have on your property whether its purpose is to provide for more room for your family or add extra income to your household. While the process to acquiring can be a daunting task, hopefully this article has made it a little less so. For additional information on beyond the permit process check out our article on tiny houses in Portland. It discusses in detail how to better approach decision making when it comes to ADUs, as well as some thing to consider when funding your home.