Portland Accessory Dwelling Unit (ADU) Permitting Lessons Learned

Having designed many Portland ADUs (Accessory Dwelling Units) over the past couple years and working through the often complex and picky city permitting process, we have some lessons learned on how to best prepare drawings and make decisions early that can make permitting smoother. Below are some of the common questions or issues that arise while permitting an ADU. The earlier we can address these sorts of issues in the design process the easier it is to breeze through the permitting process and start construction on your project.

Energy Efficiency Measures Checklist

Every new project in Portland has to address sustainability in some way. For residential projects, including ADUs, there is a checklist that city asks you to fill out, demonstrating what strategies you are using to reduce energy and water consumption. This ranges from the amount of Wall and roof Insulation, type of Heating Systems, use of low energy LED lighting fixtures, and more. For the ADUs that we have been designing we have focused on some simple strategies that are beneficial for the performance of the building but also easily attainable within our client's budgets.

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Windows vs Doors

The proportions of windows are regulated in the ADU code, requiring them to match those in the existing house. However, many of our clients request bright, open, modern spaces that connect to the outdoors. With many craftsman bungalows or mid century houses, windows were relatively small and almost always vertically oriented, limiting what we can do in the ADU. We have often received comments from the city regarding window proportions and asking for proof that we were matching the existing house. There are two ways to address the discrepancy between what the city will allow and what our clients want.

The first trick is that if you make alterations to the main house you can then match those in the ADU. For instance, if you want a large horizontal window that frames a beautiful view into the garden in your ADU, then you can have your architect also propose adding a similar window somewhere on the main house. We recently did this for an ADU project, where we have a large array of south facing windows on the ADU and in order to accomplish this proposed that the owner also install a similar set of windows in the living room of his main house.


The second work around is that nowhere in the code does the city regulate doors. To create rooms that have a strong connection to the outdoors, we have used glass sliding doors, french doors and accordion doors to create walls of glass, providing beautiful views outside and also rooms that completely open up. This allows us the design flexibility to meet both our clients' wants with the regulations imposed by the Portland ADU zoning code. In this ADU we have wall to wall sliding glass doors opening the living room up to the backyard: http://www.propelstudio.com/project/northwest-modern-adu/

On-Site Water Infiltration

Portland requires new construction projects to address stormwater infiltration on site. There are two paths to meet this requirement, depending on the area of the impermeable surface in your project (think roof size). For projects over 1000sf we place a dry-well on the site that captures stormwater runoff from the roof and allows it to infiltrate into the ground. Drywells have to be located 10' from building foundations and 5' from the property setback. Usually this isn't a huge challenge although sometimes it can be difficult to find a suitable location depending on the placement of the ADU in relationship to the main house on the site. If the roof size is smaller than 1000sf we can simply have drains or rain chains that lead to a splash pad, allowing rain to directly absorb into the ground.

Water Supply Size

There is a rather complicated equation that the city has to calculate the size of the water supply for a property. It counts all the fixtures, appliances and other water features on a property, each with a multiplier, adds them all up and this gives the size of the water supply. When adding an ADU onto a property you have to redo these calculations, adding in the toilets, sinks, laundry, showers, etc. from the ADU into the calculation. Often the updated calculations require a larger water services. This is a relatively large added cost to the permitting fees - around $2000 or more. There aren't many ways of getting around this without reducing the number of fixtures in an ADU. For instance, only one sink instead of two in the bathroom, no laundry machine, etc.


Separate Water Service Agreement

Along with water supply size, there is the issue of how the water makes its way to the ADU. Does the new dwelling split off the existing water lines running to the main house, or do you want a new water service directly from the street. The main reason to start a new water service from the street is that you can have the water bill for the ADU go directly to that address/tenant rather than being grouped into the water bill for the main house. This allows you to also pass on the cost of water to the tenants. However, there is also a large upfront cost to create the new water service. It is a tradeoff worth considering.

Most of our clients chose to just branch off of the main house water supply. This is because of the added upfront costs of installing the new service. In order to do this the city asks you to sign a Separate Water Service Agreement having the owner sign off on the fact that one bill is serving multiple units. Here is a sample of the agreement paperwork: https://www.portlandoregon.gov/water/article/221091