Successful Appeal of the County's Initial Assessment of the Contributory Value of the ADU

In my last post, I described how the county attributed approximately $142K of contributory value from the new ADU. This translated to a HUGE annual property tax hike; from $1,599 to $4,021.

What I didn't describe in that post was that upon receiving the County letter in the mail, I immediately gathered together evidence that my ADU was actually worth far less (it is worth ~$100K) and wrote an appeal to the County Board of Property Tax Appeals. I submitted the appeal package in full the following day at the County tax office.

When I spoke with the kind lady behind the County desk, she informed me that the assessor, who I'd allowed into the property, had noted in his records that I had added a 1,350 sq ft ADU. Given that the City of Portland's regulations only allow ADUs of up to 800 sq ft, I had evidence to prove that his spatial calculations were necessarily off target by ~68%. I also learned that the County assessor likely applied a simple numeric formula to this miscalculated sq footage to come up with the obscenely high contributory value for the ADU of $142K (eg. 1,350 sq ft x $105 sq ft= $142K).

A couple months after submitting my appeal paperwork, a 2nd assessor contacted me and visited the property. When he arrived, he explained that he had read through my appeal documentation, which had included a full copy of a 3rd party appraisal. Upon visiting and measuring the property, he concurred that the initial assessment of the size of the ADU seemed incorrect and he shared that he'd never seen an ADU add more than $100K to the value of a property.

It's worth noting that the initial County assessment apparently included the ADU attic space in his sq footage calculations, whereas the City did not count the attic as living space. The 2nd assessor agreed that the attic should not be counted in the sq footage calculations.

It's also worth noting that the County assessment includes the total building footprint (i.e. the exterior walls) in the sq footage calculation, whereas the City only counts interior space (i.e. drywall to drywall). The County includes exterior dimensions because assessors must be able to assess the building from the outside since homeowners aren't required to allow assessors entry into the home and many homeowners deny entry. These two variables help explain why the first sq ft assessment was so off target. However, I never would have known about this sq footage miscalculation had the kind lady behind the desk not mentioned it; this 1,350 sq ft figure wasn't in the initial letter they sent.

Today, I received an updated property tax assessment in the mail, which I am happy to report, accurately attributes ~$90K of contributory value from the ADU to the property, $53K less than their initial assessment!

The "From" column relates the 2013 figures from the "This Year" column in the first image at the top of this post.

The "To" column shows the new figures according the 2nd assessment, which will override the initial assessment.

Whereas the initial assessment indicates the market values of the structures (main home and ADU) at $320,600, the new assessment has the market values of the structures at $267,600. The new assessment values the ADU at ~$90K, which tracks perfectly with my cost of construction and my private appraisal.

I don't yet have a newly updated tax bill, so I don't know what my actual annual taxes will be. But, I estimate that the updated tax on the property will probably come be about $3,100/year. Once I receive the final property tax bill, I'll post it for all to see.

If my estimate is correct, this will be $1K less per year than the initial County tax assessment. It is still a $1,500/year increase to the property tax, a two-fold increase from what my taxes had been before I built the ADU. But, based on the County tax regulations, this new property tax burden seems fair and reasonable.

Common Forms of Living Smaller

Much residential "green building" attention has been placed on material selection, alternative power sources, and mechanical efficiencies. These choices all play a role in building "green", but arguably, none of these charismatic green features are as important as the energy efficiency gains achieved through building and living in smaller spaces. 

Smaller houses can take many forms, and the three common forms that I'll mention in this post, all achieve notable reductions in terms of their environmental lifecycle impact reductions: Multi-family, ADU, and "Tiny Houses" 

Let's begin with the recent EPA-sponsored report about the energy impacts of residential housing choices. As stated on the introductory page, 

"Buildings and transportation together account for about 70 percent of energy use in the United States and are responsible for about 62 percent of U.S. greenhouse gas emissions"

The findings in this report illustrate that certifiably green buildings are not as significant in reducing that energy as where you build (Conventional Suburban Development or Transit Oriented Development) and the housing type (Single Family Detached, Single Family Attached, and Multi-Family). The report findings are summarized well in this rich graphic.

For me, I’m beholden to my innate desire to design and build something on my own terms. There are strong correlations between the size of average Single Family Detached, Single Family Attached, and Multi-Family homes. However, the impact of housing size perhaps has a more direct correlation to energy use than those building type descriptions.


From 1950, to 2008, the average sq ft per person has increased from 259 ft to 961 ft, a 372% increase. 

ADU’s are an accessible way for urban homeowners to make a big stand on issues that span community building, environmentalism, urbanism, and climate change. Done well, ADU’s present a compelling personal financial opportunity for individuals to create a regenerative, personal financial portfolio. I plan to discuss the economics of my ADU and ADUs at large in future posts. 



I have extracted some graphics from a presentation about the findings from the Oregon DEQ report, "Life Cycle Approach to Prioritizing Methods of Preventing Waste from the Residential Construction Sector in the State of Oregon". I anticipate this this groundbreaking report will prove to be pivotal in the green building movement and will help to instigate a shift toward an emphasis on living smaller. 

I believe ADU’s will naturally become more and more popular where there is sufficient housing demand and where they are allowed by zoning laws. With a few exceptions in the US, ADU’s are not legal.

The first ten minutes of this video is of Jay Shafer of Tumbleweed Tiny Houses addressing code barriers to small housing. Jay Shafer is the person who has popularized the notion of building tiny houses on wheels- which, as he explains, is simply a tactical exploitation of a common municipal zoning loophole to legitimize what would otherwise be illegally constructed tiny houses.