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Accessory Dwelling Units in Arlington: FAQs

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An ADU is a separate, smaller living unit with its own kitchen and bathroom facilities and separate entrance that is included within a larger resident (type 1), attached to a residence (type 2) or located in an accessory (“detached”) structure on the same lot as a main residence (type 3). For a variety of reasons, primarily cost and feasibility, the type 1 ADUs are by far the most common.

Article 43 on Arlington’s warrant for Spring 2021 Town Meeting would allow accessory dwelling units in connectin with single-family dwellings, two-family dwellings and duplex dwellings, as long as the ADUs can conform to dimentional requirements in existing zones (aka R0, R1, R2, B) and all code requirements. These dimensional requirements including setbacks, side yards, height, etc.

The sizes of these ADUs are determined by the size of the finished area of the specific home and must meet the dimensional requirements of the zoning district. Many homes in Arlington may not qualify for a Type 2 (attached) or Type 3 (detached) ADU. This chart shows the probable average square footage size of an ADU in each of the Town’s 21 precincts. There is a considerable difference, ranging from 479sf in precinct 4 to 885sf in precinct 8. The town wide average is 652 sf, not very big but a perfect size for an individual looking for a smaller, less expensive home in Arlington. No matter how big the home, the maximum size is capped at 900sf.

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Mothers Out Front Arlington Chapter Statement in Support of the MBTA Working Group Rezoning Plan

Mothers Out Front logo

Massachusetts is experiencing a housing affordability crisis and a climate crisis. For these reasons, Mothers Out Front Arlington supports changes in zoning by-laws that allow greater density in housing near public transit. Mothers Out Front is supportive of the  passage of a meaningful MBTA Communities Act that encourages the development of more multi-family housing and a greater diversity of home types in Arlington. A revised zoning by-law to allow for more multi-family housing will reduce pressure to build single family homes on undeveloped land elsewhere in Massachusetts. This safeguards undisturbed ecosystems and provides real alternatives to automotive commutes in the region, reducing both congestion and fossil fuel emissions. In addition, passing this by-law will allow Arlington to participate in the Massachusetts pilot for communities to build fossil fuel-free homes, thus ensuring that new construction in Arlington supports our net-zero climate goals.  

Mothers Out Front Arlington respects the public engagement activities that inform the Working Group’s MBTA Communities Act proposal. We appreciate that the Working Group is working with the Town to identify opportunities for developer incentives to encourage public open spaces, mitigate heat islands, and increase the tree canopy. Similarly, the Town’s commitment to maintaining current (and incentivizing higher) zoning requirements for affordable housing also is important to our group. For these reasons, Mothers Out Front Arlington strongly urges the Arlington Redevelopment Board to accept the MBTA Communities Act plan as proposed by the Working Group. 

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When was Arlington’s Housing Built?

The material in this post came from my efforts to learn about when Arlington’s housing was built. The data comes from the town’s 2019 property tax assessments, where I took our nineteen-thousand-and-some-odd homes and apartments and broke them down by housing type and decade built. It’s not exactly a history housing of production, though it is a close approximation. In this analysis, a single-family home built in the 1912 and rebuilt as a two-family in 1976 would show up as two units built in the 1970s. Similarly, a three-family home that was built in the 1924 and later converted to condominiums would show up as three condominiums built in the 1920s.

Here’s the visual summary:

Bar chart showing Arlington housing by decade built.

And here’s a small spreadsheet with the underlying numbers.

My first surprise was at how much we built in the 1920s: just under five thousand units. This was our biggest decade for housing production, and nearly double our second biggest (the 1950s). Another surprise was the 1990s; 132 of our homes were constructed during that decade, which is the smallest number since the 1870s.

What about homes constructed before 1850? There are only 117 of them, and they’re omitted from the data set. I’ve also omitted residential units in mixed-use buildings, since my copy of the assessors data doesn’t break mixed-use buildings into residential and non-residential units.

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Arlington Redevelopment Board Presentation on Articles 6-9

The presentation, dated March 11, 2019, includes slides used to present the information necessary to understand the rationale for zoning changes, the location of the zoning areas under consideration and the charts, tables and maps that help describe the situation. The proposed zoning changes, especially articles 6, 7, 8, 11 and 16, only cover changes affecting about 7% of the Town, those parts of the Town that are currently zoned R4-R7 and the B zoning districts.

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  2. Housing

Developers- A Dirty Word?

Last Spring, as Town Meeting considered zoning options for increasing the amount of housing, including affordable housing in Arlington, some citizens rallied against this effort. The reason: Housing is built by developers. Developers are greedy and can not be trusted. Ergo the community must prohibit developers. But much of the Arlington now cherished was planned and built by developers.

This article from the New York Times helps shed a perspective on the role of developers and suggests ways they are critically important to improving and revitalizing communities over time. Yes some developers’ interests may diverge from the community’s interests. Clear land use planning and regulations make it a better opportunity for both sides. Good developers bring skills in planning, finance, architecture and community engagement. They work with the risk that if they do the job well, they make some money. They could lose money. They don’t get paid by the hour. Both sides, community and developer, take risks. But there are rewards for each side too when the sides work together.

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State Reps Rogers and Garballey Support the MBTA Communities Plan

State Representatives Dave Rogers (Arlington, Belmont and Cambridge) and Sean Garballey (Arlington, Medford) have sent a letter to Town Meeting Members backing the MBTA Communities Plan. They write:

We believe the plan in front of Town Meeting provides a meaningful framework to address the housing shortage in Arlington.

To read the full letter, click here for PDF.

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  2. Fiscal Impact
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What Is Impact on Arlington School Costs of More Housing?

Does Arlington need more housing? If yes, will more housing result in higher school costs? There is a perception that more housing means more school age children and more school age children will strain the capacity and expand the budget of the Arlington Public Schools.

Prelimary reviews suggest that more housing would not strain the APS capacity for a variety of complex reasons. These reasons include: school age children do not always go to APS; by the time new housing came on line, the school enrollment, now growing, will have begun to decline; Arlington needs more diverse kinds of housing, not just family housing; the 283 units of housing that came on line through Brigham Square and 360 contributed more in property tax revenue than they cost in school enrollment costs…. by over $980K in 2019. Read this for more information.

More analysis is needed. More discussion is needed. These are complicated and nuanced issues. Readers with additional comments should send them to info@equitable-arlington.org.

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Arlington 2020: the Cost of Low-Density Housing

This is the second in a series of “Arlington 2020” articles. The first article looked at the number of one-, two-, and three-family homes and condominiums in Arlington, and how that housing stock has changed over time. This article will examine changes in the value of those properties. We’re going to look at “value” through the lens of property assessments, so we should start with an explanation of what property assessments are and how they’re used.

A property assessment is simply the Town Assessor’s best estimate of what a property is worth, based on market values. The assessor’s office inspects properties every ten years; during intervening years, assessments are adjusted based on sale prices of similar homes in a given tax neighborhood. For all practical purposes, assessed values tend to trail market values by two years. In my neighborhood, property assessments are spot on — my house was assessed at $501,000 in 2020; during 2018, sales of similar homes in the neighborhood ranged from $495,000 to $520,000.

Condominiums have a single assessed value, which includes land and buildings. Otherwise, assessed values are broken down into land value, building value, and yard items (e.g., a garage or a shed).

Assessed values are used to determine the tax rate. The assessors page on the town website has calculations in worksheet form, but for all practical purposes, it’s just a division problem. One takes the total tax levy and divides by the sum of all property assessments (in thousands of dollars), and that’s the tax rate. An individual’s taxes are the assessed value of their property (in thousands of dollars) multiplied by the tax rate. If an individual owns (say) 1% of the assessed value in town, that individual will pay 1% of the property tax levy.

The main point is that assessed values are based on market values, but with a two-year lag. Consequently, we can use them as a way to see how home prices have changed over time.

With that background information out of the way, we can look at some numbers. Here’s a graph of the median assessed values for condominiums, one-family, two-family, and three-family homes from 2013 through 2020. (the “median” is a value such that half of the assessments are above, and half are below).

Graph of Median assesed values by year and housing type
yearCondominiumSingle FamilyTwo-familyThree-family
2013$297,800$472,850$532,650$581,600
2014$300,150$484,400$530,000$574,800
2015$318,200$507,900$572,000$616,300
2016$351,050$546,300$623,150$673,550
2017$357,750$581,200$663,900$714,800
2018$395,400$618,800$732,100$787,600
2019$463,250$701,550$851,200$897,500
2020$473,100$771,900$944,000$1,010,850
%change58.87%63.24%77.23%73.81%

As one would expect, two-family homes are worth more than single-family, and three-family are worth more than two. Condominiums have a lot of variety; they could be half of a duplex, or a single unit in an apartment building. But a general upward trend is clearly evident.

These values are straight out of the assessor’s database, and not adjusted for inflation. The Bureau of Labor Statistic’s inflation calculator shows 12% inflation between 2013 and 2020; the %change is pretty considerable, even if one deducts 12% for inflation.

Next, I’d like to dig further into the 1–3 family assessments, by breaking them down into the value of land vs the value of buildings, and showing how that’s changed over time.

Single-family homes:

Graph of Land and building cost for single family homes, by year.
yearLand valueBuilding valueTotal assessed value
2013$243,700$226,300$472,850
2014$253,750$227,050$484,450
2015$272,700$229,900$507,900
2016$296,400$243,950$546,400
2017$326,400$246,400$581,250
2018$360,900$248,100$618,800
2019$440,400$250,400$701,600
2020$448,600$316,300$771,900
%change84.08%39.77%63.24%

Two-family homes:

Median land and building cost for two-family homes, by year
yearLand valueBuilding valueTotal assessed value
2013$202,500$320,550$532,650
2014$212,250$307,800$530,000
2015$256,400$309,800$572,000
2016$262,500$349,400$623,150
2017$307,000$350,700$663,900
2018$352,500$373,900$732,100
2019$478,300$374,850$851,700
2020$454,500$486,100$944,000
%change124.44%51.65%77.23%

Three-family homes:

Median land and building cost for three-family homes, by year
yearLand valueBuilding valueTotal assessed value
2013$200,100$377,900$581,600
2014$209,100$364,100$574,800
2015$249,800$366,550$616,300
2016$259,950$412,350$673,550
2017$298,100$412,500$714,800
2018$343,050$438,800$787,600
2019$459,000$440,100$897,500
2020$440,100$578,450$1,010,850
%change119.94%53.07%73.81%

There are several things worth pointing out in these breakdowns.

First, note that the land and building values “jump” a bit between 2019–2020. 2020 was one of our full reassessment years, so I’m willing to attribute this to a periodic course correction. The total increase is generally linear, but the land/building composition has changed.

Second, the median land value for single-family homes is higher than the median building value, for all years between 2013–2020.

Third, most of the increases come from changes in land value. I believe this comes down to location, location, and location. Arlington has a well-respected public school system, and it’s close to universities and tech centers is Cambridge and Boston, and office parks in Lexington, Waltham, and Burlington. City amenities are close at hand.

So what does one do about our rising home prices, and in particular, the rising value of land? The first (and perhaps default) answer is to do nothing. Rising property values are a boon to homeowners who purchased a capital asset (i.e., a house) in the past, and have seen its value appreciate over time. The downside of doing nothing is that each year, increasing housing prices create an ever-increasing income threshold for new residents.

An alternative approach would be to allow more (and smaller) units to be built on each lot. This requires reconstruction or redevelopment, but it allows the cost of land to be amortized among several households. More units/lot means more people and more density, but it reduces the income threshold for buying in to Arlington. (Note that the per-unit cost for three-family homes is lower than the per-unit cost for two-family homes. Similarly, the per-unit cost for two-family homes is lower than the cost of a single-family home).

A third article will look at the distribution of housing prices in Arlington, and how the distribution varies by housing type.

Here is a spreadsheet of data shown in this post.

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