Summing up ADU research: are accessory dwelling units as great, or as horrible, as people say?

I am by nature a skeptical person, who rather enjoys debunking things. So, a few years ago, when I decided to dig into the many hopes and fears about accessory dwelling units (also known as ADUs, granny flats, in-law units, laneway houses, etc) I knew I might end up shooting myself in the foot. After all (full disclosure here), I have an ADU of my own, and am one of the editors of a site about ADUs. I had a notion that this form of development was a promising nod towards a gentler, more sustainable society. But what if it turned out there was no objective evidence that ADUs had any benefits beyond my own yard?

I carried on because the civic “discourse” about ADUs drove me nuts. It had an endless, cyclical quality, like those discussions sports or comic book guys can get in to: who was better, Babe Ruth or Willy Mays? Could Batman beat Superman in a fight? Could Superman beat Captain Nemo? When there is no real evidence to be had, you can stay at the bar all night. 🙂

photos by Steve Lewis of the Durango Herald (left) and Laure Joliet of the New York Times (right)

In the noisy confines of local planning meetings and “Letters to the Editor” pages, exchanges went like this:

• ADU advocates said ADUs would create affordable housing, house older citizens (less popularly known as “the elderly”), create “green,” less car-dependent housing, and generally strengthen informal family and neighborhood ties.
• ADU opponents said that ADUs would create parking problems, bring down property values (and generally bring in undesirable people), create overcrowding, change the appearance of neighborhoods, generate noise and garbage, and perhaps end the single-family nature of existing neighborhoods.

Meanwhile, in the more formal literature, there were some comparative analyses of policy.

In short, there was plenty of talk about the idea of ADUs, but virtually nothing about the reality of them. There was close to zero factual information about how many ADUs exist, who lives in them, where they are, how many cars come with them, and so on – the kind of basic factual information that should inform policy and debate.

I set out to collect and discover those basic facts. Fortunately in the last few years some objective data has been published about ADUs (listed in my post about research needs), and in this series of posts, I’ve expanded those findings as much as I dare. To sum up, here’s what this series has uncovered:

In short, there is compelling, if early, evidence that ADUs benefit the community in the areas of environmental impact, reduction in car use, and a non-institutionalized style of affordable housing. I also anticipate that positive effects for older citizens (“the elderly”) will become more notable as time goes on.

Meanwhile, I have found zero objective evidence supporting two specific fears often mentioned by ADU opponents: parking problems and declines in property values. This is not to deny those things could ever happen – perhaps new evidence will emerge – but there is no basis for them right now.

When it comes to the less objective hopes and fears mentioned by ADU advocates and opponents, such as (paraphrasing here) ‘strengthening family ties’ or ‘bringing in undesirable residents’, it is harder to measure things and make statistical comparisons. However, the anecdotal accounts in comments from ADU owners, and in the case studies on accessorydwellings.org, are so consistent I feel confident making a few more tentative conclusions.

ADUs support families in several ways. They serve as a flexible resource that provides stabilizing income during some phases of life and provides housing for extended family during other phases. When they are housing family members, their simultaneous proximity and independence allows naturally supportive relationships to work smoothly. For example, when grandma lives in the ADU, she gets the help she needs with stuff like shopping, and can trade back child care – no commuting, appointments, or day care centers necessary.

These kind of informal support services seem completely natural to the people who experience them.  They’d probably be amazed to learn that, in some cities, Grandma wouldn’t legally be allowed to live with them — at least not if she had her own apartment downstairs.  When you express single-family zoning in this way it sounds extreme, yet that zoning applies to much of our population.

ADUs show there are many ways that families can live together.  In this way, they are quiet refutation of the Leave It To Beaver “nuclear family” ideal, where a “normal, healthy family” is two parents and their children, and other relations and friends are distant satellites. As far as I can tell, very few people, even arch-conservatives, believe in this radical version of familialism anymore, yet zoning tries its best to enforce it.

Second, ADUs are a small but meaningful step toward sustainable housing. What sustainability really means is a pretty big discussion that won’t fit in this blog post. However, it seems safe to say that sustainability involves finding a better balance between the production and consumption of essential resources (e.g. energy supplies). And that, I’d venture, involves making a choice of quality over quantity in lifestyle. As the case studies on accessorydwellings.org show, ADUs can provide a pretty high quality of life in small spaces that are inherently greener than the standard “SFR”. That quality of life comes not necessarily from the building itself but its context– e.g. to family, transit, etc.

ADU critics must be acknowledged at least one way. It is true that ADUs are “infill” development that densifies existing neighborhoods. Yes, they are a mild, incremental form of densification in the sense that each individual ADU is only a tiny change that can have little effect on neighborhood conditions. But over decades an accumulation of ADUs probably would notably change the character and demographics of a place.

But, can any neighborhood really be held in an unchanging state?  The implied message of some ADU critics is that banning ADUs will prevent or slow densification or at least remove it to some distant place, where it will be more acceptable. But these are not reliable assumptions. If there are economic forces driving densification or gentrification, they will be expressed somehow – for example in rising prices and unpermitted ADUs. The question for many communities is not “should we have ADUs or nothing?” but rather “are permitted ADUs a good choice compared to the other options out there – such as transit-oriented developments, townhouses, gated single-family developments, or a new crop of unpermitted ADUs?”

Portland’s experience in the last few years provides an interesting comparison. Hundreds of permitted ADUs have been created, and there has been practically no reaction on a neighborhood basis — sometimes the new developments are hardly noticed. Meanwhile, an alternative form of densification, the transit-oriented apartment block, has caused a lot of protest.

ADUs are not a panacea. They cannot solve every urban, family, or environmental problem. But, as I’ve documented in this series, they clearly have some benefits in those areas compared to standard American mode of “single family” development. Those benefits need to be quantified more, especially with comparison to other densifying forms of developments, but I have little doubt they exist.

Beyond that, ADUs are simply a refreshing grassroots alternative to “big” development. To a design buff like me, there’s something tiresome about big apartment blocks, rowhouses, and other “professional” developments, no matter how well thought out. You can practically see the investment calculations floating over them, like the furniture prices in Fight Club.

This post’s single-serving friend.

In contrast, ADUs are typically created and managed by homeowners, not real estate professionals. These homegrown residences are unique, each with a purpose and a story.  Though the biggest single motivation for creating ADUs is financial gain, a notable fraction of these “amateur” developers make a fascinating choice – to not maximize investment return, for a month, a year, or a decade, so they can house a family member or a friend, start a business, or do something else to spread good beyond their yard. In short, they often show that people value things beyond money, and that may be the best pro-ADU argument of all.

About Martin John Brown

Martin John Brown is a researcher and consultant on environment and housing. Find out more at http://martinjohnbrown.net.

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