Accessory Dwelling Units Add to Housing Supply, Reduce Cost

Accessory dwelling units are separate housing units that lie within a single-family home, or a separate detached structure on the same lot with a larger home. Examples are carriage houses in historic neighborhoods, alley houses, mother-in-law quarters, a small rental unit within what was originally a single-family home, or above-the-garage apartments in either attached or detached garages.

Once in disfavor, accessory dwelling units, sometimes written as ADU's, now are touted as a solution to affordable housing, particularly in expensive housing markets. They also may resolve the need for extra income for an older homeowner who no longer needs so so much space. Another advantage may be that adult children, older parents, or in-laws or other relatives are able to stay in familiar quarters that are familiar to them.

In late 2009, Seattle approved an ordinance allowing backyard cottages in single family zoning districts throughout the city.

Foreclosure, Recession, and Accessory Dwelling Units

Although the movement to support the concept of modifying zoning regulations to allow accessory units in single-family districts has been gaining momentum since at least the late 1980s, the current economic crisis makes this idea seem even more sensible.

Real estate taxes in many areas of the country are quite burdensome to elderly homeowners, and sometimes to those who are slightly too young to qualify for state exemptions for seniors. Allowing an accessory unit brings in income that can be used to maintain the main dwelling and pay taxes and insurance.

Permitting accessory units may be helpful in the foreclosure crisis in a couple of respects. Large recently constructed homes that are no longer affordable under stricter lending standards might not lie vacant for years in overbuilt markets if accessory dwelling units are permitted. This would allow prospective homeowners to cover part of their mortgage through renting the extra unit.

In many cases, a second story, portion of the garage, basement, or great room with a wet bar could form the nucleus of a small apartment. In other places, giant backyards are quite conducive to constructing a small house in the rear of the main house, even with a somewhat private yard area.

In Support of Historic Preservation

Relaxing zoning regulations to allow accessory dwelling units under specified conditions and in well-considered geographic boundaries can also enhance the likelihood of restoration of historic homes. These projects are financially and logistically daunting, and a municipality can help make them more feasible if there is a prospect of an income stream to help support acquisition of the property.

In some older neighborhoods, alleys, alley garages, and old carriage houses are quite helpful in devising unobtrusive ways to add an accessory dwelling unit without inconveniencing the homeowner in significant ways for months at a time. These arrangements also permit the tenant a greater measure of privacy as they enter and leave their abode.

Other Benefits of Loosening Zoning Regulations

Accommodating population growth and formation of new but small households through alley or carriage houses also has the advantage of supporting programs that discourage sprawl and promote compact development patterns. Where there are alleys, the addition of a small home in the rear of large yards is an especially easy proposition.

Accessory dwelling units benefit a municipality by keeping down the cost of extending utilities while still increasing population. Since household size has been declining steadily in the U.S., population growth within the existing footprint of the town will be very welcome in some situations.

Yet a third advantage is the additional safety that seniors may feel with someone else on the premises. Even a caregiver unit might results from a more lenient set of regulations.

What Are the Barriers to More Accessory Dwelling Units?

Since this practice offers such an array of advantages, you might rightfully ask why it is not more widespread. The answer probably lies in tradition, inertia, and general resistance to change. Many folks fiercely defend a strict one-family, one-lot policy, which is well entrenched in zoning in the last 80 years.

However, the good news is that when the reasons are compelling enough, we really can change. This treatment is especially appropriate where both a large older population and a large younger population are willing and able to co-mingle. Another winning recipe is a somewhat affluent (or once affluent) crowd in the same space where a number of service workers or college students need to be.

Let's install some safeguards, permit accessory housing through the zoning ordinance, and then launch a campaign to explain the advantages and build awareness among construction professionals of the potential in this market.

If you want to limit the right to add these units, here are some possible provisions to add to the zoning ordinance:

1. Limit the number to one accessory dwelling per main dwelling lot.

2. Require site plan review and approval by the planning commission and/or city council if any new structures are built.

3. Require the building commissioner to review the actual capacity of each of the proposed accessory dwelling units to provide the basic activities of living: living, sleeping, eating, preparing food, and sanitation.

4. Allow the accessory dwelling units only on lots of a certain minimum square footage.

5. Limit the occupancy of the accessory unit, based on its square footage. While this is covered in the zoning ordinance or another code already, in all likelihood, you may want to review this in light of particular examples that you might concoct.

6. Specify a maximum percentage of the existing building that can be altered.

7. Allow only relatives to occupy the accessory units.

8. Regulate whether the property owner must continue to live in the main unit.

9. Limit the ability to provide accessory dwelling units to homes of a certain vintage.

10. Require a separate lawn and/or separate garage or driveway for the accessory unit. Or conversely, if more suitable for your neighborhoods, don’t allow a separate driveway or garage.

11. If you have any municipal capacity for architectural review, definitely add this layer to the ordinary review process.

12. If you like the idea but don’t want too many accessory units, specify by law the maximum number of units on a block, within a district, or within a radius of another accessory unit.

13. Lastly, definitely preserve the notion of a main unit and an accessory unit. One should be appreciably larger than the other to assure medium-term viability for the units.

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