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Accessory Dwelling Units

Updated: Sep 14, 2020

Many of you have been wrestling with integrating the recently passed State legislation (AB 2299 and SB 1069) that requires most cities to accommodate second dwelling units, referred to as “accessory dwelling units,” within your development rules and regulations.

Regardless of your own city ordinances on the issue, the new state law is probably more permissive, and so you will probably need to get busy amending your local ordinance to comply with the new broader state law.  I will not bother to get into the arguments for or against such dwelling units, as the die appears to be cast.

Accessory dwelling units are limited to parcels that have a “single-family home,” and yes, we all see the irony in the use of “single family home”.  The amended law allows accessory units up to 1,200 square feet.  You may continue to establish standards governing height, setback, lot coverage, landscaping and architectural review, with a few minor exceptions.  Not surprisingly, the new law is not without confusion in that your city may exclude accessory units in certain areas if you can make supportable findings that the delivery of water and sewer services, adequate traffic flow and the public safety responses of police and fire/medics may be compromised.  Which leads me to my interest in the issue. Given that each accessory unit will increase demand upon existing city infrastructure and thus service levels, can the city impose development impact fees (henceforth referred to as DIFs) on these private facilities as part of the approval process? My answer is no, yes, or at least probably.

Two Types of Accessory Units. There are two types of accessory dwelling units identified in the legislation.  The first is one created from space within the existing main dwelling unit such as a large bedroom, attic or basement that can be turned into a small living unit.  We will refer to those as “Existing Space Accessory Units.” The second would be a new unit up to a maximum of 1,200 square feet that is either attached or detached but increases square footage outside of or on the top of existing structures.  We will refer to these as “Additional Space Accessory Units.”

Application of Accessory Units DIFs Derived From Existing Space. Sorry, but this is not likely to happen.  These units that derived from existing space are specifically protected from DIFs, at least the higher water and sewer DIF’s.  You may be able to apply other DIF’s such as public service, circulation and such, but adequate demand nexus will be difficult to find.  Also, if the accessory unit space is made from an existing room, there probably isn’t a great deal of impact anyway.  Most of you have a per unit DIF schedule, that is, the impact fee does not vary depending upon how many bedrooms there are in the detached dwelling.  I’d leave that alone because it is never good government policy to push people into a position where being less than forthright is a viable option (“Honestly, it’s a den”).

Application of Accessory Units DIFs Derived From Additional Space: This type of new unit will have the greatest identifiable additional service demand impact on the City’s infrastructure and there do not appear to be limitations to imposing DIFs, beyond the normal Government Code Section 66000 nexus requirements.

Law enforcement and fire/medic impacts, though likely, will be difficult to identify simply because there is not sufficient demand data.  This type of housing is not identified in the National Fire Incident Reporting System (NFIRS) incident reporting list, nor would any police department keep such records.  There is not an accessory dwelling unit category within the Institute of Transportation Engineers (ITE) trip-end generation data due to the difficulty in extracting the new demand from this precise use from the demand generated by the main full-sized housing units.  Census data does not identify this type of dwelling unit nor the number of people within them, so we are at a loss of determining a statistical average dwelling density for such units forcing us to speculate and/or guestimate.  Without this data it will be difficult to calculate the impact of such new dwellings on the Quality of Life infrastructures (libraries, community centers and parks) for which service standards are per-person based.   If the new second unit ties into the existing water and sewer lines it will also be difficult to immediately ascertain those demands.

I do not have the answers yet, but I am working on some ideas.  When I flush out some workable models I will post it in one of our monthly newsletters.

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