ADUs in Clark Coiunty
ADUs in Clark County Since we specialize in multigen homes, we often receive requests for information about Auxiliary Dwelling Units (ADUs) in Clark County, WA. ADUs are a desirable alternative for multigen living, provided you know the guidelines in your local area. Recently a rural homeowner on 5 acres asked about the ADU regulations in her area. So, let’s review the current status of ADUs in Clark County.

ADUs Are Legal, But…

The basic rule is, ADUs are legal in both urban and rural areas. But the allowable buildings are different. If you are in city limits, you are allowed – within certain guidelines – to add a separate structure up to 800 SQFT. It could ]be larger if incorporated into an existing structure.* In rural properties, separate ADU structures are simply not allowed.

Rules for Rural ADUs

For purposes of this article, we will concentrate on rural properties. County guidelines say any residential home on at least one acre can add an ADU. But it must be within or attached to an existing residential structure. This usually means upgrading a basement, attached garage, or adding to the current structure. Again, as long as it is attached. There is just no provision for adding a separate ADU structure, no matter how large the property.

Multigen Families Like ADUs

Most multigen families want privacy and separate living areas so they’re not stumbling over each other. The ideal solution for that is to convert an existing daylight basement with separate entrance, as we did with our home. The other alternative is to expand the existing house with an attached structure – often, a simple breezeway or deck will be sufficient to pass code. These are issues you should review with your local permit department. Having said that, we have seen homeowners who had built separate structures called “studios” or “offices”.  They have a bedroom, bathroom, and kitchenette sink with counters. This is allowed, and will be permitted, but it cannot have a stove. So, many homeowners will build the studio, get the permits, then after the inspection install a stove.  We are not condoning this, of course, but county officials acknowledge this is a common practice in rural areas.

First Things First

If you are considering a rural ADU, the first issue is whether the existing septic system and well can support an additional bedroom or two. The state’s chart shows accepted guidelines for septic sizing:
You will need to check with your local Health Department to see if your current system will support an ADU. Their analysis will include not just the tank size, but also the capacity of the drain field. If neither is sufficient, you will need to expand the current system, or install a separate system. Some homeowners decide to “decommission” a bedroom, and assign it to the new ADU. This is tricky because, though legal, could present problems at resale or for appraisers down the road. Also, if you decide to build a “studio” without a stove, you will not be able to consider it an ADU for resale purposes. If you have any questions about ADUs and guidelines for building, feel free to give us a call. * Be aware that The City of Camas has a restriction that the main house needs to remain owner-occupied at least 6 months out of the year and at no time may the owner charge rent for the main living area. Plus, you may have to install a fire sprinkler system.
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