Question

I live in Washington state and own a house in a residential area. I would like to build a tiny house in my backyard to rent to local college students. My plan is to build it on a foundation. Is this legal in the state of Washington?

Answer

In Washington state, zoning regulations vary between jurisdictions, so the answer to your question may depend on where you live. To determine whether a tiny house is lawful on your lot, you will have to carefully review local zoning regulations. This article will provide you some background information to help jumpstart that research.

Zoning Regulations Control the Use of Land in Washington State

In Washington, local governments usually codify zoning controls in a development code or land use code. The land use code will be part of the jurisdiction's general code. For example, the city of Vancouver, Washington’s development code is in Chapter 20 of the Vancouver Municipal Code. You'll find Spokane County’s zoning code inChapter 14 of the Spokane County Code.

If you do not already know for sure, it is important to find out exactly how your property is zoned. For example, your property might be in a “single-family residential” or “light industrial” zone. To find out, you can call the local planning department.

Some governments have interactive websites that allow you to research your property by inputting your address. For instance, if your property is in King County, you can go to the County Assessor’s website and run a report with just your address.

The next step is to see what uses are allowed on your property based on the zoning. In a case like yours, where you plan to use the tiny house as an accessory dwelling, you will want to review the code provisions that relate to your zone (and any applicable overlay district) to see whether accessory dwelling units (or similar uses) are permitted. Sometimes detached ADUs, like a tiny house, are referred to as "backyard cottages."

You will not necessarily review the code for references to "tiny houses." Instead, you will want to focus on whether the intended use, in this case as an accessory residential dwelling, is lawful. If, for example, you planned to use it as a home office or art studio (not an ADU), the answer to whether it is lawful may differ--even though it's basically the same tiny house, identical in appearance and location.

Your Local Zoning Code's Development Standards May Prohibit Tiny Houses

Zoning codes in Washington also include development standards that guide development in each zone. Development standards include requirements relating to setbacks, lot coverage, height restrictions, utilities, parking, landscaping, and even lighting.

Some of these standards can make development of a tiny house difficult. If, for instance, your backyard is small, you may not be able to comply with setback requirements or be able to develop the required parking space.

It is also possible that your jurisdiction imposes a minimum dwelling size, for example, 600 square feet. If such a requirement exists, you will need to make sure your tiny house will be big enough.

On a related note, you should also review any private land use restrictions. As an example, Covenants, Conditions, and Restrictions (CC&Rs) control the development of property in subdivisions or communities governed by homeowners' association (HOAs). In fact, subdivisions sometimes have stricter development standards than local governments. If applicable, it is important to review any CC&Rs and other development restrictions carefully to see whether tiny houses are allowed.

Washington Building Codes Include Safety and Construction Standards

For site-built tiny houses built on a foundation and intended for human habitation, the applicable building code will dictate what you can and cannot create on your property. Building codes include construction and safety standards relating to the foundation, electrical components, insulation, egress (ways to exit the dwelling), protection from moisture, and plumbing.

In Washington, local governments adopt the International Building Code (IBC) and make any appropriate amendments. For example, the Seattle Building Code (SBC) is the IBC with adopted amendments specific to Seattle’s needs.

One common hurdle for tiny-house builders trying to follow the IBC is the minimum habitable room size. Under the IBC, every dwelling must have at least one habitable room that is 120 square feet. (SBC Sec. R304.) In the case of a tiny house, you must take this requirement (amongst others in the building code) into account during the design phase.

Ask an Attorney for Help in Understanding Complex Regulations

Land use regulations can be difficult to understand if you are new to reading them. Talking to a Washington land use attorney about your case will ensure that you receive advice based on the applicable zoning ordinance for your property. Failure to comply with all applicable laws could lead to a code enforcement action and a fine, so following the rules is important.