Accessory Dwelling Units (ADUs) are separate housing units built on existing single family residential properties. ADUs are also known as second dwelling units, guest houses, backyard cottages, mother-in-law units and granny flats. 

There are many different types of ADUs, including both separate structures located in a back or side yard (detached) and conversions of existing spaces such as basements, attics and garages (attached).


If you would like to learn more about ADUs, the website accessorydwellings.org is a valuable resource.

Why are adus becoming more popular?

Thousands of new ADUs are being built in communities across the U.S. because they are a manageable and minimally-disruptive option for adding desperately needed housing to existing neighborhoods. Moreover, ADUs typically cost less than other forms of housing and make efficient use of existing land.

The other factor driving ADU adoption is that they serve so many varying needs that mirror socioeconomic trends in the U.S. ADUs allow for people to age in place or form multigenerational households to ease caregiving responsibilities and cost. Homeowners, given the high cost to buy a house, are frequently turning to ADUs to provide additional income to make ends meet. Lastly, the appeal of downsizing and minimalist living seems to be growing and ADUs allow people to simplify their lives and still live in a neighborhood setting.


Zoning, regulations and fees vary by municipality but most city zoning codes allow for ADUs. In addition, most municipalities view ADUs as critical to providing affordable housing in rapidly growing neighborhoods and have modified local codes to allow for ADUs.

The largest cities on the West Coast, including Portland and Seattle, all allow ADUs and continue to update codes and fees to encourage the development of ADUs. In addition, the States of California and Oregon have passed state laws which preempt local prohibitions on ADUs.


A Dweller ADU is a self-contained living space with the look and feel of a house brought down to small scale. Each Dweller ADU is approximately 450 sq ft. and has a living space, a kitchen with full size appliances, a bathroom and a bedroom. High quality materials with full sized windows and doors are used during the construction of each unit. For the exterior, landscaping to provide privacy between the primary unit and the Dweller ADU is employed.

WHAT IS THE COST of a dweller adu to a homeOWNER?

Dweller sells fully installed ADUs in the Portland metro area for a fixed price of $130,000. This price includes all permits, installation costs, utility connections, appliances, and landscaping. A Dweller ADU is one of the most affordable options for a detached ADU.

Because of the variability of site characteristics, Dweller’s fixed price will not cover the cost of removing existing structures, large trees, underground storage tanks and cesspools, and other impediments to installing an ADU, nor will Dweller cover the cost of non-standard installations or utility connections, or upgrading utility service to a property to serve the ADU (see below). In addition, because the SDC or impact fees charged by many local governments vary widely, these costs are passed through to the property owner.


Typically, homeowners must hire an architect and a contractor, and take care of permits and other paperwork. Some homeowners choose to perform one or more of these tasks themselves. Dweller is responsible for all of these tasks, including design, permitting, construction and installation of the ADU. As part of this model, Dweller’s fixed cost covers not only the cost of construction and installation, but also the cost of permitting, utility connections and landscaping.


Many different types of properties will accommodate an ADU. In most cases, properties with a flat backyard with few obstructions, and where an open space with minimum dimensions of 45’ x 25’ can be created, will work. If you aren’t sure, contact us and we’ll review property information online and even perform a site visit to determine if your property is suitable for a Dweller ADU.


The monthly rents for an ADU typically reflect neighborhood market rents. For example, in Portland, Oregon, rents for a single family ADU are roughly $1,000 to $1,500 per month.

how do adus affect the sale of my house?

The presence of an ADU can often enhance the attractiveness of a house on the market, and increasingly investments in new ADUs are being reflected in the appraised value of those properties.

Do ADUS increase my property taxes?

The installation of any ADU will result in an increase in property taxes equal to the assessment of the ADU as an improvement to the property. The addition of an ADU should not result in a new assessment of the rest of the property. The homeowner’s property tax bill can still increase as a result of standard annual increase in taxes and new levies that are added to property taxes each year unrelated to the ADU.

How does a Dweller ADU access sewer, water, electric and gas service?

Dweller ADUs access sanitary sewer and water service by connecting to the main sewer and water service to the primary residence. In most cases, a connection to the sewer is established outside the primary residence, and a connection to water service is accessed through the foundation into the basement of the primary residence. Dweller ADUs connect to existing electrical service through either the main panel or a separate panel on the outside of the house. Dweller ADUs do not use natural gas so a connection is unnecessary.

What if existing water, sewer or electric service is insufficient to support an ADU?

The existing service to typical single family residences is usually sufficient to support a Dweller ADU. In the event that it isn’t, Dweller will work with the property owner to upgrade the necessary service to support the ADU. The cost of upgrading water or sewer service or establishing upgraded electrical service is not included in Dweller’s standard model and would be borne by the homeowner. 

What about cable, phone service, garbage and recycling?

Dweller will establish separate cable and, if desired, phone service to the ADU. If the ADU is rented out, these bills can be assumed by the tenant.

In most cases, the homeowner will add another garbage receptacle to their monthly bill and bill the tenant for the additional cost. Existing recycling receptacles should be sufficient for the ADU’s recycling needs.

What about mail service?

 All permitted ADUs are assigned a separate mailing address usually by adding A to the primary residence and B to the ADU. When requested, Dweller will install a separate mailbox in a location compatible with existing mail service.