A Portland-Brand Building Boom: Accessory Dwelling Units

It's possible that construction permits for accessory dwelling units, also known as granny flats or mother-in-law units, could surpass permits for regular homes.

1 minute read

March 3, 2017, 2:00 PM PST

By James Brasuell @CasualBrasuell


Accessory Dwelling Unit

radcliffe dacanay / Flickr

"Portland's new housing stock is getting miniaturized, with builders planning nearly as many accessory dwelling units as regular single-family houses," reports Steve Law.

Law is sharing data from the city's Bureau of Planning and Sustainability and Bureau of Development Services, which shows "the city issued 615 building permits for new accessory dwelling units or ADUs in 2016, approaching the 867 permits issued for regular houses."

The news is partly enabled by the tough conditions for single-family housing construction in the city. "One reason single-family construction seems to have plateaued is the lack of undeveloped large parcels of land, forcing homebuilders to focus on infill homes on vacant lots or replacing demolished homes, rather than traditional subdivisions," explains Law.

Still, the city of Portland's ADU laws are considered lenient, and the cost of constructing an ADU at the maximum size of 800 square feet is about $160,000. Planetizen last checked in with the effects of Portland's ADU regulations in 2014, after a study found that the units create relatively low impacts from increased automobile traffic. Since then, however, more cities are following Portland's example.

Thursday, March 2, 2017 in Portland Tribune

portrait of professional woman

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching. Mary G., Urban Planner

I love the variety of courses, many practical, and all richly illustrated. They have inspired many ideas that I've applied in practice, and in my own teaching.

Mary G., Urban Planner

Get top-rated, practical training

Logo for Planetizen Federal Action Tracker with black and white image of U.S. Capitol with water ripple overlay.

Planetizen Federal Action Tracker

A weekly monitor of how Trump’s orders and actions are impacting planners and planning in America.

April 30, 2025 - Diana Ionescu

Close-up on Canadian flag with Canada Parliament building blurred in background.

Canada vs. Kamala: Whose Liberal Housing Platform Comes Out on Top?

As Canada votes for a new Prime Minister, what can America learn from the leading liberal candidate of its neighbor to the north?

April 28, 2025 - Benjamin Schneider

Hot air balloons rise over Downtown Boise with the State Capitol building visible amidst the high rises.

The Five Most-Changed American Cities

A ranking of population change, home values, and jobs highlights the nation’s most dynamic and most stagnant regions.

April 23, 2025 - GoodMigrations

People biking along beach path with moored ship in San Diego, California.

San Diego Adopts First Mobility Master Plan

The plan provides a comprehensive framework for making San Diego’s transportation network more multimodal, accessible, and sustainable.

2 hours ago - SD News

Sleeping in Public

Housing, Supportive Service Providers Brace for Federal Cuts

Organizations that provide housing assistance are tightening their purse strings and making plans for maintaining operations if federal funding dries up.

3 hours ago - KSL

Conductor walks down platform next to Amtrak train at station in San Jose, California.

Op-Ed: Why an Effective Passenger Rail Network Needs Government Involvement

An outdated rail network that privileges freight won’t be fixed by privatizing Amtrak.

4 hours ago - Streetsblog USA

Urban Design for Planners 1: Software Tools

This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.

Planning for Universal Design

Learn the tools for implementing Universal Design in planning regulations.

Building Inspector

Village of Glen Ellyn

Manager of Model Development

Central Transportation Planning Staff/Boston Region MPO

Senior Planner

Heyer Gruel & Associates PA