Expanding ADU Development and Occupancy: Solutions for Removing Local Barriers to ADU Construction

By David Morley, AICP, Shannon Guzman



Accessory dwelling units (ADUs) are a valuable tool to help communities broaden housing choice in single-family neighborhoods. In recent decades, many communities have updated their zoning codes to make ADUs a legally permissible use. Despite this trend, ADUs remain a small fraction of the new housing units built in most communities each year.

This guide is intended to help community leaders, planners, and housing practitioners and advocates take concrete steps to overcome specific barriers to expanding the local supply and legal occupancy of ADUs. Each discussion of potential solutions to a specific challenge includes references to resources that provide supporting information or more extensive guidance.

AARP and APA's ADU Collaboration

AARP works on multiple fronts to help communities become more livable, including encouraging programs and policies that expand housing options and increase housing affordability to help people remain in their homes as they age. AARP's efforts on ADU policy support these goals. APA is focused on promoting effective planning that creates communities of opportunity for all. Housing and zoning reform is a critical area of concern. APA believes that reforming codes and empowering planning are essential elements of addressing the nation's housing challenges and meeting today's social, economic, and equity challenges.

AARP and APA's collaborative focus on ADUs dates back more than 20 years. In 2000, the AARP Public Policy Institute published a model state act and local ordinance for ADUs drafted by APA staff members (Cobb and Dvorak 2000). More recently (2018), AARP and APA conducted parallel surveys that shed light on individual and community experiences with ADUs. Then, in December 2018, AARP and APA jointly convened a group of ADU experts to define the work and policies needed to advance and improve the use of ADUs. APA participated in the effort led by AARP to update the model legislation. This vital new resource, AARP's ADU Model State Act and Local Ordinance, was released in early 2021. AARP and APA are also collaborating on an upcoming review of ADU state legislative activity and trends.


Page Count
Date Published
May 26, 2023
Adobe PDF
AARP Livable Communities

About the Authors

David Morley, AICP
David Morley, AICP, is a Research Program and QA Manager at the American Planning Association in Chicago, where he manages and contributes to sponsored research projects; manages the development of the Research KnowledgeBase; develops, organizes, and participates in educational sessions and workshops; and writes for APA publications. Mr. Morley also edits Zoning Practice.

Shannon Guzman
Shannon Guzman is the director, housing and livable communities with the AARP Public Policy Institute, where she is also the deputy of the enterprise Housing Issue Area and works on housing and livable communities policy. She provides policy analysis and guidance and develops resources to inform community members and assists local decision makers in their efforts to support residents who want to age in place. Guzman has presented on livable communities and housing policy solutions to various audiences across the country and has been quoted in local and national media. She has co-authored publications on housing, universal design, ADUs, community livability, and transportation. Before joining AARP, Guzman was a senior planner in Maryland.

Table of Contents


How to Use This Guide

AARP and APA’s ADU Collaboration

ADU Basics

Common Barriers

Overcoming Political Barriers

Challenge 1: Lack of Understanding

Challenge 2: Lack of Inclusivity

Challenge 3: Local Intransigence

Overcoming Regulatory Barriers

Challenge 1: Few or No Permissible Locations

Challenge 2: Overreliance on

Discretionary Approvals

Challenge 3: Overly Restrictive

Zoning Standards

Overcoming Procedural Barriers

Challenge 1: Inexperienced Applicants

Challenge 2: Uncertain Processes

Challenge 3: Illegal Units

Overcoming Financial Barriers

Challenge 1: Planning and Design Costs

Challenge 2: Construction Costs

Challenge 3: Development Fees and Charges