Accessory Dwelling Unit Planning and Development


Changes in state law in recent years have increased the potential for Accessory Dwelling Units (ADUs) to support increased housing supply.  New laws have addressed barriers to their implementation at scale, for example: setting development criteria for ADUs, streamlined processing, and limiting impact fees. Implementation of state law requires updating local ordinances, estimating ADU capacity when used to address regional housing need allocations (RHNA) in housing element updates, and a housing element program to incentivize and promote ADUs that can be offered at affordable rents. 

SCAG is funding a variety of ADU support activities as described below, including several with REAP funds for subregions, local governments and housing stakeholder partnerships. It is anticipated that adoption of common practices and tools, particularly within subregions, will accelerate ADU development, have potential to contribute significantly to addressing RHNAs, generate new housing at more affordable levels, foster streamlined permit processing, and offer homeowners a source of income. 

REAP Subregional Partnership Program ADU Projects

SCAG Regional Accessory Dwelling Unit Affordability Analysis 

As cities prepare site inventory analyses for the 6th Housing Element Planning Cycle, the last step in the process allows cities to determine whether the housing element demonstrates sufficient land suitable and available for residential development to meet the jurisdiction’s Regional Housing Needs Allocation (RHNA) for each designated income level or if further program actions are required to accommodate a shortfall. Government Code section 65583.1 details how jurisdictions may consider alternative means of meeting RHNA beyond vacancy and underutilized sites. The potential for accessory dwelling units (ADUs) or junior accessory dwelling units (JADUs) is one of these available alternative means. A jurisdiction must include an analysis of the anticipated affordability of ADUs in order to determine which RHNA income categories they should be counted toward.    

SCAG conducted this analysis in order to provide local governments in the region with assumptions for ADU affordability that can be used to assign ADUs to income categories for the purpose of Sixth Cycle Housing Elements. Affordability can be determined in a number of ways. This analysis examines current market rents for reasonably comparable rental properties, using platforms such as Craigslist, Zillow, and Westside Rentals and key words to identify units that appear to be ADUs1. The analysis relies on a survey of rents of 150 existing ADUs conducted between April and June 2020. Efforts were made to reflect the geographic distribution, size, and other characteristics of ADUs across the following counties/subregions2. For example, LA County is separated into two categories in order to better account for the disparities in housing costs between coastal and inland jurisdictions. 

SCAG Regional Accessory Dwelling Unit Affordability Analysis 
6th Cycle Housing Element Update Technical Assistance – ADU Affordability Analysis 

Housing Element Parcel (HELPR) Tool  

The Housing Element Parcel (HELPR) Tool, released in December 2020, allows rudimentary site analysis for ADUs. This tool will be updated in Spring 2021 (version 2.0) with an ADU Potential Dataset being developed in collaboration with the Urban and Regional Planning Department at Cal Poly Pomona (CPP). The dataset is based on parcel-level land-use relevant sources.  Similar to other pre-selected filters in HELPR, users will have the capability to reconfigure values and dynamically combine it with other filters (e.g., environmentally sensitive areas, opportunity areas, environmental justice areas, etc.). 

 Trending: Accessory Dwelling Units within the SCAG Region 


Other Resources