Preapproved plans cut housing design costs by $10,300

Homeowners building smaller residential projects in California can save an average of $10,300 in design and permitting expenses if they use preapproved architectural plans. A new study from the University of California, Riverside, indicates that these standardized blueprints also reduce the time required to secure permits by roughly 53 days. The findings suggest a practical path for expanding housing stock in established neighborhoods without the high overhead associated with large-scale development.

The research focused on the "missing middle" housing category, which includes duplexes, townhouses, and bungalow courts. These structures sit between single-family homes and large apartment complexes. They often face high costs for architectural and engineering reviews because they lack the scale to negotiate better rates with design firms. Preapproved plans address this by completing technical reviews for structural, mechanical, electrical, and plumbing components before a specific property owner applies for a permit.

The city of Riverside serves as the primary case study for the report. Its City Council approved a new program in June 2026 that offers specific designs for a duplex and a bungalow court. The duplex plan features two units of approximately 1,300 square feet each, with three bedrooms and two bathrooms per unit. The bungalow design is 1,000 square feet with two bedrooms, two bathrooms, and a private patio. Both layouts include a ground-floor bedroom and bathroom to accommodate residents with varying mobility needs.

The study surveyed 89 California jurisdictions, with 59 providing responses. Most respondents reported using preapproved plans for accessory dwelling units, commonly known as granny flats. These communities reported permitting or constructing about 500 ADUs using the streamlined process. Only four jurisdictions offered preapproved designs for housing beyond ADUs, and just one reported permitting such a project, a triplex.

Cost savings varied significantly across the surveyed cities. While the average saving was $10,300, individual reports ranged from a few thousand dollars to $45,000. The study notes that savings for ADUs may not directly apply to larger projects. Preapproved plans do not grant automatic building permission; owners must still satisfy local zoning, parking, utility, and grading requirements. Any modifications to the standard designs may trigger additional review processes.

The Riverside program emerged from discussions in a regional Housing Policy Leadership Academy. The city developed the plans with input from residents and technical advisers. Kristen Kopko, the research manager at UCR's Center for Community Solutions and lead researcher on the study, noted that the approach is particularly useful for cities with vacant land suitable for infill development. She stated that such plans could help fill vacant lots or revitalize areas.

The study, titled "Preapproved Housing Plans for Missing Middle Housing: A Case Study of the City of Riverside," was authored by Kopko, Justine Ross, Jayden Li, and Qingfang Wang. The researchers recommend that cities track how often the plans are used and monitor whether projects reach the construction phase. The next step is to determine if the cost and time efficiencies translate into completed housing units for middle-income households.