Navigating ADU Permits and Regulations in 2025
As accessory dwelling units (ADUs) gain popularity across the United States, understanding the permit and regulatory landscape is essential. In 2025, many jurisdictions are making it easier to build these secondary homes thanks to legislation like Washington State’s House Bill 1337, which relaxes restrictions on ADUs and allows multiple units on a single lot. Similar laws are emerging nationwide to address housing shortages and encourage more "middle" housing options, so the overall path to approval is becoming smoother.
Before breaking ground on an ADU, you’ll need to secure the right permits. Local authorities require permits to ensure that your project meets building codes and zoning regulations – and to make sure the finished space counts as livable square footage when you sell or refinance your property. Building codes are not just bureaucratic red tape; they help ensure that any structure you add is safe. Seattle’s HB 1337, for example, lets homeowners build up to two ADUs per lot if they comply with size and safety standards, and other cities offer similar allowances.
The permit application process varies by location, but typically you’ll be asked to submit detailed plans for your ADU project. These include architectural drawings or engineering plans that describe the structure’s size, layout and connection to utilities. Under updated 2025 rules in many states, planning departments must review permit applications within about 60 days, and fees are often reduced for smaller units under 750 square feet. Parking requirements have also been relaxed when a property is near public transit, making urban ADUs more feasible.
Navigating ADU regulations doesn’t have to be overwhelming. Consult your city or county building department early, and consider working with a designer or contractor who understands local codes. With more streamlined permitting timelines and laws aimed at encouraging secondary housing, 2025 is shaping up to be one of the best times to add an ADU and unlock additional value from your property.
