{"id":110863,"date":"2026-07-20T11:42:20","date_gmt":"2026-07-20T18:42:20","guid":{"rendered":"https:\/\/www.redfin.com\/blog\/?p=110863"},"modified":"2026-07-20T14:49:56","modified_gmt":"2026-07-20T21:49:56","slug":"what-to-know-before-adding-an-adu","status":"publish","type":"post","link":"https:\/\/www.redfin.com\/blog\/what-to-know-before-adding-an-adu\/","title":{"rendered":"What Homeowners Should Know Before Adding an ADU"},"content":{"rendered":"

Accessory dwelling units (ADUs) have become a practical way to create extra living space without buying a larger property. Whether you’re planning a <\/span>Seattle, WA home<\/span><\/a> for aging parents or a <\/span>Phoenix, AZ rental<\/span><\/a> unit for additional income, an ADU can offer flexibility while potentially increasing your property’s long-term value.<\/span><\/p>\n

Still, building one involves much more than choosing a <\/span>floor plan<\/span><\/a>. Local regulations, site conditions, utility upgrades, and project costs all influence what’s possible. If you’re wondering what to know before adding an ADU, it starts with understanding your property’s limitations, setting a realistic budget, and deciding how you want the space to serve you for years to come.<\/span><\/p>\n

What is an ADU?<\/span><\/h2>\n

An accessory dwelling unit (ADU) is a smaller, independent home built on the same property as a primary residence. Also called in-law suites, backyard cottages, or <\/span>granny flats<\/span><\/a>, these secondary homes typically include their own kitchen, bathroom, and living area. Homeowners often add ADUs to create space for family, generate <\/span>rental income<\/span><\/a>, or add flexible living space while potentially increasing their property’s long-term value.<\/span><\/p>\n

1. Start with local zoning and permitting requirements<\/span><\/h2>\n

Before sketching layouts or comparing builders, confirm what your local government allows. While many states and cities have updated their ADU policies to encourage more housing, local requirements still vary widely. Rules governing setbacks, maximum size, lot coverage, parking, utility connections, and occupancy can differ from one municipality, or even one neighborhood to another.<\/span><\/p>\n

Mycka Koger, Owner of <\/span>Salt to Summit Construction & Renovation<\/span><\/a>, recommends skipping the online searches and going straight to the source. “Before adding an ADU, homeowners should start with their local zoning office, not the internet. ADU rules vary significantly by city even within the same county.”<\/span><\/p>\n

Anna Alekseyeva, Director of the <\/span>ADU Resource Center of San Mateo County<\/span><\/a>, offers similar advice. “Before moving forward with an ADU project, homeowners should familiarize themselves with their local rules and regulations. Get in touch with the permitting staff in your local government agency and ask them if there are any restrictions on what you can build.”<\/span><\/p>\n

When speaking with your planning department, ask about setbacks, height restrictions, parking requirements, utility connections, owner-occupancy rules, and whether short-term rentals are permitted. If your neighborhood has a <\/span>homeowners association (HOA)<\/span><\/a>, review its governing documents as well, since architectural guidelines or design standards may also apply.<\/span><\/p>\n

Starting with accurate, local information can help you avoid redesigns, permitting delays, and unexpected costs later.<\/span><\/p>\n

>> Read: <\/i><\/b>How Do Zoning Laws Affect Your Property?<\/i><\/b><\/a><\/p>\n

2. Complete a feasibility study before choosing a design<\/span><\/h2>\n

One of the biggest mistakes homeowners make is falling in love with an ADU design before confirming their property can actually accommodate it.<\/span><\/p>\n

Daniel Hogenson, owner of <\/span>RenovatePros<\/span><\/a>, says this is where many projects go off track. “One of the biggest mistakes homeowners make is choosing an ADU plan before understanding what their property can actually support.”<\/span><\/p>\n

Every property has unique conditions that affect construction, including zoning, setbacks, utility access, <\/span>drainage<\/span><\/a>, soil conditions, easements, and available building space.<\/span><\/p>\n

The <\/span>Apex Homes Marketing Team<\/span><\/a> recommends beginning with a feasibility study. “Homeowners should always start with a feasibility study to understand what is actually possible on their lot, including zoning, setbacks, utility access, permitting requirements, and budget expectations.”<\/span><\/p>\n

A professional site evaluation can help determine:<\/span><\/p>\n