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What to consider for an ADU

There's a handful of things one needs to consider for an Accessory Dwelling Unit, or ADU for short. An ADU is loosely defined as a self-contained dwelling unit which has a Kitchen, Sleeping Area, Bathroom, and it's own dedicated Egress. They are commonly called Granny-Flats, Next-Gen Suites, Casitas, She-Sheds, and Mother-in-law Suites.

Despite the nomenclature it is always Accessory (secondary) to the Principal (main) House, and is either Attached or Detached. In this blog we will give an overview of the main things to consider for an ADU Project!


Types of ADU's

There are two types of ADUs: Attached to the House, or Detached from the House. An Attached ADU is one that can reside anywhere in the home whether it's an Addition or Remodeled to any level of the home. Detached ADUs can be either stand-alone or connected to the Garage or another Accessory Structure, although Above Garages are most common.

Diagrams showing different ADU Types


Design Considerations

As the ADU is a separate second-dwelling unit there are some unique design features to consider in order to provide separation, access, and comfort to the tenants.

  1. Separation is important from a Livability, Energy, and Safety Standpoint. This reduces the risk of fire spreading through the units and minimizes any cross-over between units for smell and noise!

  2. Access is critical for some locations as the Entrance needs to be private and distinct from the main House. There are many ways to handle the access and it will be unique to the Project. A Detached ADU in the Rear Yard may be accessed through the Alley, whereas an Attached ADU may be from the Side Yard.

  3. Comfort is key! While being comfortable isn't a code requirement, it does make the unit more desirable. Think about the privacy, air conditioning and heat, parking, and open space (should tenants have puppers).

Zoning Requirements

While the ADU is considered Accessory, it will face similar limits as building a house. Those limits are going to include questions such as:

  • Is there enough Floor Area to construct the ADU?

  • Are there strict Setbacks, Easements, or Bulk Planes preventing the additional structure?

  • Are the Utilities going to allow for the ADU?

  • Do you have an HOA or Covenant that allows for the ADU?

  • Is there space for vehicle parking?

Building Requirements

Once the zoning is covered it's on to the building requirements, which will be directly related to the type of ADU Project. A Remodel is going to face far less hurdles than an Addition or New Structure would. A new Detached ADU will likely require fire suppression whereas an Attached ADU may not require fire suppression. Some common building related questions include:

  • Is the ADU going to have separate power, heating, water, cooling systems?

  • If an Addition, will the existing structure's foundation support the new load applied?

  • Will you be able to get the existing plumbing and sewer connected for the new bathroom and kitchenette?

  • Does the jurisdiction count the amount of plumbing fixtures for the water tap? An ADU could be adding +7 new fixtures (including Washer, Dishwasher, etc.) to the water tap.

Final Considerations

There are some additional considerations one should make when exploring any ADU Project. These should be researched ahead of time before starting.

  • Consultants such as a Surveyor, Geotechnical Engineer, and Energy Rater may be required for the Building Permit. Any ADU which involves new structure will require a Structural Engineer.

  • Rental Licenses are handled through the local jurisdiction by the Owner. There may be specific rules and requirements to get the License, whether it's short term, long term, market-rate, or affordable.

  • Ownership of the ADU has to have the same Owner as the House and you cannot sell your ADU separately from the property.


Taking on an ADU Project is similar to taking on a mini-house given that it follows similar rules and circumstances. It may be complicated, but it doesn't have to be! The fun of the ADU Design should be in the space planning and interior design. Fortunately we are here to help!

Should you be interested in an ADU Project of your own we'd be happy to help in determining the feasibility and steps involved and offer architectural design!

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