Accessory Dwelling Units

An Accessory Dwelling Unit (ADU), also known as a "Secondary Dwelling unit", a "Granny unit", or an "In-Law Unit", come in many shapes and sizes but are always a self-contained home that is usually smaller than the main house and legally part of the same property. They must have a kitchen, bathroom, and place to sleep, and can range from small studios to larger homes with multiple bedrooms. ADUs are subject to the development standards and requirements found in Chapter 18.84 of the Municipal Code.

Types of ADUs

There are many types of ADUs, and they don’t always fit neatly into one category:

Detached: New freestanding structure separate from the main home (site-built or prefab/manufactured).
Attached: New structure (may include converted space) sharing at least one wall with main home.
Conversion: Converted existing space in the main home or on the property (bedroom, detached garage).
Junior Accessory Dwelling Unit (JADU): A smaller conversion ADU within the main home or attached garage.
- Up to 500 square feet
- Efficiency or full kitchen
- Can share bathroom with main house (if it’s accessible from the JADU)
- Owner must live on the property

What isn't an ADU?

RVs, tiny homes on wheels, yurts, and storage structures are generally NOT considered accessory dwelling units.

Your Path to a Completed ADU

The following checklists can assist you with answering any questions you may have about your property and building an Accessory Dwelling Unit:

Before applying for a Building Permit, contact a Planning staff member at planning@morganhill.ca.gov to confirm the Zoning designation for the proposed location of the ADU and any additional requirements.

Pre-Approved Accessory Dwelling Unit (ADU) Plans

Access the Morgan Hill ADU Plans Gallery at: morganhill.aduaccelerator.org/gallery.

Look for inspiration
See what’s pre-approved in Morgan Hill
Find a design you want to use
Connect directly with the designer or company
Complete site planning for your property

The Morgan Hill ADU Plans Gallery provides a variety of ADU designs from designers, including pre-approved plans that have been pre-reviewed for building code. Browse and filter to find various ADUs. Once you’ve chosen a design, connect directly with the architect or company to use or purchase the ADU plan before completing site planning for your property.

Note: All plans – even pre-approved plans – still require customized site planning and permitting based on your property. This will include details like where the ADU sits on your lot, emergency access, and foundation plans.

FAQs

What are pre-approved ADU plans?

Pre-approved plans have been pre-reviewed for building code by a local, state, or federal government only. They are general and not tied to a specific property, including structural, roof, and floor plans, and cannot be customized much beyond materials to qualify for the expedited review. Additional review and approval will be required by the Planning Division and Building Division for property-specific elements, including the foundation for the ADU.

Am I allowed to build an ADU?

In almost all cases, yes! ADUs and JADUs are allowed in any single-family or multi-family zone. If residential buildings are allowed, ADUs are almost always allowed too (with limited exceptions). California state law now allows a single-family property to have a JADU, an internal conversion or attached ADU, and a detached ADU. Multifamily properties – like duplexes, triplexes, and apartment buildings – can have up to eight detached ADUs or up to 25 percent of the number of units, depending on your property. Please contact a Planning staff member at planning@morganhill.ca.gov to confirm requirements for an ADU on your property.

What if my property is in a historic zone, hillside, high-fire severity area, flood zone, or another special zone?

Please contact a Planning staff member at planning@morganhill.ca.gov for guidance about building an ADU in special zones. It may require an additional application, or it could significantly limit what you can build on your property – so make sure you ask before you purchase any plans.

What types of ADUs are in the gallery?

All designs are detached ADUs, which are new buildings separate from your main home.

How do I use the ADU Plans Gallery?

The Plans Gallery can help you at various stages of an ADU project. When you’re just getting started, you can browse for inspiration on design, layout, and features. When you have a clearer picture of what you are looking for and what fits on your property, you can select a design and contact the designer or company for more details (inclusion in the gallery does not constitute endorsement of an individual designer or company). We invite you to use the various features of the Gallery, including filtering for construction type, square footage, number of bedrooms, and features important to you. You can also mark favorite plans and return to your favorites later!

What do I do after I pick a design?

You can contact the designer directly and/or access the plans online, then work with the original designer or another professional to complete site planning and file all necessary applications.

How much do plans typically cost?

Designers set the price to use their plans or purchase prefabricated units, and costs can vary based on what is included in the plans.

I am having trouble using the ADU Plans Gallery, what do I do?

Please go to ADUAccelerator.org/docs/homeowners for instructions and helpful articles. If you are still having trouble, please contact support@aduaccelerator.org with a description of your issue.