900 East Main Street, Suite 109

Grass Valley, CA 95945


1250 East Ave #10

Chico, CA 95926



500 ADU Rendering

Is there a minimum or maximum size my ADU can be?

Recent State legislation has addresses size limitations for ADUs. The State legislation allows for efficiency units that can be as small as 150 SQFT and units as large as 1200 SQFT (with stipulations) and 800 SQFT (with fewer stipulations).

It should also be noted that State legislation does not define what constitutes the SQFT. Local jurisdictions are currently deciding how this area is calculated. These can range from allowing 800 SQFT of conditioned space plus covered porches, 800 SQFT of conditioned space and covered porches combined, or 800 SQFT of conditioned space plus certain covered porches to be combined. Additionally, garages/car ports can be included in this total are or can be separated out and local jurisdictions have their own maximum SQFT for garages and carports.

What are the stipulations for building an 800 SQFT unit?

State legislation mandates at least an 800 SQFT detached unit can be permitted as long as the height, setback, and parking requirements are satisfied. Attached units are further restricted to 50% in size of the primary unit. Local jurisdictions can allow larger (up to 1200 SQFT with the same height, setback, and parking requirements). Local jurisdictions can also require the ADU to match certain architectural aspects of the primary residence.

What are the stipulations for building over 800 and under 1200 SQFT?

State legislation allows local jurisdictions to require other items to be satisfied if building in this range. These requirements may include lot coverage restrictions, certain floor area ratios to be met, minimum lot sizes, or the ADU to be a certain percentage in size of the primary unit. Additionally, local jurisdictions can limit the size of an ADU to 850 SQFT if the ADU has 1 bedroom or less and 1000 SQFT if the ADU has 2 bedrooms or more.

As noted above, local jurisdictions can allow up to 1200 SQFT units with the same stipulations as the units up to 800 SQFT and attached units are restricted in size to 50% of the primary unit.

I have an existing, unpermitted garage that does not meet the 4’ minimum setback requirements; can I convert to a legal ADU?

In short, yes. Existing structures can be converted to ADUs and so long as the conversion occurs within the same footprint, location, and dimensions of the existing structure, lesser setbacks will be accepted.

Is solar required on my ADU?

There are 4 different scenarios for an ADU construction type with regards to the energy code. These 4 types are shown in the figure below. You can convert existing attached or detached unconditioned space to an ADU, or you can build a new attached or detached ADU. It is the Newly constructed, detached ADU that will require solar. The others are viewed as additions.

Figure 1- Energy Code description of various ADU Layouts. (Fig 9-2 ADU Types from the 2019 Residential Compliance Manual)

I see the rear and side setback is 4’, what is the front setback and required distance to existing structures?

Both these items are determined by your local jurisdiction. The front setback can be found in your local zoning ordinance. The distance between structures varies by jurisdiction and by structure type. Many jurisdictions are allowing ADUs to be placed with a 5’ setback to an existing home, while others require up to 10’.

What are impact fees and how can I avoid paying those?

Impact fees are one way many local jurisdictions raise money to fund the maintenance and development of shared infrastructure. Some common fees include those improving/upgrading:
  • Drinking Water Systems
  • Wastewater Systems
  • Traffic Systems
  • Fire Departments
  • Parks
  • Jurisdictional Wide Facilities

With new State laws, local jurisdictions cannot charge impact fees for ADUs less 750 square feet.

How can I get started with my ADU project?

First, you’ll want to determine what size ADU you can have on your property with the various setbacks and any other physical constraints. You’ll also want to determine what architectural features you’d like with your DU and if your local jurisdiction will require an Architectural review. Once these criteria are met, you are ready to begin designing! Here at Jackson & Sands Engineering, we are happy to assist with these steps. We also have many predesigned units that will greatly reduce your time line in getting to construction.


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