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CalGreen for ADU’s


CalGreen for ADU’s

CalGreen for ADU’s is required for building permit applications throughout the state. We are receiving many questions on this subject and will try to address them in this article.

Accessory Dwelling Units have exploded throughout California. The State of California recently enacted new laws relating to the construction of these small homes. The changes are a result of the critical need for affordable housing. The housing challenges are a result of high real estate prices, housing shortages and the losses from the widespread fires. ADU’s provide a relief for those struggling to survive in this high-cost, but beautiful, state.

The New ADU Laws

Cal Green ADU

     ADU Interior courtesy of Alameda Tiny Homes

ADUs are small freestanding or attached structures that homeowners can build and rent out. Housing experts say they are a way to add more housing to residential neighborhoods without changing their character in the same way that a new apartment building would.

The new law includes the following:

  • Minimum size must be 220 square feet, or as low as 150 square feet if the city has adopted a lower efficiency-unit standard by local ordinance.
  • Maximum size must be at least 850 square feet for attached and detached studio and one-bedroom ADUs and at least 1,000 square feet for two or more bedrooms. In practice, an ADU might be limited to less than these minimum maximums by the application of development standards, such as lot coverage and floor-area ration. But another new provision prohibits the application of any standard that wouldn’t allow for at least an 800‑square foot, 16-foot tall ADU with 4-foot side and rear setbacks.
  • Converted ADUs may now include an expansion of the existing structure of up to 150 square feet for ingress and egress.
  • Attached ADUs are no longer limited to 1,200 square feet — just 50 percent of the existing primary dwelling.
  • Cities now have to approve new detached ADUs with only a building permit (as they do for converted ADUs), without applying any standard except for 4-foot setbacks, an 800-square foot max and a 16-foot height limit.

The following table is published by the California Housing and Community Development (HCD) and includes the specific code sections:

CalGreen ADU Laws

CalGreen for ADU’s

Cal Green ADU interior

ADU Floor Plan courtesy of Alameda Tiny Homes

All ADU’s must comply with the applicable sections of the CalGreen Residential Mandatory Measures. In some jurisdictions such as Santa Rosa and Sonoma County, ADU’s must also include the Tier 1 requirements. However, CalGreen for ADU’s is not at all clear-cut. The CalGreen Code does not specifically address ADU’s. Instead it includes them under “residential construction”.

Building a tiny home on an existing home site is not the same as building a new home on a new site. Yet the code fails to recognize this difference. This is where the complications arise when applying for the CalGreen portion of your ADU building permit.

Does the ADU project have to revisit site storm water run-off? Are whole house fans required? Is electric heating prohibited? These are but a few of the many questions that arise when applying for an ADU CalGreen building permit. Unfortunately there are no clear answers. For this reason it is important to engage a knowledgeable CalGreen consultant for your project.   

CalGreen Checklist for ADU’s

As a minimum you will need to submit a CalGreen checklist with your ADU building permit application. The CalGreen Mandatory Measures checklist should be filled out by a knowledgeable CalGreen consultant. Unfortunately this is not always done. Instead the project architect, or building designer copies and pastes a checklist into the permit set. Typically every box will be checked. This is a mistake that will cost the building owner time and money.

When submitting a CalGreen Checklist for an ADU, any items that are not specifically required should be marked as “Not Applicable”. It takes a specialists in the CalGreen Code to know which items do, and do not, apply to ADU’s. Every item that gets checked costs the owner money. For this reason it is critical to only check those items that are absolutely required. 

Some jurisdictions require a final site inspection by an ICC Certified CalGreen Special Inspector. These include Santa Rosa, Rohnert Park, Sonoma County, Napa County and others. For these projects you will not be able to occupy your ADU unless all CalGreen requirements are complied with. It is critical in these jurisdictions that you have a knowledgeable CalGreen consultant on your team.

At CalGreen Energy Services we are specialists in the CalGreen Code and ADU’s. CalGreen is our only business. If you have a CalGreen question please feel free to give us a call. We are happy to share our knowledge.   

Our fees for a CalGreen Checklist for a typical ADU building permit application are between $200 and $300. The amount of time and problems we can help you avoid is priceless. 

For more info on our checklist prices see our informative article here:

Alameda Tiny Homes designs, permits and builds ADU’s in Northern California. You can learn more about their ADU’s here:

CalGreen Problems

Call us today and let us show you how we can help with your project.


Phone: 707-328-5299

CalGreen Energy Services


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