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68℉Reducing Fire Risks for ADUs
Actions that reduce the risk of fire in or around your ADU
The Bureau of Fire Prevention has compiled this information to help you understand and reduce the common risks of a fire in or around an accessory dwelling unit (ADU). This guide supplements the Fire Requirements webpage that addresses ADUs.
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Photo: A minimum 3-foot clearance from the property line or fence to the outer edge of the rooftop eaves gives firefighters the access they need in case of a fire or emergency.
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There are several reasons to give fire risk extra consideration:
- If located in the backyard, an ADU is more challenging to access by firefighters.
- A fire in an ADU can easily spread to fences, neighboring structures, and the main home.
- ADUs may be inhabited by elderly or disabled persons who may not be able to move quickly or take necessary actions.
In the table below, we describe the California Fire Code (CFC) requirement and the risk level for a fire that results by not complying with the code.
The Mitigation Actions are the steps that significantly reduce these fire risks. These actions help . . .
- keep a fire contained to the room of origin;
- prevent spread of the fire; and
- prevent a larger fire that would require the use of much water and major response by Fire personnel.
Mitigation actions can be "Active" or "Passive." Active means the action will extinguish or contain the fire. Passive means the action will prevent the fire from expanding beyond the building of origin and/or will facilitate firefighter access for faster response.
Let's look at the codes, evaluate the risks, and figure out actions you can take to mitigate the situation:
| CALIFORNIA FIRE CODE AND THE RISK OF NOT COMPLYING |
TYPE OF RISK | LEVEL OF RISK |
MITIGATION ACTIONS YOU CAN TAKE |
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1. Is the distance from any street, road or accessible point by firefighting trucks/equipment to all points of the proposed ADU no greater than 200 feet, which is the standard length of a hose line? If not, it will take a longer time to respond. Fire personnel will need the time to connect multiple hoses. The delayed response will increase the risk of fire spreading. |
Fire Spread | Moderate |
Active: Fire sprinklers Passive: Fire rated construction for walls, roof, windows, etc. |
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2. Is there a 3-foot clear path available between property lines and all exterior walls of the ADU, including eaves? If not, being closer to a property line will increase the risk for a fire spreading to (or from) nearby structures. Lack of access on any one side of the ADU means firefighters cannot fight the fire from all sides. |
Fire Spread | Severe |
Active: Fire sprinklers Passive: Fire rated construction for walls, roof, windows, etc. |
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3. Is the property accessible by heavy firefighting trucks/equipment? This is mostly applicable for rural and Wildland Urban Interface (WUI) areas. Limitations such as steep slopes, narrow bridges, or other access limitations present challenges. If the property is not easily accessible, this will delay or prevent firefighters from reaching the site. |
Fire Spread & Life Safety |
Severe |
Active: Fire sprinklers Passive: Improve fire access roads; modify passage barriers; use WUI construction techniques; construct defensible space |
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| 4. Are all points of exterior walls of the ADU within 600 feet of nearest fire hydrant? If not, the farther distances to a hydrant will result in greater time needed to bring water to the fire site. |
Water Availability | Moderate |
Active: Fire sprinklers Passive: Fire rated construction for walls, roof, windows, etc. |
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5. At the closest hydrant, is there an available flow of 1,000 gpm at 20 psi? If not, the lack of this water supply and pressure means it will take extra time to establish a water supply from further out. |
Water Availability | Moderate |
Active: Fire sprinklers Passive: Fire rated construction for walls, roof, windows, etc. |
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6. Is the property in a WUI area? |
Fire Spread | Severe |
Active: Fire sprinklers Passive: Use WUI construction techniques; construct defensible space |
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Let's look closer at some of these Mitigation Actions and issues:
Sprinkler systems
A sprinkler system is considered an active action because it will extinguish or contain the fire within the building and will slow the creation of smoke. Add some details about how sprinkler systems work.
Fire-rated construction
Fire-Rated walls, windows and roofs are passive actions that can greatly help prevent a fire from spreading by containing the fire within the ADU. The window, wall and roof materials are designed to withstand flames and the fire's heat.
Wildland Urban Interface (WUI)
If your property is in the Wildland Urban Interface (WUI) — the parts of San Jose that are within large open spaces — there are particular risks to consider. You will want to use fire-rated construction techniques that contain the fire within the ADU. You'll also want to create defensible space:
- Defensible Space: Clearing the space around a building of any dry and dead vegetation that can easily ignite.
Practicing fire safety
No matter whether you're building an ADU for family or as a rental, you'll want everyone on your property to understand life-saving practices associated with fires. Make sure everyone knows where to find and how to use a working fire extinguisher. Practice a fire drill at least annually with all who reside on your property. Learn more at fire extinguisher webpage.
contact
If you have questions about this information, please contact Bureau of Fire Prevention staff at 408-535-7750.