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Building & Safety
Wildland Urban Interface (WUI) Codes and Standards

Chapter 7A of theCalifornia Building Code (CBC) and Chapter R337 of the California Residential Code (CRC) contain standards associated with the construction of buildings in wildfire prone areas.  These Frequently Asked Questions address many concerns raised by the  WUI standards. The actual code standards should also be reviewed prior to the implementation of any design or construction project in state and local fire-hazard areas. Web resources are also identified for assistance in better understanding the standards and for identification of approved methods and materials that are allowed.


1. How do I determine if my construction project is subject to WUI requirements?

Computer-accessed maps of the fire-hazard severity zones known as State Responsibility Areas (SRA) and the Local Responsibility Areas (LRA) are available at the Zoning counter in the Planning Department. Counter technicians can assist in determining if your project is within the SRA or LRA Zones. These maps are also available through the County's GIS Mapping Application. Enter your Assessor's Parcel Number in the 'value' box. Click "Find it". Click the "Hazards and GeoPhysical" tab at the bottom of the page.  The  WUI requirements only apply to projects in SRA areas.

Note: The Assessors Parcel Number (APN) of the project will be necessary to locate the relevant information. 

2. What projects within SRA and LRA are subject to WUI requirements?

The WUI standards apply  to new buildings of all occupancy types in SRA areas, in addition to the following:

 Santa Cruz County has amended the CA Codes in regards to projects subject to WUI.   Additions and exterior alterations of existing buildings in all SRA  areas must comply, with the exception of replacement siding not exceeding 100 sq. ft., replacement of a broken window or glass door, replacement of an area of roofing not exceeding 100 sq. ft., and replacement of one attic or foundation vent. Also, new U occupancies, such as a garage or workshop, are not exempt from the WUI construction requirements, regardless of SRA areas, size or location on the property. 

3. If the project is subject to WUI, what do I do?

Review all applicable requirements of CBC Chapter 7A or CRC R337 with your architect, engineer or design professional. Plan reviewers and the Supervising Building Inspector are available to answer technical questions. These code requirements are uniform California standards developed by the Office of the State Fire Marshal (OSFM). Additional information of approved materials, SRA maps and informational publications are available at the following web links: 

4. What are the typical construction requirements associated with WUI?  

The basic requirement is that the exterior of the structure be ignition-resistant and be able to resist the entry of flying embers and fire radiation during a wildfire.  Various building components addressed in WUI are:

Roofs and roof edges.   CBC 705A / CRC R337.5

A noncombustible (tile or metal) or Class 'A' roofing assembly is required in SRA - Very High Fire Hazard Severity Zones. All other areas in Santa Cruz County require a Class 'B' minimum roofing assembly, including LRA, SRA-Moderate or SRA-High areas. 

Where the roof profile allows a space between the roof covering and the roof decking, the spaces shall: be constructed to prevent the intrusion of flames and embers; be firestopped with approved materials; or have one layer of No. 72 cap sheet installed over the combustible decking.
Where provided, valley flashing must be not less than 26 gauge galvanized sheet metal over a 36-inch wide No. 72 ASTM cap sheet.

Exterior Walls/siding.  CBC 707A.3 /CRC R337.7.3

Noncombustible, listed ignition-resistant materials, heavy timber, 5/8" Type X gypsum sheathing behind exterior covering, exterior portion of 1-hr assembly or log wall construction is allowed.  The OSFM website (see link above) lists many types of exterior wall coverings that are approved.

Note:  Descriptions of noncombustible, ignition-resistant and heavy timber are found in the CRC and CBC.

Eaves and porch ceilings  CBC 707A.4, A.6 / CRC 337.7.4. R337.7.6

The exposed roof deck under unenclosed eaves and underside of porch ceilings shall be noncombustible, listed ignition-resistant materials,  or 5/8" Type X gypsum sheathing behind exterior covering.

Solid wood rafter tails on the exposed underside of roof eaves having a minimum 2" nominal dimension may be unprotected. 

Vents. CBC 706A / CRC R337.6

Attic vents and underfloor vent openings must resist the intrusion of flame and embers or shall be a minimum of 1/16" and maximum 1/8" corrosion-resistant, noncombustible wire mesh or equivalent.  Combustible vents on top of roofs may be covered with this material to comply.  Ventilation openings on the underside of eaves are not permitted, unless a SFM approved vent is installed, or the attic is fire sprinklered. Vents of 1/16" min. and 1/8" max corrosion-resistant and noncombustible wire mesh or equivalent that are.more than 12 feet from a walking surface or grade below are allowed.  

Windows and exterior doors.  CBC 708A / CRC R337.8

Windows must be insulated glass with a minimum of 1 tempered pane or 20 min rated or glass block.
Exterior doors must be noncombustible or ignition resistant material or 1 3/8" solid core, or have a 20 min fire-resistance rating.

Exterior decking and stairs.  CBC 709A / CRC R337.9

Walking surfaces of decks, porches. balconies and stairs within 10 feet of the building must be constructed of noncombustible, fire-retardant treated or heavy-timber construction. Alternate materials can be used of they are ignition-resistant and pass performance requirements specified by the State Fire Marshal.

Underfloor and appendages.  CBC 707A.8 / CRC R337.7.8

Exposed underfloors, underside of cantilevered and overhanging decks, balconies and similar appendages shall be non-combustible, ignition resistant, 5/8" Type X gypsum sheathing behind exterior covering, exterior portion of 1-hr assembly, meet performance criteria SFM Standard 12-7A-3 or be enclosed to grade.

5. What is required for building permit application submittal?

The building permit application and plans must identify whether the new structure is in an SRA or LRA zone and provide sufficient detail to determine compliance with WUI standards. When in SRA, indicate the fire severity zone as determined by parcel number using the County GIS Mapping Application and clicking on the "Hazards and GeoPhysical" tab (after entering the parcel number in the GIS application).

6. What specific inspection requirements are applicable to WUI? 

The building inspector will perform the regular inspections associated with construction of a new structure. Upon completion of construction, the owner will receive certification that the building complies with WUI standards in the form of a finaled Building Permit that will include compliance with vegetation clearance requirements as enforced by the local Fire Agency having jurisdiction.