Wildland Urban Interface Code FAQ

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.1 / CRC R327.5

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 fire stopped 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 R327.8

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: Ignition-resistant materials are those tested by a facility recognized by the SFM or ICC-Evaluation Service to have a flame-spread rating not over 25, and comply with accelerated weathering tests.

Eaves and porch ceilings CBC 707A.4, A.6 / CRC 327.7.4. R327.7.6

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 R327.8

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 eaves are fire sprinklered, or vent is 12 feet above a walking surface or grade below.

Windows and exterior doors. CBC 708A / CRC R327.8

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 R327.9

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 if they are ignition-resistant and pass performance requirements specified by the State Fire Marshal.

Underfloor and appendages. CBC 707A.8 / CRC R327.7.8

Exposed underfloor, 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.