Windborne embers, convective heat, and radiant heat can be trapped under overhangs and in the upper portion of exterior walls. It is important to seal openings, screen or otherwise block areas where debris accumulate, remove combustible items and maintain an ember-resistance zone around the overhangs.

Some basics about Eaves and Soffits

The eave is the part of the roof that extends out beyond the exterior wall.

There are two ways to detail the underside of the eave – the intersection between the exterior wall and the roof. These include ‘boxing-in’ and using open framing (open eave). Other terms for ‘boxing-in’ include a ‘soffited eave’. If you have a ‘soffit’ you have used a ‘boxed-in’ technique. Most homes use an open eave / open framing detail because it is less expensive ‘ you have used an open frame technique if you can see rafter tails, and between rafter tail blocking.

Primary fire risks related to eaves include:

• Windborne embers, convective heat, and radiant heat can be trapped under overhangs and in the upper portion of exterior walls. Overhangs and walls can ignite if not constructed of noncombustible or fire-resistant materials.
• Typical construction materials for eaves, overhangs, and soffits are not fire-resistant and are therefore susceptible to ignition by embers and hot gases.
• Once an eave, overhang, or soffit has ignited, fire can spread onto the roof, into the attic, or onto and through the exterior wall.
• Soffits normally have vents as part of the attic ventilation system. Unprotected vents can allow embers and hot gases to enter the attic.

Wildfire research conducted by IBHS supports the use of soffited-eave construction. Additional research and guidance (e.g., FEMA P-737, Home Builder’s Guide to Construction in Wildfire Zones – Fact Sheet No.6 https://www.fema.gov/media-library-data/20130726-1652-20490-2869/fema_p_737_fs_6.pdf) also suggests a soffited design as the best option. A flat soffit reduces the potential for entrapment of embers and hot gases.  Vents located in the under-eave area can be entry points for embers and flames when limited effort has occurred to reduce risks in the home ignition zones (particularly in the near-home zone). Embers entering an attic can ignite stored combustible materials. Research has shown that open-eaves are more vulnerable to both ember entry and direct flame contact exposures, relative to soffited-eaves.

With open eaves, use a sealant (such as caulking) to cover gaps, or enclose the underside of the roof overhang. In open-eave construction, embers can and do accumulate between blocking and joists and can ignite these members if sufficient accumulation occurs.  A wider eave can be protected from wild fire exposures by using ignition resistant or noncombustible materials for example by stucco that is wrapped around and under the eave.

For a more detailed technical discussion of fire safety relative to eaves and soffits please see https://ucanr.edu/sites/fire/Prepare/Building/eaves/