Replace Non-Metal Vent Materials

05/03/2023

Eaves, fascia, and soffits are vulnerable to wildfires. Protect these building components to prevent a wildfire from entering your home.

What do I need to know?

Eaves, Overhangs, and Soffits

• Overhangs and the top part of exterior walls can trap windborne embers, convective heat, and radiant heat, so build overhangs and walls with noncombustible or fire-resistant materials.
• Eaves, overhangs, and soffits are not usually constructed with fire-resistant materials, but these are critical components of the home and can spread fire onto the roof, into the attic, or onto and through the exterior wall. Metal panels, untreated wood panels, and vinyl panels as soffit materials are vulnerable to wildfire damage.
• Eaves, fascias, and soffits should be enclosed with noncombustible materials to reduce the size of the vents or openings to prevent firebrands from entering the structure.
• Do not use polyvinyl chloride (PVC) and vinyl siding as they do not provide adequate protection and can melt in a wildfire. And although some vinyl will not burn, vinyl soffits have melted in past fires and allowed embers into the attic space.
• Do not plant combustible vegetation under eaves and overhangs.
• Cover the fireplace chimney, the attic, eaves, and the underside of above ground decks with non-combustible screening with a mesh no greater than 1/4 inch.
• Ensure that your gutters, eaves, and roof are clear of debris.

Guidance for new buildings

Consider a home design without overhangs, or with minimal overhang, to avoid the potential fire risks with soffits and the potential for trapping embers and hot gases. If such a design is not possible, take the following measures:

• Use minimum 1-hour fire-resistance rated soffits to prevent embers and hot gases from contact with the joists, rafters or trusses, or the underside of the roof decking
• Use flat, horizontal soffits instead of attaching the soffits to the sloped joists.
• Use noncombustible or fire-resistant materials for the fascia.

Guidance for Existing Buildings

• Install a soffit under open overhangs
• Check the fire-resistance of your existing soffits and replace those that are not fire-resistant. Some existing soffits (ex: plywood) can be covered with a noncombustible or fire-resistant material (ex: fiber-cement board or stucco).
• In very high fire severity zones, install exterior 5/8-inch fire-resistant gypsum board between the existing and new soffit materials for increased fire resistance.
• If the fascia is combustible, cover the fascia board with a noncombustible or fire-resistant material (ex: fire-retardant-treated lumber, fiber-cement board).

Vents

There are various types of vents in a home: vents for attics; ventilated cathedral ceilings; crawlspaces; and heating, ventilation, and air conditioning (HVAC) systems. FEMA P-737, Home Builders’ Guide to Construction in Wildfire Zones provides additional details about the operation of vent systems and specific wildfire-resistance guidance for each type of system.

During a wildfire, embers and hot gasses can enter vent openings and attic spaces, crawlspaces, and ductwork, spreading fire to the interior of your home. Debris that has gathered at vent openings can also catch fire.

Guidance for New Buildings

• Use noncombustible material for all vents, with a preference of metal for vents and vent flashing.
• At all vent openings, install corrosive-resistant, metal mesh screens with a maximum opening of 1/4 inch.
• Install vent openings with a maximum net free area of 144 square inches
• All vent openings should be at least 10 feet from other buildings or property lines.

Guidance for Existing Buildings

• Replace any non-metal ridge vents or wall louvers with metal vents.
• Install metal screens if existing vent openings do not have screens or if the screen openings are larger than 1/4‑inch.
• Install shutters over gable-end vents, soffit vents, crawlspace vents, and wall louvers. However, if the existing wall or soffit is combustible, shutters may not be effective.
• Regularly have debris near or on vent openings, vent screens, and louver blades removed by a professional.
• Limit vegetation near vent openings.
• When a wildfire is threatening, turn off the HVAC system, including exhaust fans. Thermostat-controlled attic exhaust fans may need to be deactivated by tripping the circuit breaker.

Gutters and Downspouts

• Debris (ex: branches, leaves, and pine needles) trapped in gutters can catch fire during a wildfire and then spread fire to the roof.
• Use noncombustible materials for gutters and downspouts.
• Gutters and downspouts are often constructed of plastic, which can melt during a wildfire.
• Install non-combustible leaf guards over gutters. Types of leaf guards include metal-mesh screens and metal hoods that fit into the gutter. Leaf guards may not prevent all kinds of debris from accumulating, so regularly check for debris that may need to be removed and that the leaf guard has not become dislodged.
• Use gutters and downspouts constructed of noncombustible materials (ex: galvanized steel, copper, and aluminum).

More Resources:

• FEMA P-737, Home Builders’ Guide to Construction in Wildfire Zones.
• FEMA. How to Prepare for a Wildfire.
• FEMA. Rebuilding After a Wildfire.