Upgrade to Noncombustible Decks, Porches, Fences, and Sheds

05/03/2023

Why do they matter?

Attachments to your home, such as decks, porches, fences or sheds, can act as fuses or fuel bridges for a wildfire, particularly if constructed from flammable materials.  

What do I need to know?

• Embers, firebrands, and hot gasses can become lodged or trapped at the following places: under decks and other attached structures, where the structures attach to the home, in between board decking, against exterior walls, and at railing edges.
• Consider attachments of your home part of your home. Attachments include any additional structures attached such as room pushouts, bay windows, decks, porches, carports, and fences. These features are often very vulnerable to convective exposures.

Where do I start?

Fences and walls

• Build fences and walls with noncombustible materials, and note that the shape, size, and materials used provide different levels of protection or risk in a wildfire. At the least, ensure that any combustible components are at least 10 feet from the building to prevent heat and flames from igniting the building.
• Typical fencing and wall materials are wood, plastic, composite, metal, wire, concrete, stone, and masonry. Wood is the most combustible, and concrete, stone, and masonry are noncombustible. Softwoods and preservative treated pine are combustible, while dense hardwoods such as red oak and others are more fire resistant. Plastic fences provide better fire resistance, durability, and often strength than wooden fences, but they can melt. Metal fences are more fire-resistant than plastic fences; however, under certain conditions, a metal fence can also act as a horizontal ladder fuel. Concrete, stone, or masonry are the most effective at minimizing the potential for damage to a building from a wildfire.
• Avoid fences with gaps because airborne firebrands can become trapped in the gaps and ignite the fence.
• The common wooden post-and-board fence can become fuel for a wildfire, especially old, weather-beaten fences, and collect embers and firebrands, acting as a horizontal ladder for fuel. If you attach an all-wood fence to your home, use masonry or metal as a protective barrier between the fence and the house. 
• Maintain your fence or wall, and clear any combustible debris near your fence or wall regularly. Also consider the type of landscape vegetation used, as unmanaged landscape vegetation can increase the likelihood that a fence will ignite. See Landscaping article for more information.
• If you build a trellis, use non-flammable metal and cover it with high moisture, fire-resistant vegetation. 

Decks

• Decks are often built at the top of a slope, which is at a high risk of ignition. Consider building and deck orientation to reduce the risk of exposure to a wildfire.
• Decks built with dimensioned lumber are combustible and can ignite quickly.
• Prevent combustible materials and debris from gathering beneath a patio deck or elevated porches; screen underneath or box in areas below the deck or porch with wire mesh no larger than 1/8 of an inch.
• Surround any attached structure with noncombustible material such as gravel, brick, or concrete pavers to prevent vegetative growth and reduce fuel in a wildfire.
• For decking and stair treads, use exterior fire-retardant-treated wood, minimum 3-inch nominal thickness, or brick or concrete pavers and a suitable drainage mat over wood decking or metal grates, or light, poured concrete.
• For existing decks, replace combustible materials with noncombustible or fire-resistant materials.
• Replace dimensional timber railings with fire-resistant materials such as metal, tempered glass, cables, or 3-inch nominal thickness fire-retardant-treated wood.
• Construct deck skirting using fire-resistant or noncombustible material such as fiber-cement boards, and/or construct a patio on the ground around the deck, stairs, or ramp.
• When there is no skirting, install a soffit at the underside of balconies, decks, stair landings, or ramps.
• Maintain decks and other attached structures by replacing deteriorated components before they lose their fire-resistance.

More Resources:

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