Protecting Decks, Patios, and Porches

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Risk Factors:

Shown is a California Chapter 7A compliant decking product (left) and a non-compliant product (right). Both are wood-plastic composite decking products.

 Are the materials used to construct the deck, patio or porch combustible?

  • Examples of combustible materials include solid wood or wood plastic composite products.

  • Some manufacturers are now incorporating fire retardant chemicals into their products, and fire performance information for many decking products is now available on the manufacturer’s website.

  • Wood decking treated with an exterior fire retardant also is available.

Do you have combustible materials stored under or on top of the area?

Is nearby vegetation well maintained?

  • Combustible materials and vegetation can act as a wick and allow the fire to move to the deck and other building materials, igniting it and other items stored underneath or nearby.

  • This is particularly important for decks when the house or business is sited on a sloped lot.

  • Depending on the type and condition of the vegetation, flame lengths on a slope can reach more than 30 feet, so even an elevated deck can be vulnerable.

 

Steps to Reduce the Risk of Wildfire Damage:

Select the Right Materials:

IBHS supports following the California Building Code  Chapter 7A requirements for decking. Note that the  California requirements only apply to the part of the deck  that you can walk on (including stairs, landing, deck).  It doesn’t apply to the structural support members (posts  and beams). Your deck boards should meet one of the following options:

  1. The deck boards should be made of noncombustible materials (for example, light weight concrete, metal deck boards and / or flagstone).  

  2. Combustible decking materials can be used if they meet the requirements of one of the following:

    1. Materials must be thick enough to be considered “heavy timber”, which means that the deck board must be at least 3 inches thick.
    2. The decking material can meet the definition of “an ignition resistant decking.  
    3. The decking material must meet the minimum energy release rate requirement.

The Flame Spread Index (FSI) for the deck boards must be determined and provided to the Office of the State Fire Marshal. If the FSI is Class C (Class A is the best, Class C the worst) the siding near the deck would have to be made either from a noncombustible or ignition resistant material.

Because of the uncertainties with regard to long-term performance of coatings as a result of weathering, California does not allow the use of coatings such as stains, paints or other surface treatments to provide long term protection from wildfire exposures. Protect your deck by developing and maintaining an effective defensible space around your home, not storing combustible materials under your deck and keeping wind-blown debris off of your deck, including the gaps between deck boards and the area where the deck abuts the house. Maintain a noncombustible strip at the base of the wall in this area.

 

Enclosing an Elevated Deck, Patio or Porch: 

  • To determine if enclosing your deck, patio or porch would be beneficial, consider whether you store combustible materials underneath it, or if your vegetation management plan is inadequate, particularly in the 0- to 30-foot zone.

  • Avoid storing flammable materials on top of or beneath the deck.

  • Providing sufficient ventilation or other means for water to drain out is a critical step in the enclosure process.

    • The national building code standard requirement for a crawlspace is one square foot of venting for each 150 square feet of floor area. Allow at least this much ventilation and maybe more if you are in a particularly wet area. If you do not allow any wood or wood-based structural support members and boards to dry out, fungal decay will become the biggest threat to your deck, patio or porch.

  • Enclosing your deck, patio or porch will not reduce the risk of the top being exposed to embers. For that, the best protection is to keep the surface clear of leaves, pine needles and other vegetative debris.

  • If the house is supported by a column and beam system, and it doesn’t have skirting around the perimeter, add a skirting of a noncombustible material.

  • Remember to provide vents on all sides to ensure proper ventilation. California’s Building Code has taken the lead in developing guidance for wildfire protections. Learn more about how to choose wildfire-resistant decking materials.

 

Installing Flashing:

  • Attaching a metal flashing strip, approximately 18 inches tall, between the top of the deck, patio or porch and the exterior (combustible) siding can create a barrier between exposure to burning debris ignited by embers and flames near the point where the house intersects with the deck, patio or porch.

  • When attaching the flashing, make sure it is tucked in behind the siding where the top of flashing terminates. This will help prevent water from seeping between the flashing and the siding.

  • Alternatively, if you can find a noncombustible siding material with a similar pattern, the lower two or three courses of siding could be replaced.

 

Replacing a Deck, Patio or Porch: