From Center for Fire Research and Outreach-Builders Wildfire Mitigation Guide-DECKS

Replacing a deck or building new, fire safety and fire resistance is important. We found this guide to building decks at Berkeley Fire Center’s website and want to bring it to your attention.

As you may know, all we do is install Desert Crete fire retardant pedestrian traffic coatings for our clients. It’s Class A and One Hour Rated for fire resistance-the best you can get! Call us for a free estimate on fire retardant decking. Don’t gamble your asset over a cheap deck coating that could ignite and burn! Call Bill at 805-545-8300.

 

BUILDERS GUIDE-DECKS

There are two basic kinds of decks – those that have a solid surface and those that utilize (usually gapped) deck boards over the structural framing. The upper surface of a solid surface deck and the underside of gapped-board deck are shown in this slide.

During a wildfire, decks can be ignited from a surface fire from below and/or ember attack from above. If ignited, the burning deck will present a long term flame impingement exposure to the side of the house, potentially igniting or otherwise resulting in failure of the siding, and/or breaking the glass of a window or sliding glass door. If the decking and/or siding is very combustible, flames could spread to the eave.

Issues:

  • Open frame versus solid surface, membrane deck:
    • Most deck boards used in open framed decks are considered combustible (wood, plastic or fiber-plastic composites).
    • If exterior rated fire-retardant treated lumber is used, then the deck boards are classified as ignition resistant.
    • Most solid surface deck surfaces are noncombustible (concrete, stone, tile, etc.)
  • Flame spread, edge of deck to wall
  • Enclosure of decks
    • horizontal
    • vertical
  • Need for venting if enclosed

This is an example of a solid surface deck, with an occupied space below (in this case, a garage). The surface is usually noncombustible (light weight concrete or stone). In this case, the wildfire threat would be from an ember exposure to the top of the deck. More critical than the noncombustible surface would be debris that accumulates on the deck, and any combustibles stored or used on the deck (such as firewood and furniture).

This is an example of a solid surface deck, with an occupied space below (in this case, a garage). The surface is usually noncombustible (light weight concrete or stone). In this case, the wildfire threat would be from an ember exposure to the top of the deck. More critical than the noncombustible surface would be debris that accumulates on the deck, and any combustibles stored or used on the deck (such as firewood and furniture).

This is an example below of a membrane deck with a wood deck. The wood deck boards are attached to 2 x 4 sleepers that rest on a waterproof membrane that is attached to the sheathing. In this example, the wildfire threat would be from embers igniting accumulated debris on deck, accumulated embers igniting the deck boards, and embers igniting deck furniture. Embers and debris would tend to accumulate at a deck-to-wall area, particularly at an interior corner. If the siding is combustible, it could also ignite.

Depending on how far off the ground the deck is, a surface fire burning up the deck could result in a flame impingement exposure to the structural framing members, and the sheathing.

This is an example of a solid surface deck that is enclosed horizontally on the underside. Sometimes enclosed solid surface decks incorporate vents on the underside to allow for some drying should the top surface develop a leak. Depending on the size and location of the leak, venting may or may not be adequate to dry out the space.

Although some wildfire guides suggest that decks be enclosed, it doesn’t always make sense to do this. If your defensible space requirements have been met, and you aren’t storing combustible materials under your deck, the benefits of enclosing your deck are minimal, and moisture-related degradation issues become more of a problem.

There are two ways that decks can be enclosed: 1) enclose ‘vertically’ using a siding product. The siding would be attached to a framing system integral to the vertical support columns, and 2) enclose horizontally , again with a panelized siding product. The siding product would be attached to the bottom of the horizontal support joists.

In a deck consists of gapped deck boards, either of these enclosure methods would result in water moving into the enclosed areas. Some drainage or ventilation system would have to be incorporated into the design, or fungal decay would soon be a problem. The ‘vertically’ enclosed deck, shown in this slide, has incorporated vents into the design (shown with arrows).

READ THE REST HERE       http://firecenter.berkeley.edu/new_bwmg/decks/issues

 

 

 

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