Roofs

Wood shakes treated with a pressure-impregnated, fire-retardant chemical can achieve a Class A assembly rating. In California, wood shakes treated with a fire retardant must pass a natural weathering exposure test to be approved for use by the Office of the State Fire Marshal (OSFM). Wood shakes approved for use in California must be registered with the OSFM Building Materials Listing Program. In some communities within and outside of California, wood shakes and shingles treated with fire retardants are not allowed.

A complex roof provides an additional level of vulnerability. The term complex indicates that there are a number of horizontal- to-vertical intersections on the roof that could make a Class A roof more vulnerable to wildfire, and in particular to an ember exposure. From a fire performance perspective, these intersections provide collection points for windblown debris (e.g., pine needles and other vegetation), debris from overhanging trees, and—during a wildfire—windblown embers. These locations are also where different construction materials with different fire vulnerabilities will be present on the respective surfaces. If ignited, the flames from the burning vegetative debris would provide a flame contact exposure on the siding material, the roof sheathing or soffit material, or even a window. The vulnerability of these components will depend on material selection and other design considerations. Particularly with a Class A roof, it will be the fire resistance of the siding, sheathing, or window that will determine the vulnerability of the complex roof, not the roof covering itself.

SKYLIGHTS

Skylights typically cover a small portion of the roof, but they can still provide an entry point for wildfire. Flat skylights contain tempered glass. Domed skylights have a plastic outer shell, usually with an inner layer of flat glass. In domed skylights that can be opened (i.e., they are operable), screening is sometimes used instead of the flat glass layer.

If you have an operable skylight, make sure it is closed during a wildfire in order to avoid the entry of burning and glowing embers. None of these configurations could pass a standard Class A fire exposure test used to evaluate roofing materials. To understand the potential vulnerability of your skylights, you should consider the slope of the roof, the location of nearby combustible materials, and the location of accumulated debris on and around the skylights. If your roof has a steep pitch, the skylight would receive more radiant heat from nearby burning vegetation or buildings, and glass may break or plastic deform. As always, it is better to keep debris cleared away from the skylight. Normally debris will not accumulate on the domed skylights, but it can on the flat skylights, particularly on lower sloped roofs. Debris can also accumulate at the edge of skylights. If that debris were to ignite, then the materials and connections at the roof-to-skylight intersection would be vulnerable, so it is important to clear debris on a regular basis. Vegetation management should also be part of your solution. Overhanging tree branches should be removed since a broken branch could fall and break the skylight.

ROOF EDGES

The roof edge is vulnerable to wildfire exposures in two ways. The first is when you have a debris-filled rain gutter located adjacent to the roof edge. The second occurs with roofing profiles where the design results in large gaps between the roof covering and the roof sheathing. A common example of this is barrel-design clay tiles. The gaps typically occur at the roof edge, but can also occur at the roof ridge (peak). In both, an ember exposure would be the most important ignition source.

RAIN GUTTERS

When ignited by embers, the burning debris in the gutter will provide a flame contact exposure to the edge of the roof. The protection provided by the roof edge must be sufficient to resist the entry of flames into the attic space or cathedral ceiling. The roof edge must also protect against the ignition of the exposed roof sheathing or the exposed fascia board. The exposure is more severe if metal angle flashing is not used at the roof edge and if the gutter is hung below the roof edge, leaving the roof sheathing exposed.

The most important thing you can do for the gutter is to keep it clear of debris. This debris can be readily ignited by embers during a wildfire.  The material that the gutter is made from is less important.  A metal (noncombustible) gutter will stay in place while the debris burns and the resulting flames will impinge on the edge of your roof (not your Class A roof covering, but the edge of it).

The vulnerability of the roof edge will depend on materials used and how well the flashing if used, protects the edge. On the other hand, a vinyl (plastic) gutter will quickly melt, detach, and fall to the ground (Jennings 2000). The burning debris will fall with it and continue to burn on the ground. Once on the ground, the roof edge is no longer exposed to flames, but combustible siding may be, particularly if the near-home vegetation or ground cover can easily ignite. The problem with gutters is that the debris can accumulate in them. Keep debris out of them, and the problem goes away. Inspection and removal of debris in gutters should be done before fire season and as necessary thereafter. Since debris, just like burning embers, can be blown in from surrounding areas, a good vegetation management ( fuel reduction) plan around your property can reduce, though not eliminate, the accumulation of debris in gutters. A pre-evacuation task that would alleviate the problem of some debris accumulation in a gutter would be to plug the downspouts and fill the gutter with water. The downspouts would be uncovered upon returning home.

Given the potential problems with gutters, why not just do away with them? Properly installed and maintained gutters and downspouts play an important moisture-management role for a building by collecting and moving water to where it will not have a negative (moisture- related) impact on the foundation and crawl space. (A properly installed subsurface drainage system, however, could alleviate the need for gutters.)

A number of gutter cover devices are commercially available. These products are intended to limit the accumulation of debris in the gutter and allow for the free flow of water into and out of them. These devices either cover the gutter with a solid material or screen or fill the gutter with a porous (foam) material. There is variability in the cover devices, including those that 1) incorporate a screen that completely covers the gutter, 2) incorporate a solid, thin metal sheet that covers the gutter but has an opening at the outside edge to allow water to enter, or 3) use a hybrid metal cover/louvered design. The solid, thin metal cover relies on the surface tension of water, releasing from the rounded metal edge of the cover to drop into the gutter. The porous foam devices allow water to enter and flow through the gutter while excluding debris larger than the pores. A procedure to evaluate the performance of these devices has not been developed, so if you are consider- ing one of them, review the available literature that represents a range of designs and look at devices installed on nearby homes. The devices require maintenance – with some there is a tendency for debris to accumulate on the roof behind the device, which you should remove. None of the available devices is likely to be completely maintenance-free.