It is the debris that accumulates in gutters that poses one of the greatest wildfire vulnerabilities for a building. If embers generated during a wildfire ignite debris, such as the pine needles shown in the photo below, the resulting fire will provide a flaming (flame impingement) exposure to the edge of the roof.
It is important to routinely clear debris from your gutters.
Given this amount of debris accumulation, the ability of the ‘roof’ to resist this exposure won’t depend on the Class A, B, or C fire resistance rating of your roof covering. It will depend on the edge of roof – its detailing and materials.
This demonstration (photo below) shows the vulnerability of the fascia-roof sheathing interface. Construction consisted of a nominal one-inch fascia attached directly to 2x rafter tails. ˝-inch plywood sheathing extended over the fascia. Metal angle flashing was used on the outside 12-inches of the soffit assemble. Flashing wasn’t included in the mid-section. Wood wool (excelsior) was used to simulate debris. A burning ember was simulated by a stick match.
As seen in the photograph below, the fire in the gutter ignited combustible material in the enclosed soffit. Flame penetration occurred in the mid-section where edge protection was missing. Small amounts of ‘wood wool’ (excelsior) were attached to the inside surface of the fascia board to simulate attic debris.
The angle flashing used here (photo below) will help protect the roof edge, in the case that these pine needles ignite.
Narrow overhangs are considered to be a ‘safer’ design from a wildfire perspective, but with open-eave construction, combined with a debris-filled gutter, it is more vulnerable than the same scenario but with a wide overhang. With an unprotected edge, the likely path to the attic would be along the roof sheathing. With a narrow overhang, this distance would be shorter. Once fire reached the attic, the home will usually be completely destroyed.
Below is an example of a gutter that has an integrated angle flashing (the gutter and angle flashing are one piece). Similar to the separate angle flashing, this design provides much better protection as it covers both the fascia and roof sheathing.
The use of gutter covers has become more common recently. The purpose of these covers is to help keep vegetative debris out of gutters, thereby allowing water to flow off the roof, into the gutter and to then into and down the downspout. To the extent these devices work, they will also reduce the potential for damage from a wildfire.
There are currently more than 20 commercially available ‘gutter cover’ devices (a web search on ‘gutter covers’ will hit most of them) that claim to minimize accumulation of debris while still allowing water to enter. There isn’t a standard procedure to evaluate performance and there isn’t an independent evaluation of all product types. All will require some routine maintenance.
Commercially available types: 1) open cell foam fill, 2) mesh cover, 3) solid metal cap (not shown), and 4) combination screened & metal covering.
As shown in the photos, ‘gutter cover’ material can be metal or plastic.
The photo below shows a section of a combination-type gutter cover, consisting of a solid metal cover (near the roof edge) and screen (near the gutter lip).
Rolled mesh is the least expensive option. Using wire to attach mesh to the gutter support will help it stay in place.
Use rolled mesh to make a down spout insert, as shown below.
In the photo below, the gutter screen stopped debris from accumulating in the gutter, but resulted in debris accumulating on the roof covering. This is an example of an asphalt composition shingle roof covering, which is a ‘stand alone’ Class A covering. A Class A covering should be able to handle the exposure that would result should this debris ignite via an ember exposure (see the roof module for more details regarding fire ratings for roof coverings).
However, instead of routinely cleaning debris out of your gutter, you should now clean off your roof on a regular basis.
The photo below shows an example of debris accumulation on the roof instead of the gutter. The roof should be kept free of debris.
Chapter 7A of the California Building Code states that ‘roof gutters shall be provided with the means to prevent the accumulation of debris.’’ ‘Prevent’ will be hard to accomplish, but the intent is to minimize the accumulation of debris.
Note that Chapter 7A of the California Building Code doesn’t restrict gutter material – metal or vinyl would be allowed. Why is this? As an example, assume metal and vinyl gutters with similar debris loading. The debris is both gutters is ignited by embers. With the metal gutter, the gutter will stay in place, and the ignited debris will expose the roof edge until all the debris is consumed. With a vinyl gutter, the gutter will likely detach and fall to the ground. The ignited debris will burn out, exposing ground vegetation, and potentially combustible siding. Therefore Chapter 7A is concerned mostly about the accumulation of debris.