Wildland-Urban Interface Demonstration Building - Roofing & Gutters

Wildland-Urban Interface Demonstration Building
Roofing & Gutters Vents Eaves & Soffits Windows Siding Near-home

The roof of the demonstration structure has two roof coverings. The covering on this half of the roof is untreated wood shakes. If you are living in a wildfire prone area, and your home has an untreated wood shake roof, replacing it with a Class A covering should be your highest priority “home project.”

See a video demonstration of some issues to keep in mind about roofs and wildfire.

An untreated wood shake roof doesn't even meet a “Class C” rating. A pressure impregnated, exterior rated fire retardant treated shake roof has a “Class B” fire rating by itself (considering only the wood shake covering) or a “Class A” rating “by assembly” (covering plus underlying material). An example is shown here - FR treated shake, plus the underlying gypsum-fiberglass product (the white material) and plywood roof sheathing that provide the Class A rating ‘by assembly’.

One component of the fire test for roof coverings is the “brand” test. “A”, “B” and “C” brands are shown in this photograph. The “A” brand is 12" x 12", the “B” brand is 6" by 6". The “C” brand is about the size of an ice cube. The “A” and “B” brands are constructed using a three-layer construction (the middle layer is perpendicular to the top and bottom layer. Each “stick” is 3/4" x 3/4". The other two parts of the fire test for roof coverings are 1) flame spread and 2) potential for the roofing to generate embers. The covering must pass all three parts.

This is a photograph of a fire test on a fire-retardant treated shake roof (“stand alone” Class B, Class A “by assembly”). The burning “A” brand [12" x 12"] is ignited prior to placing on the roof. The pressure impregnation process, and “post impregnation” heat treatment is required to give the fire retardant the exterior rating. Products that are sprayed on “in-service” haven't been shown to weather well, and therefore aren't sufficiently durable.

Burn through the roof into what would be the "attic" indicates that, as constructed, this roof assembly did not pass the "A" brand roof fire test. Therefore, it doesn't meet the requirements of a Class A roof covering.

1/4" mesh screening is used in the “through-roof” vent shown in this photograph. Depending on materials and debris in the attic, embers that enter through this vent will have sufficient energy to ignite debris. The pine needles that are accumulating between shakes will facilitate ignition of an already readily combustible roof covering. Once ignited, flames will readily enter the attic through the vent opening.

This is an asphalt composition shingle roof covering and has a Class A rating. If ignited, the debris that has accumulated at the entrance to the through-roof vent won't be a problem for the Class A roof, but the resulting fire could result in an ignition in the attic, depending on debris accumulation there.

A fiberglass asphalt composition shingle roof covering was used on this side of the building. It has a Class A “stand alone” rating.

This is a photograph of a Class A fire test on a fiberglass asphalt composition shingle roof. Fire did not penetrate through covering and into the attic during the course of the test.

“Class A” is not the same as “noncombustible”. This fiberglass asphalt composition roof was installed on a gazebo. The asphalt was hot enough to flow, and possibly ignited, when subjected to the radiant energy exposure that occurred when the home on the parcel ignited.

If ignited by embers, the fire from the pine needles won't be a problem for this Class A roof covering (as long as it is in good condition). However, depending on the adjacent siding, the flames may be able to penetrate into the stud cavity and then into the attic, or may be able to directly enter the attic through the gable end vent. If you have a complex roof, as shown in this photograph, make sure the materials adjacent to your Class A roof provide comparable protection from the wildfire. Clean debris off your roof on a regular basis.

Vegetative debris that accumulates in gutters can be readily ignited by embers. If ignited, the flames would impinge at the edge of the roof, not the roof covering. The vulnerably of the roof edge would depend on materials and detailing used there.

In lieu of regularly cleaning debris out of the gutter, a gutter cover could be used to minimize accumulation of debris. There are many types of gutter covers or screens that are intended to keep vegetative debris out while still allowing rain water from the roof to enter. A solid cap / screen cover is shown here. Other options include solid metal cover, 100% screen mesh cover, and foam insert.

This is a photograph of a mock up of a fence - wall - roof eave assembly. Pine needles were placed in the metal gutter, and ignited by placing ignited stick matches in the gutter. Depending on the roof edge detailing, fire could ignite the roof sheathing, and enter into the attic. If a vinyl gutter had been used instead of this metal gutter, it would have quickly detached from the fascia board and fallen to the ground, potentially igniting near-home vegetation (if present) or siding (if combustible).

This home used wire mesh screening to cover the gutter. As shown here, one potential disadvantage is the accumulation of debris, not in the gutter, but in back of the gutter cover device. If this debris is ignited by embers, it will provide a flaming exposure to the field of the roof (which a Class A roof should be able to handle). Still, this photograph should show that inspection and maintenance needs to be continued, even when gutter cover devices are used.

This is the through-roof vent on the asphalt composition shingle portion of the roof. The 1/4" mesh screen is clearly visible in the vent.

Wildland-Urban Interface Demonstration Building
Roofing & Gutters Vents Eaves & Soffits Windows Siding Near-home