Roof Risks: Design

Watch a video of wildfire testing at the IBHS Research Center to see how a house really performs during an ember storm. Then, answer the questions below to find out how vulnerable your home may be.

Does the roof design add to its vulnerability?

  • Does the roof have dormers or other features, such as those in a split level home, where vertical walls intersects with the roof, or the roof of one level overhangs the roof of a lower level?

The leaf litter shown in this photography has accumulated on the roof, adjacent to the wood shingle siding. This leaf litter can be easily ignited by wind-blown embers. The resulting flames will likely ignite the wood shingles, making the siding the vulnerable component of this roof.

If any of the above features are present, the roof is more vulnerable if:

  • Debris such as pine needles accumulate on the roof at the vertical wall-to-roof intersections.

  • If the exterior siding is combustible (wood and vinyl are common types of combustible siding).

  • Gutters are filled with debris.

  • Openings exist between the roof covering and roof deck at the edge and ridge. 

These are areas where fine fuels can accumulate and where embers can either accumulate or enter and lodge underneath the roof covering. If ignited by wind-blown embers, these fine fuels can potentially ignite the siding or fascia and/or roof sheathing, putting the entire structure at risk.

Reducing roof vulnerability

Limit the amount of debris that accumulates at the intersections between vertical walls, roof and in gutters.:

  • Regularly removing vegetative debris from the roof.

  • Replace combustible siding with noncombustible (such as a fiber cement product) or ignition-resistant material (such as exterior rated, fire-retardant treated wood).

  • Add metal flashing at the base of the wall to provide protection to the combustible siding. To avoid moisture-related durability problems with wood-based siding, make sure the metal flashing is tucked behind the siding at a lap joint.

  • Regularly clean and remove debris from gutters.

    • Consider gutter covers, which can minimize the accumulation of debris in gutters. Some gutter covers (for example, those that have a rounded design) can result in the accumulation of debris on the roof side of the cover, so maintenance may still be required.

    • If a cover is used, flat covers that are parallel to the slope of the roof covering should minimize the accumulation of debris behind the cover.

    • IBHS recommends the use of an integrated gutter (a combination of gutter and roof edge flashing) will help protect the fascia and roof sheathing, but if your home already has gutters, angle flashing can be installed at the roof edge.

  • Block gaps between the tiles and roof deck on barrel tile roof coverings and other roof types.

    • Use either manufacturer supplied materials or with a mortar or cement mixture. Openings will also occur at the ridge and roof-hips – these openings must also be filled. The manufacturer supplied devices are only for the roof edge (at the eave) and not for the ridge / hip. Both manufacturer supplied devices and mortar mix will reduce birds nesting in the area between the roof covering and the roof deck. Periodic inspection and maintenance will be necessary to make sure the devices and mortar mix are still in place.

    • Some metal roofs will also have small gaps at the roof edge. These should also be filled. Steel wool could be used for this application – select a more corrosion resistant product such as that made with stainless steel or a coated product.

    • IBHS recommends the use of end-stopping products that minimize the accumulation of debris in the space between the roof deck and covering and the entry of embers during wildfires.

Note that one of the manufacturer supplied “bird stops” is missing and should be replaced. In addition, note that these bird stops do not completely fill the space between the roof covering and roof deck – wind-blown debris and embers will still be able to get under the roof covering.

Note that one of the manufacturer supplied “bird stops” is missing and should be replaced. In addition, note that these bird stops do not completely fill the space between the roof covering and roof deck – wind-blown debris and embers will still be able to get under the roof covering.

 

Gaps can also occur with some standing seam metal roof coverings. These openings should also be filled.

Gaps can also occur with some standing seam metal roof coverings. These openings should also be filled.