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.
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.
© 2012 Insurance Institute for Business & Home Safety