Flying embers landing on exposed wood can set your house on fire

By John Scarborough

Because roofs are so vulnerable to ember ignition, you should understand where weak points might be found and check those areas very closely.

Most of our houses in Ashland use asphalt shingles. For new construction, they must be at least Class A, which means that — when new — they can be exposed to high heat for about two to four hours before the roof ignites. Don’t assume that a Class A roof installed 10 years ago is still “Class A” — shingles can degrade due to storms, moss and algae, even bird droppings. Inspecting the condition of shingles using binoculars can reveal upturned edges, tears, and slippage, all of which can make a roof susceptible to ember ignition. Gutter covers may reduce the need for maintenance, but they still need to be checked to see if they need cleaning, and whether they are holding together as expected.

If you have a metal roof, check what’s under the metal; metal can get so hot that wood sheathing can ignite.

Tile roofs can last 100 years. They can lower utility costs and are durable. But they are also brittle, and because of their weight, require a more robust roof structure. Some types are more vulnerable to ember ignition than others, because of gaps opened during settling. Look for damage from earthquakes and age. Open ends of the tiles should be closed with bird stops (also known as eave stops); if not, check to see if birds have nested there or debris accumulated, and remove what you can. If you need to walk on tile roofs for inspection, it’s best to get professional help.

In Ashland, roofs for newly constructed houses cannot use wooden shakes. Western red cedar, which was frequently used for shakes, has an ignition point of 375 degrees; considering that a cigarette burns at about 550, it just doesn’t make sense to use them.

Debris can accumulate on all roof types — in valleys, against skylight curbs, dormer sidewalls, front walls, etc. Check regularly throughout the year. You may be able to remove debris by sweeping or raking from a ladder on one-story structures, or by training a hose on it (but do not use a pressure washer, as that can damage shingles, even dislodge them). Hire a professional or learn professional methods of securing yourself when working on a roof.

While your home may be subjected to the flaming front of a wildfire for only 2 to 10 minutes, your roof, structures, and landscaped areas can collect wind-blown burning embers for hours after it’s passed; embers may also have started a smoldering fire that isn’t seen during a short walkthrough.

Complex roofs can complicate maintenance. Several horizontal-to-vertical intersections (e.g., on dormers) can make roofs more vulnerable to wildfire, especially wind-blown ember storms. On dormers, where the dormer roofline dies into the main roof gable (or “rake”), pockets can be formed where birds can build nests, or leaves and other debris can blow in, stick, and ignite. Wind currents can create ember paths that you might not have considered. Your principal concern is not just small embers but embers as big as a wooden shingle, for example, that can be firmly lodged against a flammable surface.

Gutters

Embers landing in gutter debris can start a fire that may open access to the attic. Spring is the best time to remove leaves and other debris from your gutters, though with the rise in midwinter wildfires, late fall is increasingly important. In both cases you reduce fire risk. While doing that, check on the gutters’ water flow, structural integrity, and any signs of water damage to the roof edge immediately above the gutters. Loosened gutter clips can block debris, which then blocks water from flowing to the downspout. The downspout itself can be blocked with debris; you may be able to flush it out with your garden hose, otherwise cleaning may require removing it to get at the plug.

The advantage of metal gutters is that in a fire, they’re likely to stay in place. Plastic gutters will melt, so that if they fall on or into dry grass, flammable plants, or other fuel, they will start fires.

If your roof has metal flashing (aka “drip edge”) at its edges, check to see that it overlaps the lip of the gutter. Otherwise water can come back up on the underside of the sheathing, or drop through to the fascia and develop rot. If your roof does not have metal flashing, the protection it provides makes installation worthwhile.

Next week: Decks and patios

John Scarborough is a member of the Fire Adapted Ashland Committee, where he works on the Wildfire Risk Assessment Program (WRAP), which at an Ashland resident’s request will perform a wildfire risk assessment of the resident’s property (click here to go to the request form). Email Scarborough at [email protected].

First Fire Safe Home Work column: What can you do to reduce your wildfire risk? (April 4)