As wildfires rage in the West, scorching millions of acres and burning homes and businesses, researchers are investigating what more can be done to better protect homes against blazes.

Researchers at the Insurance Institute for Business & Home Safety first determined what causes homes to ignite during a wildfire. They found that about 90% of homes and buildings were ignited by embers, not the actual wildfires. Embers can disperse for miles from their source and start a new fire when they land. Embers can enter a home through vents or dead landscaping, dry wood, or common homebuilding materials, BUILDER reports.

Some items around a home may pose a higher risk from these flying embers, particularly bark mulch, researchers note. “Wood mulch is a pretty common landscaping material, and I understand the use of it, but the problem is it’s combustible,” Daniel Gorham, research engineer at IBHS, told BUILDER. “It has lots of little crevices for those fire embers to land in, sit there, and smolder.”

A better ground cover would be gravel, which was shown to prevent embers from igniting a flame during an IBHS experiment.

Fire-resistant building materials can help provide better protection against wildfires, too, IBHS researchers found. They suggested creating zones of protection, such as the five-foot space around the perimeter of the home’s exterior walls, making sure it is clear of combustible materials, including dead leaves, twigs, bushes, or plants. Materials like gravel, brick, and concrete should be used instead.

IBHS researchers also urged builders to consider their product choices to better protect against wildfires, such as with the use of Class A fire rating for roofing, siding, window, and door products. They also recommended the use of multipane windows with tempered glass, providing a six-inch ground-to-siding clearance, and using 1/8-inch mesh to cover vents. Also, fiber cement board siding is shown to provide greater protection than wood shingles, the IBHS study shows.