The three zones around your home

Think of your yard as three rings around the house. Each one does a different job. Together they keep a wildfire from walking up to your home, and give firefighters a safer place to work.

The three zones, seen from above. Measure from the walls of the house and from the edge of any deck.

Zone 1: the first 5 feet

Its job: nothing right next to the house can catch fire, so an ember that lands here goes out.

Use gravel, river rock, pavers or concrete next to the house. Remove bark mulch. Fire spreads through wood mulch but stops at rock.
Remove plants that burn easily, like juniper, from against the walls. Embers can light plants by the wall, and they can light the house.
Clear dry leaves and needles from the ground, the roof and the gutters. Embers can light leaves in gutters and set the roof on fire.
Clear out under decks and porches. Embers that land under a clear deck have nothing to burn.
Make any fence or gate within 5 feet of the house metal or another material that won't burn. A wood fence can carry fire straight to your house.
Keep firewood, lumber, trash cans and other things that burn out of this zone. Anything burning next to the house can set the house on fire.

Zone 2: 5 to 30 feet

Its job: slow a fire down and keep it low and small, so it can't build up heat next to the house.

Keep grass mowed short, under 4 inches, and watered if you can. Tall grass can carry fire up into bushes and trees.
Plant in small islands with gaps between them, instead of one long bed, so fire can't spread from plant to plant.
Space trees so their tops are at least 10 feet apart. Fire can jump from one treetop to the next.
Trim tree branches up 6 feet or more from the ground.
Remove brush growing under trees. It acts like a ladder that lets a ground fire climb into the treetops (see ladder fuels, below).
Keep at least 10 feet clear around a propane tank.

Ladder fuels: how a ground fire gets into the trees

A fire in short grass stays small and low. Firefighters can often stop it, and it gives off far less heat. The danger starts when it finds a way up. Ladder fuels are anything that lets a fire climb, step by step, from the ground into the trees: tall dry grass, then bushes, then low branches, then the top of the tree.

Left: grass, bushes and low branches make a ladder into the tree. Right: the same tree with the ladder taken away.

Tall, dry grass catches embers and carries the fire along the ground.
Bushes and young trees under bigger trees lift the flames higher.
Low branches reach down to the burning bushes and carry the fire up.
The treetop catches fire. A burning treetop is much hotter, throws far more embers and is very hard to put out, and near a home it can set the roof and walls on fire.

Break the ladder: trim the lower branches of trees 6 feet or more up from the ground, remove the bushes and young trees growing under bigger trees, and keep grass mowed short. Near the house, this matters most of all: a tree that can't catch fire from the ground can't hand the fire to your roof.

Zone 3: 30 to 100 feet

Its job: take away the fire's strength before it gets close, and keep it on the ground instead of in the trees.

Thin trees and brush so they are not touching each other. Fire can move from shrub to shrub and tree to tree.
Remove dead trees, dead branches and heavy piles of fallen limbs. Dead leaves, twigs and branches catch fire easily.
Cut dry grass and weeds down.
Stack firewood here, at least 30 feet from the house, not in Zones 1 or 2. Washington DNR advises 100 feet for homes in the forest.

On a slope, go farther. Fire climbs hills fast. Oregon State University Extension says the area to care for around a home reaches 100 feet, or 200 feet on steeper slopes. See why fire runs uphill.

A note on names

Different agencies number the zones differently. Oregon calls them the Immediate Zone (0 to 5 feet), the Intermediate Zone (5 to 30 feet) and the Extended Zone (30 to 100 feet). California calls the first 5 feet "Zone 0." The distances, and what to do in them, are the same. Your county or city may also have its own rules; check with your fire department.

Sources

Why each step matters: IBHS Wildfire Prepared Home, Ready.gov (FEMA).
Zone names and distances, gravel or pavers in the first 5 feet, removing bark mulch and junipers, clearing under decks, metal gates within 5 feet, grass under 4 inches, tree tops 10 feet apart, branches trimmed up 6 feet, removing ladder fuels (brush under trees), 10 feet around propane tanks, removing dead wood: Oregon State Fire Marshal, Oregon Defensible Space.
Small islands of plants, and 100 feet, or 200 feet on steeper slopes: Oregon State University Extension, Extending your protection.
Firewood at least 30 feet from the house: Minnesota DNR Firewise guide (PDF); 100 feet for homes in the forest: Washington DNR (PDF).
Washington's version, which uses larger distances for homes in the forest (firewood 100 feet away, 15 feet between tree tops, limbs removed 15 feet up): Washington DNR, 12 steps to defend your home from wildfire (PDF) and Washington DNR, defensible space.