Defensible Space Guide: The 3 Home Ignition Zones

Defensible space isn’t one ring around your house — it’s three zones, each with different rules, because each zone stops fire in a different way. Understanding why the distances are what they are makes the work easier to prioritize when you’re short on time, money, or both.

This guide walks through each zone using the Home Ignition Zone (HIZ) framework used by the Colorado State Forest Service and Routt County’s local fire authorities. If you want the numbers on what this typically costs to have done, see the defensible space cost guide. If you’re trying to time this work around a grant cycle, see grants and rebates.

Zone 1: 0–5 feet — the Immediate Zone

This is the highest-leverage zone and the cheapest to do yourself. Research from wildfire behavior studies consistently shows that homes ignite most often from embers landing in or near combustible material right against the structure — not from a wall of flame reaching the house.

In this zone:

• Remove all dead vegetation, dry leaves, and pine needles from the ground, roof, and gutters.
• Move firewood stacks, propane tanks, and mulch beds out of this zone entirely — mulch especially is a common ignition point that gets overlooked.
• Keep any plants within 5 feet of the structure low, well-spaced, and irrigated (or replace with gravel/hardscape).
• Check under decks and porches — this space collects debris and is rarely visible from ground level.
• Trim tree branches that overhang the roof or touch exterior walls.

If you only do one thing this season, do this zone. It’s also the zone covered in our seasonal checklist.

Zone 2: 5–30 feet — the Intermediate Zone

This zone is about spacing, not clearing everything. The goal is to interrupt a fire’s ability to move from plant to plant to your house — “horizontal continuity” in wildfire terms.

In this zone:

• Space tree canopies so they’re not touching — a rule of thumb used locally is roughly 10 feet between crowns on level ground, more on slopes, since fire moves faster uphill.
• Remove “ladder fuels” — shrubs and small trees growing under larger trees that let ground fire climb into the canopy.
• Keep grass mowed to a low height through fire season.
• Prune tree branches up so the lowest limbs are well above surrounding shrubs.
• Space any remaining shrub islands well apart from each other and from Zone 1.

This is usually where tree removal and larger vegetation thinning enters the picture, which is also why it’s the zone most likely to require a contractor with the right equipment rather than DIY hand tools.

Zone 3: 30–100 feet — the Extended Zone

On a typical Routt County lot this zone often extends to or past your property line, especially on smaller in-town parcels — which is part of why “how much of my property counts” is a common source of confusion on the lead form. If your zone 3 overlaps a neighbor’s land or open space, mitigation coordination becomes a shared conversation, not just your own project.

In this zone the goal shifts from “clear it” to “thin and manage it”:

• Remove smaller conifers growing in clusters (dog-hair thickets) that can carry fire quickly.
• Reduce heavy accumulations of downed and dead wood.
• Continue the crown-spacing principle from Zone 2, though spacing requirements are typically looser this far out.
• On sloped terrain, extend mitigation further upslope from the house, since fire moving uphill accelerates.

Why the distances matter

The 5/30/100 boundaries aren’t arbitrary — they roughly track how embers, radiant heat, and direct flame contact behave at different distances during wildfire conditions. Zone 1 addresses ember ignition (the most common cause of home loss). Zone 2 and 3 address a fire’s ability to build momentum and throw embers or radiant heat far enough to matter at your house.

A note on local requirements

Some Routt County jurisdictions, HOAs, and the areas covered by local fire protection districts have their own defensible space ordinances or CWPP (Community Wildfire Protection Plan) guidance that can be stricter than the general HIZ framework above. Confirm specific requirements with your local fire district or the Routt County Wildfire Mitigation Council before treating this guide as a compliance checklist rather than general guidance.

Next steps

• Not sure how much of this you can do yourself vs. need to hire out? Start with the cost guide.
• Ready to get quotes? Head to Find a Pro — tell us about your property once and we’ll route you to the right kind of contractor for the job.