Tecnobosque Wildfire Knowledge Graph · Built Environment
Reference Concept · v1.0Definition → relationship → calculation → evidence context
The Home Ignition Zone (HIZ) is the structure and its immediate surroundings considered as the primary system that determines whether a home is likely to ignite during a wildland-urban fire.
HIZ
What is home ignition zone?
The Home Ignition Zone concept treats structure ignition as a local exposure problem. The condition of the home, attached features and fuels close to it can determine whether a wildfire becomes a structure loss.
This does not mean the larger wildfire is unimportant. It means that incident-scale fire behaviour must ultimately be translated into the heat, flame and ember exposures that reach a specific building.
Why it matters
Research on WUI losses shows that structure characteristics, nearby combustibles and ember exposure can dominate ignition outcomes even when the main wildland flame front is farther away.
The HIZ moves the question from “How big is the wildfire?” to “What fire exposures actually reach this home, and what can ignite here?”
What controls or changes this quantity?
Windborne firebrands can enter openings or ignite receptive materials around the building.
Vegetation, fences, decks or neighbouring structures can create flame pathways to the home.
Nearby flames or burning structures can heat vulnerable components without direct contact.
Roof, vents, windows, decks and cladding influence whether external exposure becomes ignition.
Engineering context
Roof, vents, windows, decks, siding and attached components.
The first few feet where embers and small combustible pathways are especially important.
Vegetation arrangement and fuel continuity farther from the structure.
Adjacent structures and parcel-to-parcel spread can become dominant in dense WUI settings.
How to interpret it correctly
- Analyse the structure and surroundings together.
- Separate ember, flame-contact and radiant-heat pathways rather than using one generic “wildfire risk” label.
- Use local zone guidance for treatment distances, but retain the broader HIZ systems concept.
- Do not infer that a treated HIZ guarantees survival under every exposure.
Use the calculator as a transparent technical aid and keep its assumptions explicit.Explore Home Ignition Zone Geometry →
Why it matters in wildfire analysis
Post-fire investigations frequently find mixed exposure mechanisms: embers, local yard ignitions, attached combustible features and neighbouring structures. The HIZ provides a useful frame for organising those pathways.
Tecnobosque connects HIZ concepts to Zone 0, defensible space, radiant heat and retrofit planning rather than treating each as an isolated checklist item.
Limitations and boundaries
- HIZ is a conceptual framework, not a site-specific fire-behaviour simulation.
- Zone distances used by agencies are practical guidance and do not create a hard physical boundary for embers or radiation.
- Community-scale structure-to-structure spread can overwhelm property-only assumptions.
Home Ignition Zone FAQ
What is the Home Ignition Zone?
It is the home and its immediate surroundings considered together as the system where wildfire exposure can lead to structure ignition.
Is the HIZ the same as defensible space?
No. Defensible space is a treatment strategy around the home; the HIZ includes the building itself and its ignition vulnerabilities.
What can ignite a home in the HIZ?
Important pathways include embers, direct flame contact and radiant heat from vegetation, attached materials or nearby structures.
How large is the HIZ?
Different guidance documents use practical zone distances, often extending roughly 100 ft or more. The exact treatment framework is jurisdiction-specific.