The Wildfire Exposure Rating system translates wildfire science into practical building specifications. Each level targets specific wildfire attack mechanisms: ember attack, radiant heat, and direct flame contact.
The Wildfire Exposure Rating (WER) draws from Natural Resources Canada (NRCan), National Institute of Standards and Technology (NIST) investigations, Insurance Institute for Business & Home Safety (IBHS) research, Australian Standard AS 3959, and Canadian building codes. Every specification is pass/fail — it meets the standard or it doesn't.
Once you know your WER level, the design guides tell you exactly what to do about it.
Each level is a complete set of measures matched to a specific exposure category. Your WER level is determined by your site conditions — vegetation distance, slope, and neighbouring structures. You implement the measures for your assessed level.
Ember Attack
Class A fire-rated roof. Gutter guards. 1.5m NC perimeter. Basic defensible space. Close Neighbour Exposure Level (CNEL) system applies if any structure (neighbours or own accessory buildings) within 10m.
Key measures
Class A roofing, metal gutter guards, 1.5m NC perimeter zone, basic vent screening (3mm mesh), removal of combustible debris, and Zone 1 vegetation management. CNEL applies if any structure within 10m (including own accessory buildings): CNEL-1 (6–10m) — clear gap, NC ground cover, NC fencing, enclosed soffits on facing elevation. CNEL-2 (4–6m) adds NC cladding on CNEL zone; wildfire shutters recommended as retrofit. CNEL-3 (2.4–4m) requires Type X sheathing, mineral wool, and wildfire shutters on all facing openings.
Ember + Radiant Heat
Enclosed NC soffits. Ember-resistant vents. Tempered glazing. NC or fire-rated fencing. CNEL measures on exposed wall portions within assessment distance.
Key measures
Enclosed NC soffits, ember-resistant vents (ASTM E2886), tempered/laminated glazing, NC or fire-rated fencing within 6m of structures. CNEL on exposed wall zones (per 45° splay method): CNEL-1 adds NC soffits and clear gap. CNEL-2 adds NC cladding; wildfire shutters recommended as retrofit. CNEL-3 adds Type X sheathing, mineral wool, and mandatory shutters. Fire-rated timber alternatives accepted for fencing and outbuildings.
Ember + Radiant Heat + Debris
NC cladding to ground level. Wildfire shutters on all openings. NC or FRT decking. CNEL measures on exposed wall portions within assessment distance.
Key measures
NC cladding to ground (or engineered equivalent), wildfire shutters, NC/FRT decking, fire-rated timber options for outbuilding framing. CNEL on exposed wall zones (per 45° splay method): CNEL-2 largely overlaps WER-3 specs; shutters recommended. CNEL-3 adds sealed soffits (no vents), radiant heat barrier, and mandatory shutters on all facing openings.
Direct Flame + Full Exposure
Complete NC exterior. BAL-40+ equivalent (Bushfire Attack Level, the Australian benchmark). No timber alternatives. P.Eng. assessment required. CNEL integrated into full envelope.
Key measures
Complete NC envelope (no timber alternatives), fire-rated wall assemblies, BAL-40+ equivalent (Bushfire Attack Level, the Australian benchmark), steel/bronze shutters all elevations, P.Eng. assessment with radiation modelling. CNEL fully integrated — WER-4 exceeds all three CNEL tiers. No additional CNEL measures required.
Fire-Rated Timber
The WER system does not require everything to be noncombustible. Where a specification says "NC or fire-rated," fire-rated timber is an acceptable alternative when it meets minimum section dimensions. Large-section timber chars at a predictable rate (approximately 0.65mm/min for softwood per Eurocode 5) and can maintain structural integrity for defined periods.
For fencing, outbuilding framing, and deck substructure, timber sized to resist ignition for the design fire exposure period is an acceptable alternative to noncombustible materials at WER-1 through WER-3. Minimum section dimensions are specified in each design guide and in Construction Detail Guide 5 (Fencing) and Guide 6 (Walls & Cladding). At WER-4, all exterior materials must be noncombustible — no timber alternatives.
Close Neighbour Exposure Level (CNEL)
Most Canadian subdivision homes are built 2.4–6 metres apart, wall to wall. This has contributed to community-wide devastation during major fire events. We believe this is a Canada-wide vulnerability that needs to be addressed. At these distances, a fully involved neighbouring structure produces enough radiant heat to ignite combustible materials on your home — regardless of your wildland exposure level. The CNEL system addresses structure-to-structure fire spread as a separate hazard from wildland exposure.
CNEL applies to any structure within the assessment distance — including detached garages, workshops, sheds, and carports on your own property. Three tiers based on wall-to-wall separation: CNEL-1 (moderate, 6–10m), CNEL-2 (high, 4–6m — the most common Canadian suburban scenario), and CNEL-3 (severe, 2.4–4m). Below 2.4m is outside CNEL scope — consult a P.Eng. Measures apply to the exposed wall zone per the 45° splay method.
Measuring the distance: Use the actual wall-to-wall separation as measured on site. For new construction, use the lesser of the actual distance or the minimum zoning setback (since a future neighbour could build to the setback line). For existing buildings where the separation is less than the current zoning setback (existing non-conforming), use the actual measured distance — this is the real exposure. CNEL measures apply to any part of the building envelope that falls within the horizontal exposure zone at that separation distance, determined by the 45° splay from the nearest point of the exposing structure.
The permit trigger: Any wall upgrade requires a building permit, which triggers NBC spatial separation compliance (9.10.15.5). This code-compliant assembly becomes the basis of design — then CNEL layers on WUI-specific measures: wildfire shutters, ember-resistant vents, sealed soffits, and NC ground cover. The 2.4m floor aligns with the NBC’s most-stringent residential threshold (1.2m limiting distance per side).
Wildfire shutters are often a good retrofit solution and common in places like Australia — they install over existing windows without replacement and provide an opaque radiant heat barrier that glass cannot. Recommended at CNEL-2, required at CNEL-3. The eave problem: eave-to-eave separation is often 1–2m less than wall separation. CNEL requires a separate eave-to-eave assessment — eaves under 2m apart need sealed NC soffits with no vents on the facing eave.
CNEL and WER are complementary — a home may have both a wildland WER level and one or more CNEL levels on different faces. Apply whichever is more stringent within the CNEL-rated zone. Download the full CNEL Guide →
Clear Gap + Ember Defence
Radiant heat at wall: 4–12 kW/m²
Separation: 6–10 m wall-to-wall
Typical triggers: Detached garage or neighbour's house 6–10 m away. NC ground cover in gap. Enclosed NC soffits on facing elevation. Ember-resistant vents on facing wall.
NC Cladding + Shutters Recommended
Radiant heat at wall: 12–40 kW/m²
Separation: 4–6 m wall-to-wall
Typical triggers: Most common Canadian suburban scenario. NC cladding on exposed wall zone. Type X gypsum sheathing. Metal rain screen furring. Wildfire shutters recommended. Tempered or laminated glazing on facing openings.
Full Hardened Assembly + Shutters Required
Radiant heat at wall: 40–80+ kW/m²
Separation: 2.4–4 m wall-to-wall
Typical triggers: Tight urban lots, zero-lot-line townhouses, row housing. All CNEL-2 measures plus wildfire shutters required on all facing openings. Mineral wool insulation in wall cavity. Sealed NC soffit, no vents on facing eave. Complete NC envelope on exposed face.
Standard construction details and specifications are currently under development. The design guides provide material specifications and general assembly requirements. Detailed construction drawings, product-specific installation guides, and the Component & Assembly Reference database are in active development. Take the survey to help us prioritize.
Verification Pathways
The WER system recognizes three pathways to meet each specification. This mirrors how building codes work — a prescriptive path for straightforward compliance, and alternative solution paths for flexibility.
1. Deemed-to-Satisfy
Materials and assemblies explicitly named in the FireHard specification. If the design guide lists it, it meets the standard. Example: fibre cement panel, metal cladding, stucco, or masonry all satisfy "noncombustible cladding" without further testing.
2. Tested Equivalent
Products tested to the referenced standard by a recognized testing laboratory. Example: an ember-resistant vent not listed in the guide but tested to ASTM E2886 by an accredited lab meets the WER-2 vent specification. The manufacturer's test report is the evidence.
3. Engineered Alternative
A P.Eng. assessment demonstrating equivalent performance through analysis. Example: a heavy-timber fence post (140×140mm minimum) may satisfy the WER-2 fencing specification through charring rate analysis, even though it is not noncombustible. The engineer's sealed report is the evidence.
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