The expanding reach of urban development, coupled with a changing climate, is fueling a dangerous convergence: wildfires escalating into urban conflagrations. Much of the discussion around wildfire resilience has focused on single-family homes in the wildland–urban interface (WUI). But as recent disasters show, commercial and multifamily buildings face their own unique, and often greater, risks.
The scale, shared surfaces, and mechanical complexity of these structures make them especially vulnerable to radiant heat, ember exposure, and smoke infiltration. The Eaton and Palisades fires of early 2025 destroyed nearly 1,000 multifamily and commercial buildings combined, underscoring the urgency of extending resilience strategies beyond single homes to larger building types.
Unique Vulnerabilities of Larger Buildings
- Large, flat roofs: These surfaces can accumulate combustible debris, collect wind-blown embers, and contain multiple points of vulnerability such as skylights, HVAC units, solar panels, and other penetrations.
- Rainscreen systems: While effective for moisture management, vented rainscreens can act as chimneys if unprotected, drawing flames and embers into wall cavities.
- Shared systems: Interconnected HVAC and mechanical systems provide potential entry pathways for embers and smoke.
- Mixed uses: Buildings that combine residential, commercial, and public functions increase the stakes for occupant safety and continuity of operations.
Even modern construction can fail under these conditions. The 2023 Lahaina Fire revealed how ember penetration undermined otherwise code-compliant structures. Yet two contrasting examples illustrate how design matters: one so-called "miracle house" with reinforced concrete walls, a heavy-gauge metal roof, and minimal landscaping survived while adjacent blocks burned. And in the same community, the Lahaina Roads apartments, a concrete multifamily complex on Front Street, remained structurally intact while wood-framed neighbors were reduced to ash, enabling eventual re-occupancy after mechanical and utility repairs. These cases demonstrate that noncombustible construction, defensible space, and careful detailing are decisive factors in survival.
Protecting Wall Assemblies
Rainscreen wall assemblies are particularly at risk. If not carefully detailed, cavities can draw embers upward like flues. Strategies include:
- Non-combustible insect screens: Metal mesh (≤1/8 inch openings) at top and bottom of cavities, per California Building Code Ch. 7A and IBHS guidelines.
- Cavity fire blocking: Horizontal mineral wool barriers at intervals to stop vertical flame spread.
- Non-combustible insulation: Insulation materials such as mineral wool resists ignition and maintains performance at high heat, unlike foam-based products.
- Cladding and gaps: Specify fiber cement or metal panels and minimize air gaps to limit convective heat.
- Base and head detailing: Use flashing or intumescent materials to seal entry points and protect transitions.
Windows, Doors, and Openings
Openings remain one of the weakest points in fire resilience. Key measures include:
- Tempered glazing: Dual-pane assemblies with at least one tempered pane withstand radiant heat far longer.
- Non-combustible frames: Aluminum, steel, or ignition-resistant wood prevent openings from being compromised.
- Fire-rated doors: Exterior doors, especially at balconies and decks, should be rated or constructed of non-combustible materials.
- Screens: Windows and vents screened with ≤1/8 inch metal mesh to block embers.
- Perimeter sealing: Tight fire-rated seals around frames with intumescent caulk or backer rod.
These measures, common in WUI overlays and codes like IWUIC and NFPA 1140, must be applied consistently in commercial and multifamily projects where occupant loads are higher and escape routes more complex.
Roofing and Rooftop Equipment
Large commercial and multifamily roofs present critical wildfire challenges. Mitigation includes:
- Class A fire-rated roofing materials and assemblies.
- Regular maintenance to clear combustible debris from drains, gutters, and behind equipment.
- Non-combustible curbs and flashing around penetrations.
- Protected equipment: Enclose rooftop HVAC or electrical systems in non-combustible housings.
- Defensible perimeters: Maintain setbacks free of fuel loads at parapets and edges.
Connected fuels such as wooden fences, decks, or outbuildings adjacent to multifamily complexes or commercial sites have been shown to accelerate spread in events like Lahaina. Replacing these with noncombustible alternatives, masonry walls, gravel mulch, metal enclosures, interrupts fire pathways and reduces structure-to-structure ignition risk.
Smoke Resilience: Beyond the Flames
Even when flames never reach a building, wildfire smoke is a building emergency. In 2023's widespread smoke episodes, asthma emergency-department visits rose 17% above normal on smoke days across the U.S. Longer-term exposure to wildfire-origin PM₂.₅ is associated with higher mortality, adverse birth outcomes, and worsened respiratory illness in children. Research also indicates wildfire smoke may be more harmful than other pollution sources because it often contains volatile organic compounds and heavy metals in addition to fine particulate matter.
For larger facilities, smoke impacts can be devastating. During the 2021 Marshall Fire in Colorado, Avista Adventist Hospital, though spared from flames, had to evacuate due to smoke infiltration that contaminated air-handling systems and interior spaces. The hospital only reopened after months of remediation.
To protect commercial and multifamily occupants, architects should:
- Design HVAC systems with a dedicated "wildfire smoke mode" per ASHRAE Guideline 44-2024.
- Specify MERV-13 or HEPA filtration with sealed ductwork and shafts.
- Provide outside-air shutoff or enhanced filtration capability and positive pressurization in refuge areas.
- Incorporate airtight detailing at penetrations and assemblies to reduce infiltration.
The Forgotten Hazard: Flooding After Fire
Wildfire damage doesn't end when flames are extinguished. Burn scars often create hydrophobic soils that shed rain rather than absorb it, greatly increasing flood and debris flow risk. Even modest precipitation can produce devastating secondary hazards.
Following the January 2025 Palisades Fire, heavy rains triggered debris flows that damaged or destroyed homes untouched by flames. In hillside neighborhoods like Castellammare, debris inundated foundations and compromised structural stability.
For commercial and multifamily buildings, post-fire flooding can:
- Inundate parking garages and basements.
- Short out electrical and mechanical systems.
- Block stormwater systems with sediment and debris.
- Erode structural foundations.
Protective strategies include raising vital systems above potential flood levels, using water-resistant materials, designing graded landscapes or berms, and providing redundant drainage paths.
Codes, Standards, and the Role of Advocacy
Resilient design draws from multiple guidance sources:
- California Building Code Ch. 7A and FEMA P-737 provide construction methods for wildfire zones.
- IWUIC and NFPA 1140 establish fire-resistant construction standards for WUI projects.
- Local amendments and enforcement are often inconsistent, requiring strong advocacy from architects to ensure adoption and compliance.
Ultimately, codes define minimums. Architects committed to resilience should see them as a baseline, not a finish line.
Holistic Resilience Planning
Wildfire resilience cannot be isolated from broader hazard planning. Effective strategies combine fire-resistant design with post-disaster recovery measures, especially in flood-prone burn scars. Priorities include:
- Conducting multi-hazard risk assessments that integrate fire and post-fire flooding.
- Applying both fire and flood standards consistently across design decisions.
- Educating clients, owners, and occupants on hazard mitigation strategies.
- Fostering collaboration among architects, engineers, code officials, and community leaders.
As Lahaina and Marshall showed, survival in one phase of disaster does not guarantee safety in the next. Truly resilient buildings are those designed with the full disaster cycle in mind.
Designing to Survive and Recover
Wildfires are becoming more destructive, more frequent, and more urban. Commercial and multifamily buildings, where lives, livelihoods, and communities intersect, require enhanced protection measures.
Through fire-resistant construction, ember-resistant detailing, smoke- and flood-mitigation strategies, and strong advocacy for code adoption, architects can ensure their projects not only survive but recover more quickly.
Resilience is not a single measure, but an integrated design philosophy. As architects, our work must anticipate the full spectrum of wildfire hazards to create built environments that stand firm, protect people, and foster community recovery.
Jacob Kwiatkowski is a fire and emergency management professional with over 20 years of experience in firefighting, building code enforcement, and community resilience planning, currently serving as an Emergency Management Specialist with FEMA. Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect and consultant with over 36 years of experience in sustainable building design. He is Director of Sustainability with Intertek Building Science Solutions.
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Alan Scott FAIA
Intertek, Building Science Solutions
Portland OR
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