Fire Hardening and Passive House - A Concise Overview

The synergies:

• Airtight envelope = ember-tight envelope. Most fire losses come from ember intrusion, not flame contact. The passive house minimum performance standard of ≤0.6 ACH50 envelope with no attic or crawlspace vents (unvented, conditioned assemblies) removes the single most common ignition pathway. Where vents are unavoidable, use ember-rated/intumescent vents or 1/8" corrosion-resistant mesh.
• Mineral wool as continuous exterior insulation. It hits both targets: thermal-bridge-free CI and a noncombustible layer that protects sheathing. This is the place to deviate from the EPS/polyiso common in passive house builds — rigid foam behind cladding is a real liability in ember storms.
• Triple glazing. Already standard for passive house, and glass failure is a primary ignition route — multiple tempered panes buy significant radiant-heat and breakage resistance. Spec tempered at minimum on exposed elevations; consider fire-rated units facing fuel loads.
• Simple form factor. The compact massing passive house wants for surface-to-volume ratio also eliminates the roof-wall intersections, dormers, and inside corners where embers accumulate. Boxed/minimal eaves serve both goals.
• Mechanical ventilation instead of operable-window reliance. An HRV/ERV lets the house stay sealed during smoke events. Add motorized dampers with a smoke-detection or manual shutoff mode, ember screening on intake/exhaust hoods, and MERV 13+ (ideally with carbon) filtration — a genuine value in smoke-season country.

Fire-hardening items passive house doesn't cover:

• Class A roof assembly — metal or concrete tile over cap sheet — with metal drip edge and bird-stopped ridge/eave details.
• Noncombustible cladding (fiber cement, stucco, metal) — and mind the rainscreen: an open cavity can act as a chimney, so detail fire blocking or intumescent strips at openings and floor lines.
• Zone 0 discipline: nothing combustible within 5 ft of the structure — hardscape, gravel, no attached wood fencing (a fence is a fuse). Then managed zones out to 30 and 100 ft.
• Decks and appendages: noncombustible or ignition-resistant decking, sealed or screened under-deck areas — the most common flame path to the wall.
• Residential sprinklers, 6" noncombustible base of wall, and site basics: access width, water supply, address visibility.

For frameworks: California's Chapter 7A and the IWUIC are the code baselines, and the IBHS Wildfire Prepared Home standard is a good prescriptive checklist — it maps almost one-to-one onto the details above.

One honest tension to design around: passive house's preference for large south glazing conflicts with radiant exposure if the fuel load is on that aspect. Orientation studies should consider fire exposure the way you would look at solar gain.