WUI Structure Hardening & Defensible Space – Key Exam Notes

Project Overview

Goal: develop engineering-based WUI Virtual Handbook for fire departments to perform property fire-risk assessment & recommend mitigation
Led by SFPE & SFPE Foundation under DHS-FEMA FP&S grant (2020)
Audience: fire service & prevention professionals; handbook offers guidance – not sole method

Core Wildfire-Ignition Drivers

Embers (firebrands) cause ≥ $\tfrac{2}{3}$ of home ignitions
Direct flame impingement & radiant/convective heat amplify risk
Combustible roofs, vents, edges, joints & nearby fuels = critical vulnerabilities

Roof Systems – Key Actions

Install Class A roof assemblies (covering + underlayment + deck)
Remove debris; bird-stop tile openings; flash valleys/edges with metal
Under steep roofs: use $\ge 5/8$ -in Type X gypsum or Class A cap-sheet under metal/wood coverings
Low-slope roofs: ensure non-combustible insulation or gypsum board below covering

Roof Openings

Vents & Chimneys: screen with non-combustible $\le1/8''$ (prefer $1/16''$ ) mesh; use ASTM E2886-listed vents
Provide spark-arrestor caps ( $\le1/2''$ mesh) on all chimneys
Avoid plastic ridge/off-ridge vents; prefer baffled metal or dormer-style

Joints & Flashing (Roof & Wall)

Seal gaps with fire-rated caulk/ fire-stop; use metal flashing
Clean debris at valleys, roof-to-wall, skylights; protect skylight perimeters with metal

Roof Perimeter Features

Edge: add metal drip-edge; keep gutters clean; fit non-combustible guards
Gutters: favor metal; remove debris pre-fire season; relocate plastic away from structure

Attic/Crawlspace Venting

Enclose eaves (soffit) with ignition-resistant material; avoid open-rafters
Maintain horizontal soffits; protect vents as for roof

Wall Systems – Essentials

Prefer non-combustible / ignition-resistant cladding (stucco, fiber-cement, masonry, metal)
Maintain $\ge6''$ vertical non-combustible clearance from grade to siding
Upgrade vulnerable doors/windows: solid-core/metal doors; dual-pane (tempered outer) windows; install $\le1/8''$ metal screens
Flash & seal window/door joints; keep Zone 0 ( $0–5'$ ) fuel-free

Decks, Balconies & Fences

Use non-combustible/ignition-resistant decking & rails; enclose undersides or protect with $5/8''$ Type X gypsum
Keep $0–5'$ beneath & around decks free of fuels; relocate wood piles >30' or enclose
Break wooden fences $\ge5'$ from house with metal/non-combustible segment

Exterior Attachments & Sprinklers

Awnings/canopies: select metal or NFPA 701-rated fabric; clear debris
Exterior sprinkler systems lack standards; treat only as supplemental, not substitute for defensible-space & hardening

Defensible Space (Home-Ignition Zone)

Zone 0 ( $0–5'$ ): totally non-combustible—hardscape, rock mulch, no vegetation/wood piles
Zone 1 ( $5–30'$ ): “Lean, Clean, Green” – low, hydrated plants; trim branches >6' above ground & $10'$ between crowns; mow grass $\le4''$
Zone 2 ( $30–100'$ ): thin, prune to reduce ladder fuels; create fuel-breaks (drives, paths)
Increase spacing on slopes: shrubs $(2\times,4\times,6\times$ height for < $20\%$ , $20–40\%$ , > $40\%$ slope)

Vegetation Selection & Care

Fire-adapted traits: high moisture, low resin, deciduous, sparse litter
Avoid plants with waxy leaves, oily/resinous foliage, dense litter (e.g., juniper, Italian cypress, eucalyptus)
Irrigate appropriately; remove dead material; maintain clearance from structures/windows

Inspection & Maintenance Quick List

Annual (or more frequent) roof & gutter cleaning
Seasonal vent/soffit inspection & mesh integrity check
Trim trees, prune shrubs, mow grasses before fire season
Verify seals at joints, flashing, and around penetrations
Relocate combustibles (bins, furniture, BBQ, vehicles) outside Zone 0

Priority Retrofits (High-to-Low)

Create/maintain $0–5'$ ember-resistant zone
Replace combustible roof covering with full Class A assembly
Install ember-resistant vents ( $\le1/8''$ mesh)
Upgrade single-pane windows to dual-pane tempered
Enclose/equip decks with ignition-resistant materials