Decks, Porches, and Balconies: Ignition-Resistant Materials and Under-Deck Protection
Decks ignite from above and below. The under-deck zone and deck-to-wall flashing are two of the highest-impact, lowest-cost retrofits available.
Per the 2026 SDC WUI Code §504.7.3.2, deck walking surfaces must comply with one of five performance-tested options for under-deck flame and ember exposure. The CAL FIRE-recommended 6″ metal flashing at deck-to-wall intersections closes the most common deck-fire-to-house-fire pathway.
Same-day and next-day appointments available.
Decks Burn from Above and Below — and Carry Fire to Your Home
Embers land on deck surfaces and ignite from above. Flames from burning vegetation catch stored combustibles under decks and ignite from below. The deck-to-wall junction is where fire most commonly travels from the yard to the structure itself.
Per the 2026 SDC WUI Code §504.7.3.2, deck walking surfaces must comply with one of five tested options. The CAL FIRE-recommended 6″ metal flashing at deck-to-wall intersections per §504.7.1 closes the most common pathway from deck fire to house fire.
- Decks ignite from embers landing on surfaces and from flames under stored combustibles
- The deck-to-wall intersection is the most common pathway for deck fire to reach the structure
- 6″ metal flashing at the deck-to-wall joint is a CAL FIRE recommendation and a same-week fix
- Clearing combustibles under decks is on the CAL FIRE Low-Cost Retrofit List
“The deck-to-wall intersection is where deck fires become house fires.”Six inches of metal flashing at that joint — one of the most cost-effective retrofits on this entire list.
Quick Wins, Smart Retrofits, and Full Upgrades
Combustible Removal and Clearing
Same-day fuel removal from under and around decks. On the CAL FIRE Low-Cost Retrofit List.
- Removing combustibles stored under and around decks
- Clearing debris between deck boards and at deck-to-wall intersections
- Removing combustible items from on top of the deck (mats, furniture covers, planters within 5 feet)
- Replacing wood lattice skirting with noncombustible alternatives (metal lath, fiber cement panels)
Flashing, Under-Deck Zone, and Partial Replacement
- 6″ metal flashing at deck-to-wall intersections per §504.7.1 (CAL FIRE recommendation)
- Under-deck ember-resistant zone — gravel, pavers, or concrete extending 5 feet beyond deck footprint
- Replacing damaged or rotted deck boards with noncombustible or ignition-resistant equivalents
- Partial deck replacement: first 1 foot of walking surface in noncombustible material (high-leverage partial fix)
- Deck and porch refinishing with OSFM-listed fire-retardant coatings
Full Deck Rebuild
- Full deck replacement with noncombustible materials (steel framing and concrete, stone, or metal decking surface)
- Full deck replacement with ignition-resistant materials meeting one of the five compliant options under §504.7.3.2
- Deck replacement coordinated with siding and exterior wall hardening
- Sloped or overhanging deck redesign for downslope ember exposure
Deck Work Often Connects to Siding, Fencing, and Zone 0.
A Structure Hardening Assessment evaluates your deck as part of the full ignition pathway picture — so you’re not fixing one thing while missing what’s connected to it.
What the Rules Actually Say
- 2026 SDC WUI Code §504.7 — Projections (decks and overhangs)
- 2026 SDC WUI Code §504.7.1 — 6″ vertical noncombustible covering at base of posts and walls
- 2026 SDC WUI Code §504.7.3.2 — Decking surfaces (five compliant material options)
- SFM Standard 12-7A-4 / 12-7A-4A — Decking flame exposure tests
- ASTM E2632 — Under-deck flame and heat exposure
- CDI Safer from Wildfires — Cleared vegetation and combustibles under decks is a recognized discount measure
“Five compliant decking options — full replacement isn’t always required.”OSFM-listed composites and fire-retardant-treated wood both qualify under §504.7.3.2. A full concrete rebuild isn’t the only path.
Deck Retrofits Are Eligible for Grant Funding
CAL FIRE Low-Cost Retrofit List
Deck-to-wall flashing, under-deck clearance, and combustible removal are all on the CAL FIRE Low-Cost Retrofit List — eligible for multiple grant programs.
California Wildfire Mitigation Program
Deck flashing and under-deck zone work qualifies under CWMP for eligible San Diego County properties.
CDI Safer from Wildfires Discount
Cleared vegetation and combustibles under decks is a recognized measure for the CDI insurance discount framework.
Related Services and Pages
Cal Wildfire Defense provides non-regulatory wildfire risk assessments and mitigation support. We do not perform official CAL FIRE inspections or issue regulatory approvals.
Get a Structure Hardening Assessment.
A Structure Hardening Assessment evaluates your deck as part of all six ignition pathways — giving you documentation for contractor briefing, insurance conversations, and grant applications.