Fireproofing Detached Structures: Sheds, ADUs, and Garages

When we talk about defending our homes from wildfire, we often focus on the main house—but detached structures like sheds, garages, and ADUs can be just as critical. These secondary buildings can become ignition sources during a wildfire and may even spread fire to your primary home if they’re not protected.

For California homeowners—especially in high-risk fire zones like Orinda, Lafayette, Moraga, and the Oakland Hills—fireproofing these outbuildings should be part of your wildfire defense strategy.

Why Detached Structures Are at Risk

Detached structures often:

• Sit closer to vegetation or property lines

• Are built with less fire-resistant materials

• Lack proper ventilation or ember protection

• Contain flammable contents (tools, gasoline, propane, etc.)

In high heat and wind, these smaller buildings can catch fire quickly and spread flames toward your main home, especially if they're within 30 feet.

The University of California’s Fire Network and Fire Safe Marin both recommend treating detached structures with the same level of fire-hardening as your house.

What Counts as a “Detached Structure”?

Here’s a quick list of structures to consider fireproofing:

• Accessory Dwelling Units (ADUs)

• Garages and workshops

• Sheds (metal or wood)

• Pool houses and cabanas

• Barns and small storage buildings

• Detached offices or studios

If it’s a building you care about—or one that sits near your home—it needs attention.

Step 1: Clean and Clear Zone Zero

Just like your home, the first five feet around detached buildings matter most. Remove:

• Firewood, mulch, and debris

• Plastic planters and storage bins

• Gasoline, propane, or lawn equipment

• Any flammable clutter under decks or overhangs

Replace combustible ground cover with gravel, decomposed granite, or pavers. This alone can significantly reduce the risk of ignition from embers.

Step 2: Upgrade Siding and Roofing Materials

Many sheds and garages are built with budget materials like T1-11 plywood or vinyl siding. These can ignite easily when exposed to embers or radiant heat.

Instead, use:

• Fiber cement siding or three-coat stucco for siding upgrades

• Metal or Class A-rated composition roofing

• Boxed-in eaves with ember-resistant soffit vents

• Metal trim around windows and doors to reduce heat transfer

Pro tip: Don’t forget the roof. Roofs with accumulated debris are a top cause of ignition.

Step 3: Protect Vents, Doors, and Windows

Detached structures still need airflow—but standard vents are vulnerable. Install:

• Ember-resistant vents (1/8” screening or intumescent designs)

• Dual-pane tempered glass windows (or no windows at all)

• Solid-core or metal doors with tight-fitting seals

Weatherstripping and door sweeps are especially important for ADUs that serve as living spaces.

Step 4: Remove or Relocate Combustible Items

Detached buildings often house the very items that make fires worse:

• Lawn mowers, weed whackers, and power tools with fuel

• Paint, aerosols, or cleaning chemicals

• Propane tanks or spare gas cans

Either:

• Move these items to a fire-rated storage locker

• Store them in metal cabinets with fire-rated doors

• Keep combustibles at least 30 feet from other structures, where possible

Step 5: Fireproof ADUs Like the Main Home

ADUs are often overlooked—but they’re growing in popularity across California. If your ADU is within 30 feet of your home, you should:

• Use noncombustible siding and roofing

• Box and seal eaves

• Install metal or fiberglass doors

• Use tempered glass for all windows and skylights

• Replace vinyl trim and gutters with metal

Berkeley’s Fire Prevention Inspection Guide treats ADUs as extensions of the primary structure for fire hardening.

Step 6: Full-Structure Fire Shielding for Detached Units

Some structures are too close, too old, or too hard to retrofit. That’s where passive fire shielding comes in.

Fire-resistant blanket systems can:

• Fully cover a shed, ADU, or garage

• Shield siding, roof, vents, and windows from embers and radiant heat

• Be deployed in less than an hour by trained crews

• Protect up to 3,000°F without water, power, or supervision

For homeowners with classic backyard studios or converted garages that can’t be rebuilt, this can be a game-changer.

What Fire Inspectors Are Looking For

Fire agencies across Contra Costa and Alameda County will assess:

• The distance between your home and detached structures

• The condition of the exterior (peeling paint, cracked siding, exposed vents)

• The contents inside (fuel, paint, chemicals)

• The ground cover around the structure

During fire season, inspectors may recommend or require removal of vegetation and relocation of flammable storage.

Extra Tips for Backyard Buildings

• Install metal mesh around decks or crawlspaces to keep embers out

• Use metal storage sheds over plastic or wood

• Anchor small sheds properly, so they don’t shift during high winds or earthquake retrofitting

• Label hazardous materials clearly for fire crews

• Use external lighting rated for heat exposure

Final Word

Detached structures deserve the same level of care and planning as your main home. Whether it’s your garage, garden shed, or a new ADU rental, protecting it with defensible space and smart building materials can stop a small spark from becoming a total loss.

And when you can’t afford to retrofit—or just want a backup plan—fire tenting and blanket shielding can offer the peace of mind your property deserves.

The Zone Zero Fire Shield team hopes you find this information helpful.

See also: [Understanding Zone 0] [Creating a Fire-Safe Perimeter] [Best Fire-Resistant Building Materials for Zone 0 and Zone 1]