Sheds, Shops and Outbuildings in a Wildfire

Why do sheds and outbuildings matter in a wildfire?

Because a burning shed is a large, sustained fire close to the house. Research summarized by NFPA says embers and small flames are the main way most homes ignite in wildfires, and a shed full of stored goods with a wood floor and open eaves is an easy ember target. Once it is burning it exposes everything nearby to radiant heat and flame for far longer than a passing grass fire would. The Colorado State Forest Service's Home Ignition Zone guide notes that radiant heat can ignite a home whether the source is a crown fire or an adjacent structure that has caught fire.

That is why wildfire guidance treats outbuildings near a home almost as parts of it. The IBHS Wildfire Prepared Home checklist applies its structure requirements to anything larger than 15 square feet within 30 feet of the home, listing garages, sheds, gazebos, playsets, greenhouses, pergolas, carports and accessory dwelling units.

How far should a shed be from the house?

The IBHS checklist, available to Montana homeowners since April 2026, says to locate detached structures at least 10 feet from the home and from other structures within 30 feet, and to limit the number of detached structures within 30 feet to three. Its higher Plus level goes further and asks that all detached structures be removed or relocated to at least 30 feet from the home.

For a new shed, 30 feet or more is the easy choice: it takes the building out of the zone that matters most. For an existing one, moving it may or may not be practical; small prefabricated sheds can often be relocated, while a shop on a slab cannot. Where a building cannot move, the clearance and hardening around it carry more weight. Placement uphill or downhill also matters, for the reasons explained in our slope and wind guide.

What clearance does each outbuilding need?

Its own noncombustible zone. The IBHS checklist says each structure within 30 feet must have its own 5-foot noncombustible zone, that for elevated structures such as sheds on skids or playsets the zone extends beneath them, and that the zones of different structures should not overlap. NFPA's guidance for the outer zone, 30 to 100 feet and beyond, says to remove vegetation adjacent to storage sheds and other outbuildings, and Missoula County's Home Upgrade Hub gives Missoula homeowners the same instruction.

So the treatment around a shed is a smaller version of the treatment around the house: gravel or bare ground in a band around it, no woodpile or lumber against its walls, no shrubs or tall grass touching it, tree limbs pruned back from the roof, and the space underneath cleared and closed off if it sits on blocks. Our first five feet guide covers what goes in that band.

What does IBHS ask of the building itself?

For solid-covered structures within 30 feet, the checklist requires a Class A fire-rated roof (asphalt, tile, slate or metal) and does not accept wood roofs, plastic corrugated panels or fabric shades. It asks for at least 6 inches of noncombustible material at the base of walls, posts and stairs. Open structures such as carports should be kept free of combustible items, and if their interior walls are exposed combustible material such as wood, the checklist says the structure must be enclosed. Wood pergolas are limited to 15 percent roof slat coverage.

Many older sheds and lean-tos on Montana properties fail on the roof, with wood shingles or plastic panels, or on the base, with wood siding sitting in the dirt. Roofing and siding are work for a building contractor; we do not do them. The clearing, gravel and tree work around the building are ours.

What should not be stored in a shed?

Propane cylinders, first of all. The Propane Education & Research Council's wildfire tip sheet says never to store, place or use a propane cylinder indoors or in an enclosed area, and names sheds and garages specifically. MSU Extension's WUI landscaping MontGuide says stored gasoline and diesel should be kept in fireproof storage away from the home and visibly labeled hazardous or flammable. A small fuel locker or a metal cabinet in a shed well away from the house is a reasonable arrangement; jerry cans on a wooden shelf in a shed against the garage are not.

Firewood is the one thing IBHS allows in an outbuilding: its checklist permits firewood in an approved accessory structure as an exception to the 30-foot woodpile rule, provided the structure meets the requirements above. Our firewood guide covers the rest. Hay is a different matter, covered in our guide to barns, hay and livestock.

What about the area under a shed?

Sheds on skids or blocks have a gap underneath that collects needles, leaves and nests, exactly like a low deck. The IBHS checklist groups elevated decks and sheds within 30 feet together: no storage underneath, at least 6 inches of noncombustible material at the base of posts and supports, and for structures 4 feet high or less, the perimeter enclosed with 1/8-inch corrosion-resistant metal mesh. Our under-deck guide goes into the details, and they apply to a shed in the same way.

What about water tanks and other large items?

The IBHS checklist covers several large items that are common on Montana properties. Combustible water storage tanks, such as plastic cisterns and rain tanks, should be at least 5 feet from the home and other large combustible items, not under overhead structures, with a 5-foot noncombustible zone beneath and around them. Hot tubs should be at least 10 feet from the home. Propane and fuel tanks have their own rules, covered in our propane tank guide. If the tank is meant to hold water for firefighting, our guide to ponds, cisterns and water supply covers that use.

Vehicles and equipment are the other large items. IBHS says not to park or store cars, ATVs, boats, RVs or similar equipment within 5 feet of the home, and a shop or carport full of fuel-filled machines is one more reason to keep those buildings well away from the house.

Do greenhouses, coops and playsets count?

Within 30 feet of the house, IBHS counts them all as structures. A plastic hoop greenhouse, a wood chicken coop with straw bedding and a wood playset with a bark mulch base are all combustible, and the bark under a playset is the same mulch hazard covered in our mulch and wildfire guide. The simplest answer is placement: put them beyond 30 feet where possible, with mowed grass or gravel around them, and keep the bedding and feed stored away from the house.

How do outbuildings fit into the rest of the plan?

They extend it. The 5 to 30 foot zone around the house, the 5-foot band around each outbuilding, the mowed strip around the propane tank and the cleared ground around the woodpile all need to connect without a continuous path of fuel between them. On acreage that often means one maintained, mowed and thinned core area holding the house and its nearby buildings, with the driveway and paths as breaks. Our propane tank guide and lawn and irrigation guide cover two of those pieces, and our acreage fuel break guide covers larger properties.

A free assessment is a good way to see your outbuildings the way a fire professional does: the Missoula Fire Department offers free defensible space consultations in the Missoula wildland-urban interface (406-552-6210), and Montana DNRC offers a free wildfire risk assessment statewide. This guide is part of our Montana Wildfire & Defensible Space Guide. HJ Property Care & Tree Service does the clearing, gravel, mowing, tree pruning and fire mitigation work around sheds, shops and outbuildings across Missoula County and the Bitterroot Valley. Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate and we will walk the property with you.

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