What causes attic fires?
Short answer. Most attic fires start with electrical problems, such as damaged or overloaded wiring, rodent-chewed cables, or recessed lights buried in insulation they are not rated for. Others come from flues and chimneys too close to wood framing, lightning strikes, attic equipment like furnaces and fans, and embers entering through vents from an outside fire.
The usual sources
- Wiring: old or amateur splices made outside junction boxes, overloaded circuits, and cables crushed or nailed through. Attic heat also ages wire insulation faster.
- Rodents: squirrels and rats chew wire insulation. In North Georgia, where squirrels get into attics often, check the wiring whenever you find droppings.
- Recessed lights: older fixtures not rated for insulation contact can overheat when buried. IC rated fixtures can touch insulation; others need clearance.
- Flues and chimneys: metal flues from gas appliances need specified clearance from wood, and a cracked masonry chimney can let heat or sparks reach framing.
- Equipment: furnaces and air handlers in the attic, and attic fan motors. Many power fans include a high temperature cutoff so the fan stops rather than feeding a fire.
- Lightning: a strike can ignite framing directly or travel along wiring and metal.
- Outside fires: embers can enter through gable and soffit vents, which is one reason vent screening matters.
Reducing the risk
Have an electrician look at any attic wiring that is loose, spliced without boxes, or chewed. Keep insulation and stored boxes clear of flues and non-IC light fixtures. Close animal entry points so the wiring does not become a chew toy. Keep smoke alarms working, and keep stored items well away from any attic furnace and its flue.
Roof work affects some of these too. A reroof should reflash metal flues with proper storm collars and keep flammable materials clear of them; see roof flashing explained and chimney leaks and crickets.