Can Lightning Damage a Roof?

Where lightning goes on a house

Lightning looks for the easiest path to the ground, and on a house that usually starts at the highest and most pointed part. That means chimneys, aerials, ridges and any metal that rises above the roofline. The current runs down through whatever conducts it best: a damp chimney flue, an aerial cable, the metal of a gutter or downpipe, or the wiring. Along the way it can heat water inside brick or mortar until it turns to steam and bursts the material apart.

This is why strikes on houses often show up as a damaged chimney stack. Bricks may be thrown off, the pot may be cracked, and the flaunching, the mortar cap that holds the pot, may be shattered. Sometimes the first sign is debris on the ground, and sometimes the stack still looks whole but has been split inside.

What to look for from the ground

Stand well back and look at the roof, using binoculars if you have them. Do not climb up. Signs of a strike or a near miss include:

• broken or missing tiles, or tiles thrown some distance onto the garden
• cracks in a chimney stack, a leaning pot or missing bricks
• black or brown scorch marks on tiles, brickwork or fascia boards
• a damaged aerial or dish, or a burnt cable
• splintered timber at the eaves or bargeboards (the boards that finish a gable end)

Inside, look for scorched sockets, a tripped consumer unit, and ceiling stains. Switch off appliances you suspect, and get an electrician to inspect the wiring before you use it again.

Hidden damage

The worst damage can be out of sight. A strike can crack the roof timbers or make a small fire in the insulation, and these may smoulder for a time. If you smell burning, see smoke or find warm spots on a ceiling, call the fire service on 999. Even if nothing looks wrong, have the roof and chimney looked at after a strike, since cracks in a stack let water in and weaken the structure over time. A chimney with a cracked flue can also be a hazard when the fire is lit.

Is lightning damage covered by insurance?

Lightning is usually listed as an insured risk on home buildings policies, but read your own policy, since terms differ. Take dated photographs of every item, keep any broken parts, and get a written report from the roofer or builder who inspects it. Our page on the evidence your insurer needs after roof damage sets out what to collect, and the main guide on claiming for a leaking roof covers the claim itself.

What we do after a strike

We survey the roof and chimney, photograph the damage, and tell you what is loose, cracked or leaking. The repair might be a few replacement tiles, rebuilding part of a stack, a new pot and flaunching, or work to the timbers. Where the roof has holes, we can arrange a temporary cover and put emergency calls first, as set out in our storm damage to roofs guide. A price in writing, fixed, comes after the survey. The wider service is covered under emergency and general roof repairs.

Near misses and indirect damage

A house does not have to be struck to suffer. A strike on a nearby tree, pole or building can send a surge down cables and through the ground, and the effects show up as a fried router, a dead aerial socket or a tripped breaker. Lightning near a tree can also split the trunk or send a limb onto a roof, which is a separate problem with its own checks. If the tiles are intact but you heard a loud crack, it is still worth a visual check of the chimney and aerial. Photographs from the ground with a zoom lens often show a cracked pot or a lifted tile.

Tall, isolated houses on higher ground are more exposed. Parts of north Hampshire and west Berkshire have open ridges where the wind and weather meet the roofs directly, so the risk is not equal everywhere.

Protecting a house from a strike

A lightning protection system is a set of rods and conductors that give the current a safe path to earth. They are installed by specialists to a British Standard and are uncommon on ordinary houses, but may suit a tall or exposed building. Surge protection in the consumer unit helps guard electrics against nearby strikes. A roofer does not fit these systems, but we can advise where a conductor would run over the roof covering.