Who, what, why: Is it worth lightning-proofing UK homes?
Dramatic lightning strikes in the UK have acted as a reminder of the damage that can be done by electrical storms. When does it make sense to install lightning protection on homes?
Over the weekend homes in Essex, Gloucestershire, Kent and the West Midlands were damaged by lightning. Following a strike a major blaze in Rotherham, South Yorkshire was captured on video, as was the moment one house in Tunbridge Wells was hit. Householders might be forgiven for investigating whether installing lightning protection is worthwhile.
- The UK has a low rate of lightning activity compared with other countries
- "Rolling sphere" method used to assess whether buildings are at risk
- Buildings which are tall relative to those around them are most likely to need lightning protection
Generally the UK experiences a very low level of lightning activity by international standards, according to Manu Haddad, professor of electrical engineering at Cardiff University. There are approximately 0.46 lightning strikes per square km each year. This is very low compared to tropical regions. In some parts of Brazil the figure might be as high as 300. "What we've had over the past three days is what they have on a daily basis," Haddad says. The south-east of England does have a slightly higher incidence of lightning than the rest of the UK due to its warmer climate.
Lightning specialists use the so-called "rolling sphere" technique, which is based on electro-geometric modelling, to carry out risk assessments on buildings. An imaginary sphere 50m in radius is visualised rolling above an area. "The first object the the sphere touches, that will be the first point of impact for lightning," says Haddad. So buildings which are taller than those around them are most at risk.
Tall buildings will typically be installed with lightning protection spikes on the roof attached to copper tape along which the electrical charge runs to the ground. The cost of installing such a system on a home can vary considerably, but it might come to between £1,500 and £3,000.
Every property will need its own risk assessment to judge whether this sort of equipment is cost-effective. Having been hit in the past is no guarantee that a home will be safe in the future. Contrary to received wisdom, it isn't true that lightning never strikes twice.
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