Will a Slate Roof Stop Lightning?

Lightning Strikes

• Lightning consists of negative and positive electrical energy. When lightning strikes, it is created by a negative charge present in the bottom part of clouds closest to the ground. A positive charge is present beneath the ground directly below the cloud. Between these two charges is a non-conductive area of dry air. As the opposite charges build, this dry air becomes moist and lightning travels toward the earth as the positive ground charge is drawn upward. When a lightning protection system is in place, the positive charge uses that system as an outlet. When the negative charge is near the top of your home, the positive ground charge travels through your lightning rod toward it. When it meets the negative charge, the opposing charges neutralize each other, and they’re dispelled safely into the ground.

Fire Protection

• Slate does provide some protection in the event of a lightning strike because it is fireproof, and in comparison to other roofing materials, it is one of the most fire-resistant roofs available. Should lightning strike, the slate will not ignite, but this doesn’t mean a fire can't start without a lightning protection system. The wood used beneath the slate to build the roof deck is not fireproof. In the event of a lightning strike, a stray spark hitting an area of roof that is not covered, or jumping to an adjacent home can cause fire.

Damage

• Slate is an extremely solid material, impervious to most climatic elements. While it will not stop the energy a lightning strike carries, slate is able to withstand high impacts better than materials such as shingles or steel without significant damage. While these other roofing materials may disintegrate or ignite when struck by lightning, slate roofs are more likely to crack if hit. While this won't prevent a lightning strike, it can limit the amount of damage caused.

Factors That Make Your Home Vulnerable

• The energy that a lightning strike carries can cause significant damage if it is not dissipated into the ground. Electrical systems, computers, and air-conditioning systems are vulnerable to even low electrical currents. When lightning strikes your roof without a protection system, it may flow through the roofing material and into these systems causing significant damage that can include fire. Homes that are the highest in a particular area, such as those built on hills, are more vulnerable to lightning strikes than those built on lower land around them. Larger homes, and those with steeples, cupolas, aerials, or that are surrounded by tall trees, are also more vulnerable than homes without these features.