With proper maintenance, a thatched roof will last around 70 years before it needs to be replaced. The ridge will need to be maintained every 10 to 20 years.
A thatched roof is built on a 45-degree angle and made from a waxy material that helps repel water. It is built very densely, deterring pests, and is affixed to the rafters, making it a permanent part of the home. This makes it strong enough to withstand heavy storms.
A thatched roof may be added to an existing home, but if the roof isn't sloped enough to create a 45-degree angle, parts may have to be built up to help provide a watertight seal around the home.