Many thatched house owners have been told that their roofs should last 30-40 years but it is hard to put an exact lifespan on a thatched roof as each thatched roof will vary depending on different factors.
The main factors are:
The pitch – the steeper the pitch faster the roof can shed water.
In cases of roofs with dormers and valleys, the dormers and valleys will wear before the main coat, due to having a lower pitch.
If the roof is sheltered by trees or other obstructions in the winter time when the sun is low in the sky the roof will not always see the sun to dry out the roof if wet. This can promote moss on the coat, which when wet will hold water like a sponge and promote rot on that section of the coat. A ridge is generally replaced every 7 years.
Following the tips in my maintenance section will help prolong the life of your roof.