Longevity and value The quality of Welsh slate roofing is such that even after 100 years of use at least 50% of Welsh slate is typically re-used. There are buildings around the world which have Welsh slate roofing tiles which are several hundred years old. There is no other roofing material which has demonstrated this extraordinary durability. The result of this longevity is that Welsh slate is a very cost effective roofing material as it is less costly to maintain and has a lower frequency of re-roofing. In addition a second hand Welsh slate has a typical value of 60% of a new slate.