Slate is the longest lasting and most durable roofing material available. Mined in countries around the world, it has been used for centuries as a reliable, weather resistant and fireproof roofing material. Different slates have differing longevity. Being aware of the country of origin of the slate and using a qualified slate roof installer adds to the longevity of a roof covered with slate.
Number 10 Downing Street and Buckingham Palace both have Welsh slate roofs that are expected to last approximately 150 years. New and used slate tiles are fireproof, and as a naturally mined product, are environmentally friendly. Welsh slate withstands cold and rain. Using copper nails adds to the longevity of the slate roof.
New York, Vermont, Maine, Maryland, Virginia and Pennsylvania have slate quarries and produce most of the slate roofing tiles found in new and old American buildings. Most American slates are hard and life expectancy is estimated at up to 200 years. Pennsylvania black slate is softer and should last 75 to 125 years.
Glendyne/Glacier slate originates in Canada. Its composition makes the tiles resistant to frost. Canadian slate is free of oxides, which means the shine of the tiles lasts the lifetime of the slate. Canadian slate roofs are known to last more than 100 years.
Mined in a climate warmer than most slate-producing countries, Spanish slate's composition is different than the colder-climate slates. It contains pyrite, which causes the slate to bleed veins of rust. Spanish slate is also soft, with uneven graining, causing it to split. Spanish slate roofs, if problem free, can last 40 to 50 years.
High in iron oxide, Chinese slate can rust. Its composition is brittle and the tiles are susceptible to cracking. It is also soft and is not durable in cold climates. Pallets of Chinese slate differ in composition and colour, and it is important to verify that the slate ordered all comes from the same mine and was mined at the same time to prevent a variety of slate colours on the roof. A Chinese slate roof has a life expectancy of 60 years.
Composite slate is not a natural product. It features a smooth surface. It is not fireproof or weather resistant. While it looks similar to natural slate, weathering can alter the appearance of roof covered in the composite in approximately 10 years.