Lifespan of Welsh Slate
The quality, performance and durability of roofing slate can vary enormously. The lifespan of slate in Australia may be as short as 10 years or longer than 150 years depending on the origin of the slate that is used and the quality of building design and workmanship.
The only slate that is known to perform 150 years or more under Australian conditions is Welsh Penrhyn http://www.welshslate.com – a slate that came to Australia as ballast in trading vessels the early 1800s.
Condensation in roofs is a major cause of slate and batten failure. Irrespective of slate quality, the performance of a slate roof is at the mercy of architects and builders – ventilation of the roof cavity is a critical determinant of longevity. Slate lying directly on boards or close to sarking is likely to have a shorter lifespan. A free flowing cushion of air under the slate is vital to avoid moisture build-up causing deterioration to the underside of the slate.
Quite often moisture build-up from condensation will rot out battens long before the slate is affected. Ultimately, slates too will perish from excessive condensation – it will just take longer because of their density and water resistance.