It is due to this durability that roof slate can be considered truly “green” or environmentally friendly. Other roof coverings may have to be replaced many times in the life of a similar slate roof increasing carbon emissions. The material is formed when rock is forced into thin sheets by intense pressure. In the past slate produced in the United Kingdom came from five main areas. Wales, West Morland, Cumberland, Lancashire, and Cornwall all produced quality roofing slates. Today the majority are imported from Spain and China.
Categories and sizes
Roofing Slates used to be categorised by quality. In descending order of quality these are bests, seconds, thirds and tons. The majority of builders and roofing merchants will now categorise the materials by size and origin. The sizes range from 24 inches by 14 inches down to 10 inches by 16 inches. Generally speaking, the larger sizes are used on bigger builds or to provide increased coverage towards the bottom of the roof. When building a new roof, consideration should be given to the local climate. Due to the way water travels over a roof slate, (the angle of creep) larger sizes are more suitable for wetter climates.
Buying new roof slates
A premium slate roof carries a hefty price tag. Welsh slates are generally considered to be the best on the market. In terms of appearance and durability they are second to none. Unfortunately, at three to four pounds each the cost can be prohibitive. Depending on the size of the structure, you will need between one and two thousand to complete a home. Add to this the fitting costs and you have what may seem an expensive roof. However, if you take into account the life span of the roof over cheaper alternatives, the cost is reasonable. Burlington and Westmorland are slightly cheaper and of a similar quality to Welsh roof slates. Spanish slates offer a good alternative if the budget needs to be trimmed. At half the price they are still a quality slate, although they have not yet stood the test of time. Chinese slates are cheaper still but many experienced roofer’s have complained about the brittleness of the product.
Reclaimed roofing materials offer an environmentally friendly alternative to your roof covering. If chosen correctly used slates will provide an attractive and durable roof. You should expect to pay about two pounds each for good reclaimed Welsh slates. As well as uniformity and appearance it is advisable to test reclaimed slates for absorption. A simple test can be carried out by standing the slate upright in a large bucket. The bucket is then filled with water halfway up the length of the slate and left for 12 hours. Due to absorption the water line on the slate will rise higher than the water level in the bucket. The higher the water line the greater the absorption. It should rise no more than a quarter of an inch. Any slates that fail the absorption test should not be used for roofing as they will not provide a weather tight seal. If the slate has started to delaminate it should also be discarded. When cut in half they should be solid with no flaky layers.
Man made roofing slates
Composite roofing is manufactured from various plastics to mimic traditional roof materials. It offers a number of benefits including the price. Costing a quarter of the price, composite roofing is also more robust during construction. This saves wastage costs. They can be dropped and cut without fear of breakage. As for appearance, from the ground you would be hard pressed to tell the difference. The shape has been moulded to give the appearance of a weathered roof. Composite tiles are significantly lighter so they can be used on weaker structures. On the down side, early examples proved far less durable once fitted. Some composite tiles fitted within the last twenty years have started to fade, resulting in patchy roofs. The bottom or tail of the tile was also subject to curl in areas of high UV light. Manufacturers have overcome these early problems and some composite slates now come with an impressive lifetime guarantee.
As with most purchases, you pretty much get what you pay for. Choose your roof covering according to your budget and the longevity you require.