There is a limited range of materials that roof tiles can be made of, and it won’t be obvious from ground level which you choose. Modern, factory made tiles will look just like stone or clay equivalents.
Natural Slate:
Slate is a fine grained metamorphic rock. It was formed millions of years ago when ocean or riverbed sediments were compressed over time by the earth’s crust. There are natural slate quarries around the world: in the UK the main slate quarries are in Wales and the North West of England.
The formation of slate allows it to be “cut” by striking the material with a specialized tool to produce flat sheets of stone. It is this flat sheet characteristic that made slate one of the earliest materials used for hard roofing materials.
Slate is fundamentally grey in colour but the grey can vary widely in shade from pale to dark and it may also have a purple, green or blue hue.
In the Victorian era slate was a widely used and relatively cheap material for roof coverings. As the easily accessible slate mines have been exhausted the material has become increasingly expensive. Suppliers of slate roof tiles may have to import products from places as far afield as China or India.
Modern equivalents (such as Redland’s Cambrian range) will use recycled slate combined with resin to give a product that looks like natural slate but at a much lower cost.
Natural Stone:
Natural stones (usually sandstone or limestone) have also traditionally been used for roof tiles. This is most common in the North of England and Scotland where local stone was particularly suited to this use.
Today, any type of natural stone will come with a hefty price tag. It is generally used only in areas of particular architectural interest. The best example of this is the Cotswolds where many developments close to historic villages will be built entirely out of Cotswold stone (which is a limestone).
Clay:
Clay is one of the oldest building materials on earth. Clay is a naturally occurring mineral which is naturally pliable but which hardens when dried or fired.
Clay roof tiles will be produced in a mould and, because they are made of a naturally occurring material, they will include attractive colour variations and will not be entirely regular in texture and dimension.
Clay roof tiles have always been particularly popular in the South of the UK where clay deposits are most common, and the colour variation in clay roof tiles reflects variations in the local clay deposits.
The material is a popular choice for architects who like its traditional, rustic, irregularity and is frequently used on larger, high-value new homes.
Concrete:
Contrary to popular belief, concrete is not a new material – in fact the romans were the first to use it. Concrete is a composite material made from cement, other cementitious materials (such as fly ash), aggregate (such as gravel or crushed rocks and sand) with water.
Concrete solidifies and hardens after mixing with water. The water reacts with the cement to bond the other components together to create a robust, stone-like material. Concrete is used more than any other man-made material in the world.
Concrete roof tiles have been manufactured in the UK for nearly 100 years and it is now the most common material for new roofs.
The natural colour of concrete is grey, but using coloured sands in the manufacturing process means that concrete roof tiles can be made to faithfully imitate the colour of naturally occurring clays or stones.
The manufacturing of concrete tiles can be rigorously controlled, ensuring that the end result is technically accurate and very consistent. As the products are manufactured in large quantities, the cost of concrete roof tiles will always be lower than clay, slate or stone equivalents.
As environmental considerations become increasingly important, so concrete is also gaining new enthusiasts. One important factor is the embodied energy of building materials: this is calculated by working out the energy required to manufacture the product and the carbon dioxide created by the manufacturing.
Redand, which manufactures both clay and concrete tiles, commissioned engineering consultants Ove Arup and Partners Ltd to analyse the carbon dioxide emissions of its operations.
When looking at the manufacturing process, the key factor is the firing process: clay tiles must be fired at very high temperatures (around 1,000oC) – an energy intensive process. In contrast, just adding water and curing at less than 100oC achieves the necessary strength for concrete tiles.
The end result is that the embodied energy of concrete tiles is approximately half that of equivalent clay tiles – a fact that is likely to become increasingly significant in the specification of building products in the future.
