Slate Roofing

crystic roof sample imageSlate roofs can last decades without the need for a re-roof. the steel nails holding the slate  in position will fail long before any sign of slate erosion becomes a problem.

On ocassion slates will slip down a roof, causing rainwater to penetrate the building. This  may simply be due to incorrect fixing of the slate and can quite easily be fixed back into position. With a bit of maintenance like this you can prolong the lifespan of your roof and stop  any damage occurring to ceilings and the roof timbers on your property.

Sometimes, as i've pointed out, the steel nails holding your slate in position may have begun to fail. If this is the case, then the roof will sooner or later need to be replaced.

There is no need to panic at this stage, envisaging a total replacement of everything on  your roof.

The general condition of the slate on an average roof means you can usually salvage and re-use roughly 75%-85% of the slate on your roof when carrying out a re-roof If it's any less than this we will always advise you of this on 1st inspection of your roof, using pictures for you to view and terms you can understand.

We will not bog you down with  anything but our honest opinion of the condition of your roof and the simplest and most cost effective way of remedying it.

Types of Slate

The geology of slate is important, as it affects the appearance and longevity of the finished roof. Often the word “slate” has been used to describe mudstone, limestone and other types of roofing stone. However their properties are significantly different, requiring a different method of use.

The most common, and strongest, type of slate comes from metamorphic rock, which has been exposed to immense heat and pressure over millions of years. This gives good slate some useful properties:

  • It can be split thinly, reducing the weight of the roof.
  • Low water absorption: reducing the risk of frost damage, permitting an extremely long service life, and excellent durability
  • Hardness: reducing the mass of material required. Compared with natural slates, concrete or clay tiles are substantially thicker. A flawless slate has a distinctive ring when struck.
  • Workability: Slate can be cut, holed and trimmed using hand tools, making for fast, safe work when completing the roof.


Slates from the UK, Spain, Canada and China are produced from metamorphic deposits. These seams can contain twists produced by geological activity, and part of the skill of production is in making the best finished slates from that seam.

Why Use Natural Slate?

Natural slate is one of the world’s oldest continuously used roofing materials, with many of the world’s oldest surviving buildings roofed with slate. The durability of good slates is demonstrated by the fact a great many reclaimed slates are installed on re-roofing projects after decades of previous use.

The Carbon Footprint of natural slate compares well with other roofing materials- particularly when the life expectancy of the finished roof is considered. Some studies estimate the embodied carbon (per m2 of roof) at only 16% that of concrete tiles, the next-best roofing material. This reduced environmental impact makes natural slate an even more attractive choice for the new build and self build customer.

Natural Slate has stunning aesthetic appeal, from premium slates such as:

  • Penrhyn Heather Blue
  • Westmoreland greens
  • Burlington blues
  • blue-grey or blue-black Spanish slates
  • grey Chinese
  • grey-green Spanish & Brazilian.


The most common roof slating method is with “tally slates”, where identically-sized slates are laid broken-bond, and overlapped in a method similar to plain tiles. An even more traditional pitched roof covering is “Random slate”, whether the random element is width only, or both width and length.

History of Slate

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. Slate is a totally natural product that has been used for centuries!

Historical Mining Terminology

Before the mid 19th century, the terms slate, shale and schist were not sharply distinguished. In the context of underground coal mining, the term slate was commonly used to refer to shale well into the 20th century, For example, roof slate refers to shale above a coal seam, and draw slate refers to roof slate that falls from the mine roof as the coal is removed.

Slate in buildings

Slate can be made into roofing slates, also called roofing shingles, installed by a slater. Slate has two lines of breakability: cleavage and grain, which make it possible to split the stone into thin sheets. When broken, slate retains a natural appearance while remaining relatively flat and easily stackable.

Slate tiles are often used for interior and exterior flooring, stairs, walkways, and wall cladding. Tiles are installed and set on mortar and grouted along the edges. Chemical sealants are often used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence, and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation. Slate flooring can however be slippery when used in external locations subject to rain.

Slate tiles were used in 19th century UK building construction (apart from roofs) and in slate quarrying areas such as Bethesda, Wales there are still many buildings wholly constructed of slate. Slates can also be set into walls to provide a rudimentary damp-proof membrane. Small offcuts are used as shims to level floor joists. In areas where slate is plentiful it is also used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone.

Why use Slate

Aesthetics: Slate roofs come in a wide variety of sizes, colours, and thicknesses. One can create many different looks to enhance just about any architectural style.

Ecological considerations: Slate is a natural product that comes out of the ground and can safely go back into the ground. Petrochemical roofing made of asphalt and fibreglass typically lasts twenty years. According to statistics, construction and demolition debris make up 28% (by weight and volume) of the refuse being placed in landfills. That is more than the waste from Styrofoam, fast-food packaging, disposable diapers, and all plastic packaging combined! Approximately 20% of all construction debris is roofing. Though not the only reason, environmental concern is certainly a good reason for installing slate.

Effective protection: A slate roof is the best chance you have for getting a leak-free roof. Most leaks in roofs occur in flat areas and areas with protrusions. Since slate roofs are installed by craftsmen who are thinking in service life of decades or even centuries, these details are usually installed with great care. As a result, the quality of leak protection is much higher. Thus slate roofs leak much less often than other kinds of roofing -- especially on houses with complicated roof lines. Slate roofs are one of the most fireproof roofs. Slate roofs are much more wind resistant than asphalt roofs. Slate roofs also do not rely on the underlying roofing felt to remain leak proof the way many clay and concrete tile roofs do.

Long-term Reliability: Slate has been the material of choice for a large percentage of the most important buildings built in the last five centuries. The method of installation has changed little over five centuries. New roofing products, such as many of the simulated slates, have come and gone in less time than asphalt roofs last. Some of these products have been sold with 50-year warranties, which became worthless when the businesses went under.

Slate roofs are fireproof: Slate itself is fireproof. A slate roof is one of the most fire resistant roofs that exist. However, the wood deck under the slate is not fireproof. Often fires will jump from house to house as sparks hit adjacent roofs, igniting the surface if it is a flammable material. Many of the raging fires that engulf hundreds of houses every year would not occur if the houses were covered in slate.

So all in all Natural Roof Slate is the most fireproof; aesthetically pleasing, reliable and ecologically sound roof covering around!