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It is essential to act now if we are to secure the unique history and architectural character of England's roofs.
Conservation Issues
Disappearing Skills
Practical Issues
Saving our Stone Slate Roofs
Stone Slate: A Sustainable Product for the New Millenium
Pennine Gritstone roof
Wherever rock could be split to provide thin enough slabs it was used for roofing
The extraordinary richness of England’s built heritage is a reminder of our ingenuity in response to our surroundings and their particular environmental and  eographical characteristics. The roofs and walls of historic buildings are clues to the geology of the surrounding landscape, and demonstrate the skill by which the local population used available resources to provide shelter thereby developing the vernacular or traditional local buildings we now cherish. Local character and distinctiveness is under threat and limestone and sandstone roofing is becoming increasingly rare. If the erosion of regional identity is to be arrested, measures need to be taken to ensure local materials are made available.
Stone slate roofs are a fundamental part of the distinctive local character of vernacular buildings in many parts of the country. Their solid beauty achieves a  visual harmony with the stone buildings and the drystone walls of the fields which makes areas such as the Cotswolds and the Pennines unique.
Stone slates are known in different parts of the country as grey slates, flags, flagstones, thackstones, slats, flatstones, stone tiles and tilestones. Geologists prefer the term tilestone as these sandstone and limestone products are not geologically slates. That is, they are sedimentary rather than metamorphic and  consequently split along a bedding rather than a cleavage plane. Stone slate however, is historically the most widely and understood term.
The properties of the rock are expressed in the details of the roof
Large slates need mitred valleys in this case a chevron type
Large slates need mitred valleys in this case a chevron type
Small slates are used in swept valleys
Small slates are used in swept valleys
The slaters’ skill and style of working the raw material contributes to the local and regional distinctiveness of stone roofs, but the character of the roof is derived principally from the colour and texture of the stone slates, their size, thickness and roughness. The nature of the rock dictates the manner in which it can be worked, the treatment of the hips, valleys, ridges, dormers, eaves and abutments of the roof. The aim is to resist the weather, but the craftsperson's artistry and understanding of the materials determines the expression.
The differences in colour and texture in the sedimentary rock from which the slates are made arise from the conditions in which the beds were deposited millions of years ago. Shallow water produced a rippled stone. Deeper, calmer waters produced flatter smoother and generally larger slates. In slow moving water the sand particles are smaller and the slates’ texture is finer, and less grainy. The variety of colours from pale yellow to red, which is a result of iron staining, together with the variety in texture, imparts the local distinctiveness, which can vary from village to village. Until improvements in transport made it easy to import cheaper, mass produced products, each village used its local stones, providing its buildings with a distinctive local fingerprint.
Stone slates have always been laid in courses diminishing in size from the eaves (where the slates can be up to four feet long) to the smaller stones at the ridge (which may be as small as four inches long). This careful sizing of the slates reflects the character of the rock and the selection of sizes which could be made. It reduced wastage by ensuring even the smallest stones could be used. 
Stone slate quarrying is a small scale operation, which generally exploited the relatively thin, near surface deposits. Quarrying occurred either; along the crest of a steep slope where the rock was parallel with the surface and could be reached with a minimum of digging or using an open pit method. The latter is the usual method in southern England. In rare cases, such as the Collyweston in Northamptonshire, the stone was only found at a depth which meant that it had to be mined. Here the unriven blocks of stone were stored underground until the promise of cold weather; the stone would then be brought out into the open so that the frost could split it into slates.
Extraction for stone slates remains low tech, which reflects the nature of slate and the need to produce slabs which are as large as possible. Historically all the extraction processes were by hand; horse or man-powered mechanisation was only adopted in the largest workings in the form of narrow gauge rail systems.
Rock unsuitable for roofing was made into flooring, flagging, kerbs and walling stones, a range of products which resulted in the visual harmony between the architecture and the landscape. Conversion of the rock to roofing slates was traditionally; entirely done by hand and remains so for most of the steps involved. The stone is split to the desired thickness with a chisel or by ‘frosting’. The edges are then trimmed square and bevelled with a hammer.
Inappropriate repairs destroy the visual harmony.
If any regard is to be had to the general beauty of the landscape, the natural material of the special countryside should be used instead of imported material. William Morris 1890
Stone slates have been used since Roman times. Originally used as a prestigious alternative to thatch, stone slates eventually, became a standard roofing material. They make a unique contribution to the appearance of out towns and villages. Yet the qualities of colour and texture that they bring to the rural scene are vanishing before our eyes as old roofs are re-clad with inappropriate substitutes. The cycle of substitution by cheaper alternatives leading to declining production and increasing costs, has been a problem since the nineteenth century. Improvements in transport facilitated the importation of cheaper, alien products from the furthest corners of the country and beyond. The consequence has been that in many regions the production of stone slates ceased years ago, with the few remaining producers in a precarious position and largely dependent on indirect grant support through heritage bodies for their continued existence. The use of mass-produced products brings with it standardised roof details, so that buildings eventually look the same wherever you go.
This roof has been stolen three times.
This roof has been stolen and sold to other buildngs  three times
The options of using salvaged slates creates a market which encourages the removal of stone slates from their original location, and in the extreme may encourage theft. When local products disappear so do the slating traditions and with them the regional roofing character. 
Stone slates demand special skills in production and use, today there are few craftspeople able to offer such expertise. In times of rising unemployment in rural areas, we should take the opportunity to reinvest in these traditional local skills and at the same time ensure the preservation of our stone slate roofing tradition, a vital part of our heritage. The stone thackers as they were once known, blended the sizes and textures of the slates to create a defence against the worst of Britain’s weather. That skill at working with the stone is now disappearing as the material grows scarcer.
At present stone slating is not included in any of the NVQ courses available in this country; even in areas where the towns are dominated by stone slate roofs. There is a need for training to ensure that the best historical techniques are adapted to meet modern needs (such as insulation at ventilation) without compromising the roof’s traditional appearance. Likewise, there are few opportunities for architects, surveyors and others to learn the necessary skills to rebuild or repair a traditional stone slate roof so that it will last another two to three hundred years.
Training is needed in all areas of the stone slate industry. English Heritage is developing a training module, and a guidance leaflet for conservation practitioners. Roofing companies also have a role to play in the training of craftspeople. Educational establishments also need to be equipped to meet the challenge of the necessary training.
The objective is to conserve the distinctive regional appearance of roofs. This means choosing the correct materials and techniques to ensure that the roof will do its job. The detailing of the roof, its pitch and the treatment of the eaves, valleys, ridges and dormers - evolved in response to materials and climate, and may also vary according to the building type and its period. Correct detailing not only creates the character of the roof but also ensures that the roof performs satisfactorily. In the Cotswolds for example swept valleys are common as the small tapering slates fit comfortably into a curve. Conserving these vernacular traditions will ensure that neither the character nor the efficiency of the roof is lost.
Stone slate quarries were always small and supplied small local communities. The appearance of stone slates varies widely even within one geological bed. Rough or smooth, thick or thin, large or small, light or dark in colour: these factors give variety and expression to the roof. The preferred policy is therefore to encourage many small sources of supply rather than one large source. This has the advantage of reducing the impact on the environment. Where there is only a very small demand for a particular type of stone, the quarry can be operated intermittently, perhaps only for a few months over a period of several years.
The use of material salvaged from other old buildings should be avoided and new stone slates used wherever possible. Second hand slates should only be re-used on the building from which they were recovered. Tiles made from substitute materials such as fibre resin, artificial stone, or concrete should not be used on historic buildings.
The failure of a stone slate roof is usually caused by the failure of the nails or pegs used to fix the slates to the battens, the decay of battens or rafters, or lamination or cracking of the slates’ top edges. When reroofing, it is advisable to record the roof prior to stripping, to ensure that the existing details, such as the number of courses, are properly reinstated. Stripping should be carried out carefully to ensure that all sound stone slates remain undamaged so that they can be sorted according to type, size and thickness ready for re-use.
Roofs,walls,flags,curbs and setts.
Roof, walls, flags and curbs; the harmony of the vernacular tradition.
The decline of the stone slate industry in the South Pennines means that the fundamental visual character of the whole region is under threat. The unique Pennine landscape provided by the dry stone walls and stone cottages of the villages and towns, with their sturdy stone roofs, achieves a visual harmony with the rocky crags of the hills. This special character is gradually being eroded by the use of unsatisfactory substitute roofing material, or different stone from other regions.
To revive the industry English Heritage and its partners have taken the South Pennines as a model and carried out a two year research project into the resumption of stone slate roofing production in Derbyshire and the Peak District. The results are now providing a model for this national campaign. The research attempts to tackle the problem by: identifying the size of the market, examining the impact of current heritage and planning policies and the allocation of historic building grant aid, and determining where training and education is needed. The results provide information to manufacturers, specifiers and users and locates possible sites for small scale, minimal impact extraction of suitable stone.
By reviving the stone slate industry English Heritage and its partners aim to fulfil conservation goals at the same time as stimulating employment and the local economy. Stone slate extraction is a low energy industry producing a long lasting quality product, thus satisfying today's requirements for the use of environmentally friendly materials and sustainable development.
- stone slates are the epitome of a sustainable material. They last hundreds of years and are capable of almost continuous re-use
- the production of stone slates is energy efficient and because the industry is local, transport costs are low
- stone slate roofs are thermally efficient, keeping household bills down 
- durability makes stone slates one of the cheapest roof coverings over the long term; they will out perform mass-produced substitutes
- the revival of the stone slate industry will promote economic growth and employment opportunities
- demand can generally be supplied by re-opening old quarries which are small scale operations with low visual or environmental impact
- the production of new stone slates would help to defend existing stone slate roofs from the threat of dismantling and theft to satisfy local demand
- traditional skills currently on the verge of extinction, can be saved. Only the combination of hand and eye can maximise the output of slates from unpromising rock which gives stone slates their distinctive character stone slate quarries can also meet local demand for walling, kerbs, flag stones and other paving.
Stokesay Castle
Stokesay Castle, Shropshire