Tradition under threat

The geology of a region shapes not just the landscape but its architecture. Local stone sources strongly influence the character of buildings, particularly those in villages remote from large cities, achieving a unique visual harmony in locations such as the Pennines and the Cotswolds. However, these types of local building style, or vernacular, are at risk from a scarcity of sources of local stone, dwindling expertise, and the limited availability of training. Stone roof tiles, for example, require specific skills in both their production and use. To retain these skills – which are a critical part of our heritage – requires reinvestment in training and the resumption of stone tile production (Hughes et al., 2003). Roofing companies, particularly those specialising in conservation and heritage work, have an essential role to play in training the next generation of craftspeople.

Scarce sources

Stone used for roofing is commonly referred to as ‘stone slate’. However, this nomenclature is inaccurate, especially if one considers that most stone (as opposed to slate) used in roofs in Britain is derived from sedimentary rocks, principally sandstones or limestones, splitting along a bedding plane rather than a cleavage as would be the case for a metamorphic slate. For geological correctness, geologists prefer the term tilestone or stone tiles for sandstone and limestone used in roofing (to distinguish it from slate). Here ‘stone tile’ is taken as sedimentary stone.

Historically, building stone and stone tiles would be extracted from small quarries worked episodically to meet local demand.

Whilst less hard-wearing than slate, stone tiles themselves are durable. However, the underlying roofing felts inevitably deteriorate, leading to leaks and possible decay of the roof timbers, necessitating ongoing maintenance and repairs, and occasional re-roofing. Most stone tiles can be reused, but some will crack or delaminate, requiring replacements. Replacement tiles should ideally be sourced locally, using stone with the same geological properties, perhaps salvaged from a previous former building.

Historically, building stone and stone tiles would be extracted from small quarries worked episodically to meet local demand. Even then, stone from the same quarry (or the same strata in a nearby quarry) can vary in quality and characteristics, which historically meant that roofs changed over time as different sections of a quarry were worked. Currently, there are very few building stone quarries and fewer still that can also produce stone tiles. This rarity is partly a reflection of planning laws that prevent local extraction without planning permission, and partly relates to economics – the small-scale local stone and tile quarries of the past would be uneconomic to establish and operate today.

Stone roofing

Skilled roofers blend tiles of various sizes and textures to defend against the worst of the elements. Traditional stone roofing techniques are quite regionalised in Britain, having evolved in response to both the local climatic conditions and geological characteristics, which influence stone-tile production, roof design and the detailing of stone tile installation. Compare, for example, the Carboniferous sandstone roof tiles of the southwest Pennines with the Jurassic limestone roof tiles of the Cotswolds.

In both the Pennines and the Cotswolds, traditional stone tile roofs are often laid using diminishing courses, with tiles arranged in decreasing sizes towards the roof apex. This method, which originated as a practical response to the varying sizes of stones available from local quarries, requires specialist skills. Roofers must be able to dress the stone, set out the courses, and peg the tiles (traditionally using wooden pegs, though modern roofers often use alloy, aluminium or copper dependent upon stone tile type).

Southwest Pennines

Waukmill Farm in Rainow, Cheshire, UK (Image credit: Raymond Knapman, CC BY-SA 2.0, via Wikimedia Commons)

A personal experience in re-roofing the Kerridge stone (Carboniferous Milnrow Sandstone) tiled roof of a property in Rainow, southwest Pennines, highlighted three key issues of scarcity of local stone, dwindling expertise, and limited training. Finding skilled roofers with expertise in laying stone tiles is increasingly difficult. Local quarries are producing less stone (at least in the southwest Pennines), and while some roofers build up their own supply of reclaimed roofing tiles, or have access to a supply of reclaimed stone, these stocks are limited.

There are few training programmes or apprenticeships in traditional roofing methods. While a Heritage Skills NVQ Diploma Level 3 in Roof Slating and Tiling is available (www.stoneroof.org.uk), this course alone cannot fully address the need for training in these ancient techniques, leaving little opportunity for the next generation to learn these vital skills.

Adapting for the future

To ensure that traditional stone roofs remain a viable choice for future generations, we must balance heritage preservation with modern requirements. For example, traditional stone roofing techniques must adapt to modern needs, particularly with regard to insulation and ventilation,  without compromising the historical appearance of the roofs.

While advice on roof appearance and suitable stone is available (e.g. Historic England, 2005), there is a lack of technical guidance or standards in the form of codes specifically for traditional stone roofing practices. Modern roofing standards are not easily applicable to differently sized stone tiles – specific codes are needed (Woods, 2017).

Reinvestment in local materials and traditional skills is urgently needed

Traditional stone roofing is under threat from a combination of pressures. To preserve this vital part of our architectural heritage, reinvestment in local materials and traditional skills is urgently needed. With the right support, the unique stone-tiled roofs of the Pennines, the Cotswolds and beyond can continue to protect homes and tell the story of their region for centuries to come.

Author

Dr Colin Serridge

Senior Lecturer in Earth Sciences at Edge Hill University, UK and Engineering Geologist in the Specialist Ground Improvement industry

Further Reading

• Derbyshire County Council (1996) Derbyshire Stone Slate Roofs: Guidance for Owners of Historic Buildings, Matlock; derbyshire.gov.uk
• English Heritage (now Historic England) (2005) Stone slate roofing: Technical advice note; historicengland.org.uk
• Hughes, T.G. et al. (Eds) (2003) Saving stone slate roofs: the revival and enhancement of the stone slate roofing industry in the South Pennines, a model area of Britain. English Heritage Research Transactions, 9, James and James, London.
• Stone Roofing Association; http://www.stoneroof.org.uk
• Wood, C. (2017) The time has come for a Code of Practice for Historic Roofs. Roofing Today 70, 8; roofingtoday.co.uk

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