This section provides detail on the production of hand and machine made clay roof tiles as well as valuable technical information. It also presents information about the manufacturers' approach to addressing one of today's major concerns in the building industry - the SUSTAINABILITY of their products and processes. For detailed technical enquiries associated with the use of clay roof tiles please contact the manufacturer of the tiles in question (see CRTC members).

The final appearance of a tiled roof depends upon its pitch, the inclusion of dormers, hips and valleys, the detailing of gables, eaves and ridges and the colour and texture of the tiles. Developments in the production process have improved the physical quality, versatility and availability of clay roof tiles which are now widely regarded as a superior product commensurate in technical and pricing terms with alternative roofing materials. Clay tiles come in two main formats - plain tiles and profiled tiles. Like bricks, tiles can be cut by hand and by machine to fit even the most complex of shapes.

Did you know?

• Between them, the five manufacturing members of the Clay Roof Tile Council employ nearly 1,000 people, some using the same skills held by their predecessors in the 18th and 19th centuries.
• Clay roof tiles can be hand made or machine made.
• Hand made tiles have the characteristic irregularities that come from this traditional method of production in which pre-cut slabs of clay are hand thrown into moulds. There is also the inherent value of having a hand-made product carefully crafted using methods passed down through the centuries. All hand-made tiles are sand-faced finished as this substance is used to line the mould.
• Machine made tiles come with a choice of finishes - smooth-faced and sand-faced.
• Further design dimensions can be added to a property by using ornamental tiles such as the club bullnose or beavertail ornamental tiles, a fishtail shape or a pointed end, usually called diamond or arrowhead ornamentals.
• Some manufacturers of hand made clay roof tiles use the same process that has been passed down through the generations of workers for more than 250 years.

SUSTAINABLE ROOFING USING CLAY TILES

BACKGROUND

At the better Buildings Summit in October 2003 ministers announced the formation of a Sustainable Buildings Task Group to advise Government on practical and cost effective measures to improve the sustainability of buildings in the short and long term.

The Task Group report entitled Better Buildings – better lives made, which was published in May 2004, included thirty nine recommendations to government including a number relating to the establishment of a Code for Sustainable Buildings.

A Senior Steering Group led by the Office of the Deputy Prime Minister has produced an outline of the Code which will include energy performance, water performance, waste and materials requirements and serviceability requirements.  The Code will use the BRE Environmental Assessment Method BREEAM and build upon it especially with regard to water performance.  Although many of the subjects to be addressed are not directly influenced by the choice of roof covering some, for example maintenance of performance, re-use and recycling are relevant.

These recent developments follow on from the Sustainable Development Strategy in 1999 whereby sectors were encouraged to develop strategies for themselves based around the four areas defined by the government, namely social progress, environmental protection, natural resources and economic prosperity.  The industry sector is working with its trade organisations and as individual companies to address the elements of this strategy.  This is necessary and progress is achievable as it relates to the development of the manufacturing side of the industry which is under the control of the companies.  In many cases the progress which has been made in the clay brick sector which is a much larger sector in the UK has been drawn upon, some of the companies are in both sectors.

The development of the Code for Sustainable Buildings aims to bring greater balance to the whole case for sustainability which is after all about the manufacture of building materials to produce durable, high performance buildings which last using processes that do not restrict future generations from doing the same.  The Code will use BREEAM and in relation to housing, Ecohomes the BRE schemes for environmental ratings of buildings.  These in turn will use the summary ratings in the Green Guide to Specification to include the materials impacts on the overall environmental impact.  Considerable progress has been made on the rating systems with substantial industry input and so some of the very difficult judgements have been made.  For example, trying to balance mineral extraction and the use of fossil fuel with recyclability and human toxicity.  However for an energy intensive industry such as the manufacture of clay tiles it is felt that the Life Cycle aspects are not fairly reflected in the choice of 60 years as a replacement period.  Current discussions about the Code do refer to longer periods and clearly given current replacement policies, especially in housing we expect clay roofing tiles to last a lot longer.

So not to labour the point the plea is that whoever is taking a view about sustainability some balance is needed to acknowledge manufacturers efforts in, for example, social progress as well as in using the more independent ratings to ensure that sustainable development means just that from start to finish.

Against this background this document reviews some of the issues of relevance to sustainability for the clay roofing tile industry.  The opportunity has been taken to go a little beyond what is, if arguably, measurable to comment on what some would include in the broader definition of sustainability – does anybody like this building?

THE INDUSTRY

The market for clay construction products is about £670M within which tiles amount to some £48M and their manufacture involves some 550 people.

THE MANUFACTURING PROCESS

The majority of clay roof tiles in the UK are manufactured from locally sourced clay which is broken down by crushers and rollers to a fine particle size.  After water addition a strip of clay is extruded which is cut into small lengths or bats which are the pressed into the tile shapes.  Drying and firing are carried out in modern computer controlled dryers and kilns and handling is increasingly fully automated.  Little raw material is wasted as most is recycled back into the preparation and shaping end of the process.  As with most heavy clay processes heat that historically would have gone out of the chimney stack is recycled either into the pre-heat zone of the kiln or the dryer.  There are of course variants to this mass production approach and hand moulding of tiles in wooden moulds lined with sand as a release agent does occur typically at some of the smaller niche manufacturers in the South of England.  Flue gas emissions are controlled by gas scrubbing devices and in all cases the firing process is optimised so as to produce acceptably low levels of emission.  The results of this process are that UK produced tiles have good dimensional control, are impermeable and durable with good mechanical properties.

SUSTAINABLE DEVELOPMENT STRATEGY : THE CLAY TILE SECTOR

Social Progress

The clay tile industry is not a large employer and its factories range from the traditional producing hand made products to the highly mechanised with some robotic handling.  However, the factories often located in rural areas are significant local employers.  Consequently, the welfare and development of the personnel are important and the association with the much larger clay brick industry enables participation in schemes that might not be possible for the industry alone.

Employee Welfare

All member companies of the CRTC are party to the Ceramic Industry Health and Safety Pledge.  This ten year programme is designed to achieve defined levels of improvement in the incidence of work-related injury and ill-health.  Specific targets have been set:

• To reduce the number of working days lost per 100,000 workers from work-related injury and ill-health.
• To reduce the incidence of fatal or major injury accidents.
• To reduce the incidence of cases of work-related ill-health.

Accidents at Work

Participation by a company involves main board commitment and responsibility, and a structured approach to achieving continuous improvement measured by annual reviews using key performance indicators.

Training And Personnel Development

The Industry’s employees are encouraged to further their personal development through:

• Training programmes provided by companies to meet the particular needs of individuals.
• Sector specific packages supplied through Proskills, and formerly through the Refractories and Building Products Training Council and other specialist providers.
• A suite of industry NVQ’s.
• Membership of the Institute of Materials and participation in its professional development activities.

There is particular focus on the development of information technology skills, health and safety best practice, supervisory management and technical certification.  An industry modern apprenticeship scheme is currently being prepared.

Training And Personal Development

The Refractories and Building Products Training Council was until mid 2005 the industry training organisation for the UK sector of industry producing refractories and building products.  It now forms part of the new Process and Manufacturing Sector Skills Council, Proskills. The RBPTC offered a full range of NVQ’s for managers, operatives and technical staff, including assessor training and its successor has the potential to be even more effective.

The Institute of Materials (which now encompasses the erstwhile Institute of Clay Technology) is the industry’s professional body.  The ICM provides its members, through a network of regional branches, with professional development activities including the sharing of best practice through meetings, training, education, fellowship and well-informed communications.

A major part of the Institute’s current programme is the development of a syllabus and teaching material for a foundation and an advanced technical certificate in the manufacture of clayware, which will constitute a nationally recognised professional qualification in the core subject of clay technology.

In support of the sector in a broader sense the CRTC has published A Guide to Plain Tiling, including vertical tiling which is available freely and aimed at helping specifiers and users.  It is collaborating with the University sector to produce similar material aimed at students of architecture.

Supporting The Neighbourhood

The clay tile industry can make a significant contribution to local communities because:

• The employment it provides is long-term.
• The performance and continuity of a clay tile manufacturer’s operations encourages the establishment of links with local schools, colleges and other institutions to the benefit of all parties.
• It is important to clay tile manufacturers that their operations and impacts take into account the interests of the communities in which they are located, and are accepted by them.  Local liaison committees are an established means of achieving this end.

Supporting The Community

The Industry can help its local communities by providing amenity facilities as well as employment:

• Clay extraction has a temporary disruptive and adverse environmental impact.  However, subsequent restoration often adds value through the provision of leisure facilities and areas dedicated to wildlife and nature conservation.
• Restoration of clay pits can also provide land for agricultural and other productive uses.
• Waste disposal to landfill is the least desirable environmental option.  Nevertheless, the UK will continue to require some landfill facilities for the foreseeable future.  Clay is accepted geologically as the best receptor.  Restoration of clay quarries through landfill meets one of society’s basic needs.

Environmental Protection

The environmental impacts of the manufacturing process include clay extraction, energy consumption, atmospheric emission and noise.  These impacts are all heavily regulated and Table 1 lists the main areas.  The trade association, the British Ceramic Confederation is in regular discussions with the regulators to ensure realistic interpretation of legislative powers.  Although industry is committed to continual improvement and the majority of companies are operating environmental management schemes, to ISO 14001 or EMAS.  However, the benchmarks and acceptable practice are set by the regulators and meeting these should go a long way to demonstrate good environmental protection as part of the sustainability package.

Table 1 : Regulation of Environmental Impacts

Research undertaken by London Economics for the DETR in preparation for the introduction of the aggregates levy assessed the environmental impact of clay extraction as small compared with other minerals.  This is because:

• The volume and rate of extraction is low compared with other minerals.  Operations are often restricted to a limited number of weeks in any year.  The immediate impact and rate of change is therefore unpronounced.  Extraction is generally only economic where the ratio of unusable to usable material is relatively low.
• Companies have readily adopted practices ensuring compliance with the performance standards required to meet the stringent conditions demanded by planning permissions, such as those recommended in the BCC Environment Code on Extraction and Restoration.
• Responsible management of working sites ensures that they are an environmental asset, while old workings are restored to beneficial use, adding ecological value through projects designed to increase biodiversity.

Controlling Atmospheric Emissions

The main emissions resulting from the production process are carbon gases, hydrogen fluoride and particulates.  Continuous improvement in performance has been achieved through a constant drive towards increased energy efficiency.  The cost of energy and the need to reach targets prescribed in the industry’s climate change agreement are key influences in this respect.

CLIMATE CHANGE

The Climate Change Levy is a tax on energy used by industry, commerce, and public sector buildings and offices.

Energy intensive industries receive a rebate of 80% of the levy in exchange for agreeing and meeting challenging energy reduction targets.

The Clay Tile Industry has undertaken to achieve a reduction in specific energy consumption of just over 10% by 2010.  Clay tile manufacturers operating sites are included under the agreements.  Energy returns from individual companies are independently verified for the sector by CERAM.

Regulatory control includes process guidance notes prescribing limits of hydrogen fluoride and particulates emissions.

EMISSIONS

Permitted limits for atmospheric emissions by brick manufacturers are prescribed in process guidance note PG 3/2 : The Manufacture of Heavy Clay Goods and Refractory Goods.

The limits for existing plant are:

Hydrogen fluoride                                10mg/m3 at 18% oxygen

Particulates                                         100mg/m3 at 18% oxygen

In addition, for new or substantially changed plant, limits are prescribed for emissions of nitrogen oxides, hydrogen chloride and sulfur oxides.

Major capital investment in the technology to ensure compliance

Emissions of hydrogen fluoride from kiln exhausts can be substantially reduced by dry limestone absorption.

The industry has made significant investment in this area to improve environmental performance

Integrated Pollution Prevention And Control

The clay tile industry’s emissions are regulated by the Environment Agency or local authorities, under the Environmental Protection Act.

A new regime, implementing the EC Directive on Integrated Pollution Prevention and Control, is replacing the existing legislation. IPPC will take into account a wider range of environment impacts than previously.  Most installations in the clay tile industry are or will be subject to these controls.

Installations will also be required to demonstrate the application of Best Available Techniques to ensure a high level of environmental protection.  Guidelines, known as BREF notes, will be published by the European Commission and will provide the basis for national sectoral guidance on Best Available Techniques.  The UK clay tile Industry has contributed fully to the development of these guidelines including.

• The effective application within the industry of techniques to reduce water use and effluent levels reflected in the Envirowise publication, “Managing Water Use and Benchmarking in the Brick and Heavy Clay Sectors”.
• The range of guidance and advisory notes on aspects of environmental management produced by other organisations in partnership with the industry.

Guidance On Environmental Management

Advice designed to assist clay tile manufacturers improve their environmental performance includes:

Guidance on Introducing and Environmental Management System for Ceramics (BCC 2001)

This publication provides a practical guide to the introduction of a basic environmental management system.  It identifies the key components of a system and illustrates their application with practical examples from the industry, and identifies sources of further support and training.

Managing Water Use and Benchmarking in the Brick and Heavy Clay Sectors (Envirowise 2001)

This guide provided benchmark data against which companies can compared their performance.  It includes practical tips and examples showing how to achieve cost savings by reducing waster use and effluent generation.

The guide covers all process stages and gives advice on reducing effluent through the recovery of materials for direct re-use.

Extraction & Restoration : An Environmental Code for the Heavy Clay Industry (BCC 1999)

This code assists and encourages companies in the heavy clay industry to adopt practices which will publicly demonstrate their commitment to high environmental standards.  The code deals with the extraction of clay from quarries and their subsequent restoration.

Reducing Fluoride Emissions in Brick Tile and Pipe Manufacture (Envirowise 1999)

This guide shows how to evaluate whether process optimisation techniques can be used to reduce fluoride emissions from brick, tile and pipe manufacture.  It sets out a method for assessing whether process optimisation or a scrubber is likely to be the best solution.  It shows how the former, if practical, can reduce waste and save money.

Natural Resources

The Clay Tile Industry has set out to make the exploitation of clay as efficient as possible by:

• Sourcing materials locally.  The majority of clay tile works have their clay stocks on site or within close proximity.
• Working in conjunction with other operators such as surface mining to use clays that are a by-product of their main activity.
• Minimising the waste of clay in the production process by recycling unfired clay.
• Researching the use of additives that will reduce the quantity of clay required, eg sawdust, glass cullet and sewage sludge.

The Sectoral Mass Balance study of the UK Ceramics industry published in 2004 as part of the Biffaward Programme on sustainable resource use commented on clay waste.  Overall it was considered that the UK ceramics sector which had a low waste/product ratio at some 2% but that was heavily skewed by Heavy Clay sector which is very resource efficient.  This is reflected in one of the Key Performance Indicators for the sector the Overall Raw Material Efficiency.  This indicator is defined by mass of products produced divided by mass of raw materials (including water) consumed and for the Heavy Clay sector this is given as 71% as compared with a weighted average for ceramics as a whole of 45%.  This is explained in the report as due to the degree of automation and the high yields in the sector.

What waste there is which does go to landfill is totally inert and is often used in road surfacing or is crushed and recycled in concrete productivity.

Recent trials in the use of glass cullet in bricks made from Etruria Marl, a common clay for making roofing tiles has shown that in an intermittent kiln some 21% saving in energy was possible at the 5% addition level.  Other benefits include reduced emissions of hydrogen fluoride and carbon dioxide and increased throughput.  This work, sponsored by the Waste Resource Action Programme is being extended to consider the use of waste cathode ray tube glass and into the clay roofing tile sector.

Drying and firing the clay consumes energy.  During recent years the industry has improved its energy efficiency through:

• Installing more efficient computer controlled kilns from which heat is recycled to be used in the drying process.
• Undertaking energy monitoring programmes.
• Advances in burner technology and the installation of variable speed motors to match energy consumption to the task in hand.
• Using alternative fuels such as landfill gas from clay pits for firing product and generating energy.

Distribution of the finished product is potentially an expensive operation which contributes to environmental pollution.  The industry has made efforts to reduce this pollution by:

• Preserving the availability of locally manufactured products, despite the rationalisation of production plant.
• Arranging transport to an industry-wide basis to reduce the number of empty return journeys.
• Improving the efficiency of the lorry fleet by replacement of old vehicles and careful monitoring of fuel consumption and tyre wear.

Economic Prosperity

The clay roof tile industry continues to take a greater market share of the roofing market and is in a good position to continue to do so.  Supplies of suitable raw material are abundant.  There are great changes taking place in the construction market especially in housing but whether the future is in more and more prefabricated dwellings, brown or green field development the industry is well able to supply the roof covering.  All of this will continue to give scope for investment and further development of the industry.

SUSTAINABLE BUILDINGS : CLAY TILES

The outline Code for Sustainable Buildings introduces a number of new concepts for example the introduction of the SAP concept to water performance and many of those do not have direct consequences for clay roofing tiles.  As part of the input data to any BREEAM or Ecohomes assessment will be the summary rating in the Green Guide to Specification.  In the case of pitched roofing consisting of clay tiles, battens, sarking felt on a timber roof structure with insulation between the rafters the summary rating is “A”, the highest possible. This is of course beneficial to the industry but does assume replacement after 60 years.  There are of course numerous cases where clay tiles have lasted much longer, a good example being the  University Hospital of North Staffordshire where four buildings The Old Physiotherapy Building, The Old Administration Building, both built in 1842, the A Block and the Chapel both built in 1866 are being stripped of their 150,000 clay tiles in order to replace the substructure but 94% of the tiles are capable of and are being re-used.  There will of course always be individual examples but there are sufficient numbers of them to warrant extending the period.

Energy Performance

Clay Roofing Tiles in themselves offer very little by way of thermal insulation which is provided by high grade insulants to form a warm or cold roof structure.  In either case advances insulation standards will be met by greater thickness of insulation or better insulants.  The important point from the consideration of the roof structure is that Robust Standard Details are likely to be relevant with minimal revision.

Adaptability

As part of the sustainability package there is an element of adaptability of buildings to accommodate in particular growing families.  The room in the roof concept is already acknowledged as a low cost way of building in such adaptability and the additional material used in attic roof trusses is related to greater usable space and hence does not attract a penalty.

Standards

The Clay Roofing Tile manufacturers have through the Clay Roofing Tile Council and CERAM provided considerable input to the British Standards Institution and more recently the Committee for European Standardisation to ensure that product are fit for purpose.  Europe wide standards have now been established covering Definitions and Specifications based upon performance requirements together with the supporting test methods for flexural strength, impermeability, frost resistance and geometric characteristics.

Maintenance of Performance

CERAM has for four years been measuring the colour change of roofing tiles that have been exposed horizontally to atmospheric conditions on the flat roof of the laboratory.

In general after four years exposure, when compared with the original colour values determined at the start of the programme the clay tiles have lightened to an extent that is measurable, but not detectable to the human eye.

The clay tiles have moved slightly towards the red and blue end of the measurement spectrum which really complements the general and surface body colour of the tiles.

These interim observations are based upon aggregated changes measured on a large number of tiles and although individual tiles have changed colour at different rates the overall conclusion is that in general clay tiles mature attractively over time.

Re-Use and/or Recycling

Clay roofing tiles do have potential for re-use as described in relation to the University Hospital of North Staffordshire.  However, a roof is the most extremely exposed part of a building and freezing and thawing when saturated is the environmental action that can eventually cause tiles to fail.  Although the test methods available have been developed for new tiles they are a reliable guide. It is advisable to get an independent laboratory to test tiles to be re-used especially if there is a possibility of the application being in an area of harsher weather conditions or lower roof pitches than those where they have previously been used.

Future Proofing (Climate Change)

Future Proofing is a fairly new expression but the definition seems to be ensuring that products can withstand greater extremes of heat and cold than was likely to occur hither to and also greater extremes of wind.  As far as clay tiles are concerned greater extremes of heat are unlikely to be a problem as they have been fired at in excess of 1000oC and any changes at the 30oC, 40oC or 50oC level are unlikely to cause problems.  Similarly extreme cold is unlikely to cause a problem.  The freeze thaw testing that is undertaken in the laboratory on tiles that have been artificially saturated subjects them to an air temperature of -15oC which gives a surface temperature of about -8oC.  It is not anticipated that lower values would cause problems.

In terms of extremes of wind for a typical clay plain tile with minimum nail fixings (every fifth course) calculations show that with no unusual features in the calculations tiles in the general area of the roof at 40o pitch can withstand basic wind speeds that occur as for North as Preston and Leeds, in central Scotland, Central Ireland and most of Wales.  If for example the basic wind speed in London rose by 20% (from 20m/s to 24m/s) minimum nailing would be satisfactory for this particular roof.  If on the other hand wind speeds rose to 30m/s ie. the basic speed in the Shetland Isles, roofs would need to be renailed and for this particular case minimum nailing would need to be replaced by every second course being nailed.  Clearly this is one particular example but the point is that if the trend is towards more extreme winds clay roof tiles can be prepared to resist quite a large increase in wind by additional nailing.

CONCLUSION

Overall when one looks at the strides made by the industry in developing a Sustainable – manufacturing policy, together with the Green Guide ‘A’ rating achieved by clay tiles and the development of a Code for Sustainability, it is clear that clay roofing tiles are one of the more sustainable building products.  This is no surprise given their long history of use, fitness for purpose and ongoing popularity.  Sustainability is all about actions which do not inhibit the ability of future generations to act.  The longstanding contribution made to our roofscape by clay roofing tiles is a clear sign of sustainable decisions made by our forebears.