Concern for the environment is a major influencing factor for the prospective homebuyers and builders. Whether or not they have any influence, buyers are concerned as much about preserving the landscape as they are about the materials used in building and demand natural, sustainable products. Clay tiles are considered by many planners and specifiers, as a sustainable product because of their durability, long term visual effect on the environment, and their properties as a renewable natural resource. These factors, along with the fact that they are being specified increasingly by planners and conservation officers to preserve the character of buildings and the architectural landscape, mean that clay continues to be one of the most desired roofing products. Recent evidence of the increase in the use of clay tiles is demonstrated by the fifty percent increase in the volume of clay tiles produced and sold per annum since 1995.
Code for Sustainable Homes
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.
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.
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.
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.
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.