Going Through the Roof
Article by Catherine James
The most common type of roofing material found in domestic dwellings in the UK is of a pitched construction. The pitch structure is formed in timber. Pitch roof covering can be of tile, slate, stone or thatch. The choice of roofing materials for domestic building has, throughout history, been determined primarily on availability of that particular material.
Clay plain tiles have been made in Britain since Roman times. During the Middle Ages the skills needed to mould and fire the clay into roofing tiles was lost. Roofing materials reverted back to thatch and wooden shingles. However this reversion to earlier materials was for a short period. By 1212 it was an Ordinance that new roofs in London were no longer to be made of thatch, and gave clay tiles as a suitable alternative roofing material.
Over the centuries clay tile roofing remained the best option of roofing material for domestic houses. As the product was handmade in local wood fired kilns with widely varying temperatures, the finish product varied greatly in size and quality throughout the counties of England. The method of production and size of tiles was put into the statute in 1477 by Edward IV’s, this went no where near the problem of standardizing kiln temperatures. This was beyond the technical knowledge of engineers of the fifteenth century.
The use of these localized roofing materials continued through the following centuries until the late Georgian period at which point the trend for tiled roofs changed to slate. This was as a result of the recent developments in quarrying which made available to the roofing industry excellent slates in a choice of various colours at affordable prices. Due to abundance of slate during this period, lower quality slate was also used for urban and cottage roofs. Indeed the use of slate as the main roofing material for domestic properties continued until the 1900′s.
Machine made roofing tiles began to be produced during the Victorian period. These roof tiles were used in cheap housing of the period. The Victorians saw these mass produced roofing materials as inferior to slate. This prejudice proved to be correct. Initial processes to produce the clay for roof tiles where poorly designed and implemented. During the early industrial manufacturing period, the grinding process of the clay frequently proved inadequate. When a clay body is inferiorly mixed together it lacks the uniformity of texture required for a good hard wearing tile. The grains of clay vary in size and air pockets are not fully removed from the whole. The end result being that when these clay tiles were subjected to frost they were highly susceptible to cracking and lamination.
The plain tiled roofs of quality houses in of the twentieth century tend as a rule to demonstrate good examples of the tillers art. The tiles will have been sourced from a reliable manufacturer removing the possibility of inferior roofing tiles. Chimney stacks and parapet walls will be lined with lead to eliminate leakage at joins. Most importantly good quality materials, together with professional tiling will be evident. In these properties, as a general rule, simple roof repair type maintenance is generally all that is needed.
Houses built during the late 19th, early 20th century that have not benefited from the professional tillers art, and to compound things, have been roofed with inferior clay roofing tiles. These roofs present the roof repair professional with more of a problem. If poor quality roofing tiles have been used it is usually the case that the tiles have also been laid in using a poor and now, fortunately outmoded technique were the roof tiles are laid out on feather-edged boarding. This feather edged boarding is nailed directly onto the rafters of the house.
In such a situation it is often better to remove all the roofing materials and re-roof the entire building a roof repair man can only do so much. When the roof tiles and the roofing construction and tiling technique combine together to make a rotten roof, roof repair and maintenance must move into re-roofing.
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