We have no Roman roofs surviving in this country, so we drew on archaeological evidence. The roof frame was customarily of timber drawn from reasonably close to the building site, from woods which would have been managed to provide small and large timber and this meant planning ahead, as big trees do not grow quickly. In Roman times, southern England was not covered in wild untamed forest and it would have looked more like today's countryside.
At the Butser Roman Villa, the roof type uses strong timber supports in the form of 'trusses', based on evidence from excavations in London. Each truss is like a capital letter 'A' but with a central post and cross-bracing to give extra strength and stability. These trusses are tied together with horizontal timbers and boarded.
The Romans' construction of roofs was crude. Joints were made by chopping the timbers flat and simply nailing the one to the other. Roman roofs are utilitarian - beauty and civilisation are expressed in other ways.
Nails are the great disposable item of Roman culture. They are discarded with no apparent attempt to recycle them. Considering the labour that had gone into the production of the iron for that nail and then its hand forging (at say at least two or three minutes per nail), which represents, in total, a large effort, this is perhaps surprising.
We perforce used a large crane to put the roof timbers up in a mere ten days. While it would have been more difficult for the Romans to lift the timbers, they would have had plenty of people to help, although it would have taken longer.
Ideally the main roof of the villa would have been covered in grey stone Purbeck slate from Dorset, just as appeared to be the case from the Sparsholt records, but as they are so expensive a modern substitute material was used. The original slates were cut to a diamond pattern, with one nail hole for securing to the roof. It is thought that they were laid in an overlapping pattern.
Other types of roofing material are known, such as tiles. The 'classic' form of Roman roof is of flat tiles with two sides raised ( tegulae) which are laid flat and overlapping each other (like fish scales). The gaps where the flanges butt together are then covered by half round tiles (imbrices). This was the indicated covering for the corridor.
Choosing the slope of the roof caused problems.
In this country, because it rains heavily, the slope of a roof needs to be great enough for the water to flow off quickly and not leak in. However, steeper slopes need more wood for the roof and the roofing material must be kept in place, either under its own weight or by nailing or pegging. Thatch is a good roofing material but only if it is set at an angle of 50 degrees to throw the rain down the stalks, to minimise rotting.
Stone slates nailed to boards can take a slope somewhere between thatch and tiles. In the Mediterranean area, tile roofs are usually at about 20 to 25 degrees. Experiments suggest that on boarded roofs the angle can be increased to 30 degrees, if the tiles are mortared together. Increasing the angle of the slope also means that the number of tiles needed to cover the roof increases significantly.
In deciding on the slope of the main roof, we considered British examples from the collapsed ends of Roman buildings. One showed a roof slope of about. 47.5 degrees with stone slates as the roofing material. This steep slope could exist simply because the building was originally thatched and had been subsequently re-roofed. Another example indicated a roof slope of only 22 degrees.
With the Butser Villa, we finally compromised with 32 degrees for the main slated roof and 26 degrees for the tiled corridor, partly for economy and partly because of the influence of local Planning Controls.
Created 15 November 2003 - Updated 15 November 2003