Home > English Heritage Transactions volume 9: Stone Roofing > Excerpts
Sourcing new stone-slates and re-roofing the nave of Pitchford Church, Shropshire Chris Wood, Terry Hughes.
The roof construction was investigated by Terry Hughes on the 1st and 2nd of December 1998 (Hughes 1999). The investigation covered an area of about two metres width from eaves to ridge on both sides of the roof and was carried out from a scaffold at three levels: at the eaves and at approximately 6' (1.8m) and 12' (3.6m) above (Figs 20 and 21). This allowed all areas of the roof to be reached for careful dismantling by hand. The main area of the scaffold at the eaves was larger than normally required for roofing as it would later be used for the main repair work when adequate space would be needed to sort and redress the existing slates. Some of these were over 600 mm (24") square, the largest weighing up to a 1 cwt (50.8 kg). The whole area under investigation was covered and weather-proofed with scaffold sheeting. To ensure adequate lighting for photography (plastic sheeting gives photographs a green cast) and late working, two portable tripod mounted floodlights were used.
The plant growth (lichens, mosses and ferns) was so thick over most of the roof that the vertical and bottom edges of the slates were often obscured (Figure 22). The stone slates were therefore cleaned off with a scraper and stiff hand brush prior to progressive stripping from the ridge. As each course was removed the exposed area below was photographed using 400 ASA monochrome and colour negative film. The photographs were taken from a point perpendicular to the slating wherever the scaffold permitted and included a scale rule with 50 mm (2") divisions (Fig 23) and a number 40 mm (1¾") tall for each course. Groups of slates were also photographed laid out on the scaffold to record their shape, degree of shouldering and the ratio of the length to the width. All these factors are important in preventing the penetration of rainwater. A description of features of each course were recorded into a dictaphone as work progressed. 
The slate lengths below their fixing holes, head laps and margins, the vertical dimension of the exposed area of the slate, were measured at each course (Figs 23 and 32), except where the courses had collapsed onto each other. In this situation only the slate length was meaningful.
On a roof of this type and especially because of its deteriorated condition, measurements of head laps and margins could not be precise. The margins varied considerably along each course. Also, the head lap was somewhat theoretical. It is a dimension by which the roof is set out rather than the precise head lap achieved which is affected by the shape of the slate’s top edge and the position of the fixing hole. The head lap achieved depends firstly on the position of the perpendicular joint in the course above in relation to the curve of the slate head (if it drops below the peg hole) and, secondly, on the position of the peg hole laterally in relation to the perpendicular joint. For these reasons it is not possible to work out any of the three measured dimensions from the other two.
In spite of these difficulties, with care and a large number of measurements, it was possible to draw conclusions about the construction of the roof, and the apparent intentions of the contractors.