Roof Coverings

Slate roofing The main sources for roofing slates in Britain are Cumbria, Cornwall and North Lancashire in England, and Bangor, Portmadoc and Caernarvon in Wales. There are no longer large scale quarries in Scotland; therefore the main source of Scottish slates is from demolition for use second hand. On the British market there are also roofing slates from European countries such as Spain and Portugal. Roofing slates are said by the tonne or by the thousand depending upon the source. 

British Standard BS680 Part 1:1944 (imperial) and Part 2:1971 (metric) details geological formations of true slate rock from which roofing slates can be quarried, together with characteristics, grade tests and sizes. The labour outputs given here are for standard site slates in accordance with BS 680 Part 2 Table 1 'Standard lengths and widths of slates'. Sizes of randoms and peggies can be obtained from Table 2 'Range of lengths for randoms and peggies'. The labour outputs in Table 9.1 are based on a squad of two slaters and one labourer, and allow for carrying and fixing in position. Unloading, holing and dressing of slates are highlighted as required in the examples, which follow.

The wastage on slates is taken as 2.5 per cent for sized and 5 per cent for unsized slates. Under the rules laid down in SM M7, roof and wall coverings are measured in square metres, and items are deemed to include underlay and battens. These items have therefore to be accounted for under the superficial items for slating and tiling where required. Tables 92 and 9.3 show expected slater outputs for a range of tasks. 

In the following examples, in order to calculate the cost per Int we have first to establish the coming capacity of one slate. To do this we have to calculate the gauge (fixing centres) of the slate and multiply by its width. 

For head nailed slates, the gauge= average length - (lap + 25 mm) 

                                                                              2 

For centre nailed slates, the gauge = average length - lap

                                                                             2

Gauge may also be defined as the length of slate visible. 

Roof and slate angles