Lead is still invaluable as weather protection for many traditional British buildings. Even when not used as a roof covering, it can be present as a gutter or flashing, or a bridge at awkward junctions between walls and roofs.
Before cast iron became common, lead was also the main material for rainwater pipes and cisterns. Some magnificent dated and decorated samples of this survive.
Lead roofs and gutters are made by laying sheets of the metal onto timber boards. Jointing details allow the sheets to integrate, producing a weatherproof surface.
Lead sheets come in different weights, given code numbers. Code 7, for example, is used for larger sheets on historic roof repairs. The number indicates the lead is of a thickness to weigh 7lb per square foot.
A thinner code 4 or 5 might be used for flashings.
The weight of the lead has health and safety implications, too. On a roof, lead sheets can only be effectively manouevred by hand. David Lodge of Essex builders Lodge and Sons says that his firm must now have extra manpower on site to lift lead sheet into place.
There is a long tradition of marking lead (officially or unofficially). Plaques are most likely to be found on country houses or churches with large areas of lead, but lesser buildings may still bear the historic graffiti of workers – most common are the outlines of hands and feet, often initialled and dated.
What to Watch Out For
Lead can survive on a roof for generations, but, as with all roof coverings, some deterioration eventually occurs, mostly at joints and junctions. Over time, with repeated warming and cooling, large sheets of lead have a tendency to ‘creep’ down a roof slope.
Occasionaly, lead deteriorates from below, not above. Chris Wood from the Building Conservation and Research team at English Heritage suggests that if no unusual decay has been encountered during repair, there should be no need to alter the constructional form and detail of an old lead roof. However, English Heritage is researching why lead sometimes corrodes on the underside. Weather changes when laid and changes to the inside of the building can be significant.
Condensation is at the heart of the problem, and various measures can be taken to protect newly-laid lead from this corrosive acidity, namely:
Patch repair is possible, but requires heat which has, in the past, lead to some disastrous house fires. The National Trust now has a stringent policy on lead burning.
Lead roofing has been used on some of the country’s best buildings, with an enviable record of performance and longevity. Accept no substitutes.
Contacts and Information:
* The Lead Sheet Association
(01892 822773) www.leadsheetassociation.org.uk
* Lead Roofs on Historic Buildings
(English Heritage advice notes – 020 7973 3000)
* SPAB Technical Advice
(020 7456 0916)