Here is a worrying case: a lead flat roof on a Listed building that was renewed less than 20 years ago. Superficially it looks like a good job but one or two tell-tale leaks tell another story.
Investigation of the lead reveals that it is, in places, paper thin. What is going on? The leadwork is subject to an insidious form of corrosion which results from condensation on the underside and leaves the lead looking perfect until it starts to fail.
At the time that this work was done we, as a practice, were very well aware of this hazard and of the steps required to be taken to avoid it and we knew very well to take a holistic view before deciding on the specification and make up of roof coverings.
Currently we are renewing two fibreglass roofs on a listed castle putting them back to lead. The client wishes to have a contemporary standard of insulation but this gives rise to a real risk of condensation. To achieve both we have been very systematic in the provision of ventilation below the leadwork.
Be sure to use a Chartered Building Surveyor experienced in the care and conservation of old buildings to specify roofing work.
Use a Chartered Building Surveyor experienced in the care and conservation of old buildings, not a roofer or a valuer, to inspect and report on roofs.
By: David Gibbon MRICS MBEng
RICS Conservation Accredited Building Surveyor