Lead is a traditional building material that has been used for hundreds of years. Lead is a high quality material but it is not indestructible. It needs to be installed and importantly maintained correctly.
Lead is very long lasting, resistant to decay and soft enough to be squashed and pushed into difficult corners and around junctions to provide a waterproof seal in any situation. It also does a good job of keeping your roof free from moss and weeds. When rainwater runs off the lead material, it becomes very slightly toxic, not enough to be dangerous but just enough to stop plants growing on your roof.
On a recent inspection of a lead roof, I came across a failure that was not immediately obvious. Lead can weather and erode quickly in some circumstances but although over 120 years old, this lead was mostly in good condition. It hadn’t been altered during its life time. It was thick, heavy, high quality lead. There was no obvious impact damage. What was causing it to fail?
In spite of their reputation, you might be surprised to know that the Victorians buildings weren’t always constructed well. In this case, the failure was the result of a design flaw by the original builder and architect, in this instance, no less than the renowned Alexander Ross.
Like any metal, it expands and contracts a lot with heat, and roof materials get very hot in the sunshine and very cold at night. It is important that lead roofs and flashings are constructed in a way that can cope with the movement caused by these changes in temperature, otherwise the lead will split and tear, allowing water to enter the roof structure.
Building conservation expertise and experience are critical for not only identifying a problem like this, but also for developing an effective repair. Without the appropriate knowledge, a regular builder or surveyor might not understand the issue and recommend the wrong solution.
Attempt have been made at repairs and the roof has been patched at various times with bitumen paint, flash band and fibreglass. These are only temporary. They do not solve the underlying problem and failures will continue to happen. At some point a more comprehensive solution will be required, it is better to do this when the work can be planned and organised for the best cost, rather than in a rushed response to another sudden and unexpected failure. Urgent repairs are always the most expensive.
MAAC studio are accredited conservation architects and principal designers working with traditional buildings throughout Scotland.