Commonly found on older tenement roofs, particularly steeply pitched mansard roofs, and above bay and oriel windows. Lead has a long lifespan, sometimes over 100 years, so it is value for money. If you live in a listed building or in a conservation area, you may be required to replace your roof with lead rather than other materials.
Lead is commonly used for flat roofs because of its long lifespan and ability to be formed to fit many positions. However, lead must be laid and formed correctly to achieve this long lifespan.
Correctly laid lead roof. Note the height of steps between bays, the rolled joints, and adequate overlaps. Image courtesy of Greyfriars Roofing.
Problems
- look out for buckling or cracking of the lead, which is often caused by inadequate movement joints and can lead to leaks (and rot)
- look out for corrosion of the lead caused by lack of ventilation underneath or acid run-off from algae
- patch repairs suggest that lead cracking is a problem
- theft – consider replacing lead with an alternative material (note this will require consent in listed buildings and conservation areas)
Temporary patch repairs to a cracked lead roof. Note that the step between the two sections is too low and there is inadequate lapping at the joints.
Repairing a lead roof
Patching with other materials (felt, flashband etc.) can prevent further damage to your property and buy you time to organise proper repairs. However, don’t expect them to last very long.
A skilled worker may be able to weld a lead patch onto a roof that is otherwise in generally good condition.
Defective lead roof on bay window. Inadequate laps and overworked lead.
Correctly made lead roof on bay window
Replacing a lead roof
Cracked lead roofs will most likely need to be replaced.
- lead should be laid in bays (sections) with joints between the bays formed over a wooden roll – thicker lead is used on longer bays
- joints along the length should be stepped to prevent rain seeping up through capillary action
- lead is normally laid over a layer of building paper or geotextile membrane to allow it to slide over the sarking boards below as it moves with heat
- sarking should be laid with a small gap between each board to allow ventilation of the underside of the lead
- in some circumstances, it may be necessary to change the original detailing of the lead to ensure that expansion is coped with
Professional help recommended?
If the flat roof is covering a large part of your building and needs major repair or replacement, get a professional survey before proceeding as it may be possible to carry out other repairs at the same time.
Who pays?
Roof repairs are normally a common responsibility.
Further information
