Lead linings are commonly found in the valleys between pitched roofs and behind masonry parapets.
Defects here frequently seep quietly for months or years, providing the ideal conditions for dry rot, wet rot, insect infestations and other forms of decay. The correct use of lead is crucial to their success, and if correctly detailed and installed, these linings can last for centuries.
Failures caused by oversized gutters commonly present themselves initially as a ridge across the base of the gutter before a fatigue crack actually appears. A similar effect is caused by over fixing a correctly sized sheet.
Gutter failures can be the result of any of the following common causes.
Gutter bays should be fixed at the head, into the rebate of the step. If the fall exceeds 3° additional fixings will also be required at the base of the drip. However, if the fixings are taken beyond this point, then even a correctly sized bay will ultimately fail, with fatigue cracks appearing across the base of the gutter.
If the pitched roof covering is stone slate, such as York stone, then the weight of the stone on the lead can act in the same way as mechanical fixings down the length of the bay, with much the same effect as the above Over-fixing.
Run-off from lichen and moss
It is advised that any roof or gutter detail should have sacrificial flashing installed to catch the run-off from a slate or tiled roof that has a covering of lichen or moss, as it is mildly acidic and corrodes the lead at the point of contact. The flashing in this case would be held by clips allowing for easy replacements. The other option of course, is to have your roof cleaned and stripped of moss or lichen.