Question 1

How long should lead flashing last?

Accepted Answer

Correctly specified and correctly sized, a very long time — a century is realistic on a well-detailed roof. Lead that fails in ten or fifteen years has almost always been laid in pieces that were too long, so thermal movement fatigued and split it. That is a workmanship failure, not a material one. Lead has been used at the awkward junctions of roofs for centuries because nothing else does the job as well. It can be dressed by hand into any shape, it is completely impervious, it does not degrade in sunlight, and it forms a protective patina that stops further corrosion. The catch is that it moves. Lead has a high coefficient of thermal expansion and it is soft, so a piece restrained at both ends and heated and cooled through the seasons will work-harden and eventually crack. That single fact explains the overwhelming majority of failed leadwork in this country. The rule in practice is that pieces are kept short and lapped rather than run continuously. For code 4 flashings that means lengths in the order of 1.5 metres, with a lap at each joint so the sheet can move. A long unbroken run looks tidier on the day and costs less in labour, and it splits — always across the middle, usually within ten to fifteen years. If your flashing was 'done properly' a decade ago and has cracked, this is nearly always why. Code — the thickness — is the other specification. Lead sheet is sold by code number, and the right one depends on the position: code 4 is a normal minimum for flashings and soakers, while back gutters, valleys and anything taking real water volume want code 5 or heavier. Undersized lead fatigues faster and tears at its fixings. Support matters too. Lead should sit on a sound, smooth substrate with no sharp arrises to cut into it, be fixed at the head and left free to move at the tail, and be held with compatible fixings — copper or stainless, never something that will set up a reaction. Lead dressed over a sharp edge thins at that point and fails there first. Where lead has localised damage, the repair worth having is lead-welded — a permanent, invisible fix. What is not a repair is flashing tape, mastic or bituminous paint over a split: those hold water against the lead, hide the crack, and make the eventual proper repair worse. Black bituminous paint over a junction is the traditional way to conceal failed lead, and it is the reason a lot of leaks are found late.

Question 2

Why has my lead flashing split?

Accepted Answer

Correctly specified and correctly sized, a very long time — a century is realistic on a well-detailed roof. Lead that fails in ten or fifteen years has almost always been laid in pieces that were too long, so thermal movement fatigued and split it. That is a workmanship failure, not a material one. Lead has been used at the awkward junctions of roofs for centuries because nothing else does the job as well. It can be dressed by hand into any shape, it is completely impervious, it does not degrade in sunlight, and it forms a protective patina that stops further corrosion. The catch is that it moves. Lead has a high coefficient of thermal expansion and it is soft, so a piece restrained at both ends and heated and cooled through the seasons will work-harden and eventually crack. That single fact explains the overwhelming majority of failed leadwork in this country. The rule in practice is that pieces are kept short and lapped rather than run continuously. For code 4 flashings that means lengths in the order of 1.5 metres, with a lap at each joint so the sheet can move. A long unbroken run looks tidier on the day and costs less in labour, and it splits — always across the middle, usually within ten to fifteen years. If your flashing was 'done properly' a decade ago and has cracked, this is nearly always why. Code — the thickness — is the other specification. Lead sheet is sold by code number, and the right one depends on the position: code 4 is a normal minimum for flashings and soakers, while back gutters, valleys and anything taking real water volume want code 5 or heavier. Undersized lead fatigues faster and tears at its fixings. Support matters too. Lead should sit on a sound, smooth substrate with no sharp arrises to cut into it, be fixed at the head and left free to move at the tail, and be held with compatible fixings — copper or stainless, never something that will set up a reaction. Lead dressed over a sharp edge thins at that point and fails there first. Where lead has localised damage, the repair worth having is lead-welded — a permanent, invisible fix. What is not a repair is flashing tape, mastic or bituminous paint over a split: those hold water against the lead, hide the crack, and make the eventual proper repair worse. Black bituminous paint over a junction is the traditional way to conceal failed lead, and it is the reason a lot of leaks are found late.

Question 3

Lead flashing life expectancy

Accepted Answer

Correctly specified and correctly sized, a very long time — a century is realistic on a well-detailed roof. Lead that fails in ten or fifteen years has almost always been laid in pieces that were too long, so thermal movement fatigued and split it. That is a workmanship failure, not a material one. Lead has been used at the awkward junctions of roofs for centuries because nothing else does the job as well. It can be dressed by hand into any shape, it is completely impervious, it does not degrade in sunlight, and it forms a protective patina that stops further corrosion. The catch is that it moves. Lead has a high coefficient of thermal expansion and it is soft, so a piece restrained at both ends and heated and cooled through the seasons will work-harden and eventually crack. That single fact explains the overwhelming majority of failed leadwork in this country. The rule in practice is that pieces are kept short and lapped rather than run continuously. For code 4 flashings that means lengths in the order of 1.5 metres, with a lap at each joint so the sheet can move. A long unbroken run looks tidier on the day and costs less in labour, and it splits — always across the middle, usually within ten to fifteen years. If your flashing was 'done properly' a decade ago and has cracked, this is nearly always why. Code — the thickness — is the other specification. Lead sheet is sold by code number, and the right one depends on the position: code 4 is a normal minimum for flashings and soakers, while back gutters, valleys and anything taking real water volume want code 5 or heavier. Undersized lead fatigues faster and tears at its fixings. Support matters too. Lead should sit on a sound, smooth substrate with no sharp arrises to cut into it, be fixed at the head and left free to move at the tail, and be held with compatible fixings — copper or stainless, never something that will set up a reaction. Lead dressed over a sharp edge thins at that point and fails there first. Where lead has localised damage, the repair worth having is lead-welded — a permanent, invisible fix. What is not a repair is flashing tape, mastic or bituminous paint over a split: those hold water against the lead, hide the crack, and make the eventual proper repair worse. Black bituminous paint over a junction is the traditional way to conceal failed lead, and it is the reason a lot of leaks are found late.

Question 4

Can lead flashing be repaired?

Accepted Answer

Correctly specified and correctly sized, a very long time — a century is realistic on a well-detailed roof. Lead that fails in ten or fifteen years has almost always been laid in pieces that were too long, so thermal movement fatigued and split it. That is a workmanship failure, not a material one. Lead has been used at the awkward junctions of roofs for centuries because nothing else does the job as well. It can be dressed by hand into any shape, it is completely impervious, it does not degrade in sunlight, and it forms a protective patina that stops further corrosion. The catch is that it moves. Lead has a high coefficient of thermal expansion and it is soft, so a piece restrained at both ends and heated and cooled through the seasons will work-harden and eventually crack. That single fact explains the overwhelming majority of failed leadwork in this country. The rule in practice is that pieces are kept short and lapped rather than run continuously. For code 4 flashings that means lengths in the order of 1.5 metres, with a lap at each joint so the sheet can move. A long unbroken run looks tidier on the day and costs less in labour, and it splits — always across the middle, usually within ten to fifteen years. If your flashing was 'done properly' a decade ago and has cracked, this is nearly always why. Code — the thickness — is the other specification. Lead sheet is sold by code number, and the right one depends on the position: code 4 is a normal minimum for flashings and soakers, while back gutters, valleys and anything taking real water volume want code 5 or heavier. Undersized lead fatigues faster and tears at its fixings. Support matters too. Lead should sit on a sound, smooth substrate with no sharp arrises to cut into it, be fixed at the head and left free to move at the tail, and be held with compatible fixings — copper or stainless, never something that will set up a reaction. Lead dressed over a sharp edge thins at that point and fails there first. Where lead has localised damage, the repair worth having is lead-welded — a permanent, invisible fix. What is not a repair is flashing tape, mastic or bituminous paint over a split: those hold water against the lead, hide the crack, and make the eventual proper repair worse. Black bituminous paint over a junction is the traditional way to conceal failed lead, and it is the reason a lot of leaks are found late.

How long should lead flashing last?

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