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Roofing

Porch lead flashing 70mm overlap

Anonymous user 01/09/2025 - 12.45 PM

I’ve just had some lead flashing re-done and fitted to my porch and I’m looking for a bit of advice. The overlap between the two sections of lead looks to be around 70mm. From what I’ve read in the Lead Sheet Association guidance and BS 6915:2001, overlaps should be at least 100mm to prevent water ingress. I’m wondering if 70mm is acceptable in practice (given this is only a porch and fairly sheltered) or if it should definitely be redone to meet best practice. I’d really appreciate the opinions of those with experience in roofing and leadwork. Thanks in advance!

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5 Answers

Treetop Roofing LTD

Rating: 5 out of 5
Tredegar
Hi always a minimum of 4 inches or 100mm
Answered2 September 2025
1

Gibson roofing

No reviews yet

Wirral
Its a minimum of 150mm 6 inches for any lead coverage. Anything less does not protect you from capillary action coursed by wind. Hope this helps
Answered29 August 2025
0

Bentham Builders

Rating: 5 out of 5
Willesden, London
While 70mm may hold up for a while on a sheltered porch, it isn’t considered best practice and could fail over time, especially in heavy rain or wind-driven conditions. For peace of mind and long-term performance, I’d advise having it redone with at least a 100mm overlap.
Answered1 September 2025
0

Arian Palushi

Rating: 5 out of 5
Walthamstow, London
According to the Lead Sheet Association and BS 6915, the minimum recommended overlap is 100 mm. At 70 mm you are under spec, which increases the risk of water tracking back in, especially in driving rain. While it may perform for a while on a small, sheltered porch, it isn’t technically correct and could shorten the life of the work. Best practice would be to redo it with at least a 100 mm lap so you’ve got a proper guarantee against leaks.” But some times depends on the circumstances even 70 mm overlap can do the job
Answered1 September 2025
0

Bloom Roofing Ltd

Rating: 5 out of 5
Borehamwood
Hi there, always a minimum of 100mm between sections to create a watertight seal
Answered1 September 2025
0