Lead flashing - maximum length?

[Great_scot_selfbuild]

What is the maximum length of lead flashing in a single length I should use? I have some long windows and have read about allowing for expansion/contraction of lead, but want to hear from experience in this group as to what you would do?

 

window lengths:

1900mm

2500mm

4700mm

 

TIA

[Roger440]

1 to 1.2m seems to be the rule of thumb for valleys.

 

My valley had been done in a 3.5 m single length. It had crinkled up and split on the south west elevation

[JpManning]

For flashings the usual guidance is no single piece longer than about 1.5m, whether it's Code 4 or Code 5. Lead moves a fair bit with temperature, and if a long length is held at the ends it can't slide, so it ripples, fatigues and eventually cracks, which sounds like what happened to Roger's valley.

 

So for your windows I'd split them roughly like this:

 

1900mm: two pieces of about 1m each

2500mm: two pieces of about 1.25m

4700mm: four pieces of around 1.2m

 

Lap each joint by at least 100mm, and go to 150mm if the elevation is exposed or the pitch is shallow. Fix each piece so it can still move: wedge or clip it into the chase at intervals rather than nailing it solid along the length, and use copper or stainless clips on the free edge if it's catching the wind. Seal the chase with lead sealant rather than mortar.

 

Also worth patinating the lead once it's fixed, especially on light coloured walls or sills, as fresh lead run off can stain badly in the first few months.

[BadgerBodger]

Does it depend on Code? 
 

I did my code 4 lead step flashing in 1m lengths with 150mm overlap. There is a diagram in building regs if I recall showing minimum waterline  (min 65mm) etc. 

 

Chased into bed but still needs pointing. One of those jobs I’ll get round to one day…

 

Patination oil to both sides before fitting (seemed easier). 

 

Don’t recall seeing anything in regs for horizontal but doesn’t mean there won’t be one. Also not sure I’d expect it being any different for horizontal lengths (only 100mm permitted for pitched roof would probably revert to 150?) 

 

[Russell griffiths]

Get a copy of the Calder lead guide, very useful booklet. 
probably available online. 

[MPx]

Just had an excellent roofer do our slates and lead.  Its all in the "code".  Flashing is typically thin stuff code3(?) and ours was done with multi overlapping very short sections <400mm.  The valley is much larger and required code 7 to do it in 4 steps of circa 2m each - code 6 or 5 would have required more steps with the inevitable consequence of getting very wide at the high point.