Lead roof valley expansion techniques?

[michael]

I am currently having my roof recovered with real slate tiles and this will also involve the rebuilding (recovering) of an adjacent narrow roof valley in lead. The existing valley which collects rainwater from the pitched roof (the one being re-slated) is about 12 or 13 meters long by about a foot (30cm ) wide and appears to have been built from either copper or Zink (too grubby to tell) and has obviously had some patchwork repairs in the past. This original valley was also built practically flat with no apparent means for expansion consequently small cracks and bulges are evident which may be the reason for some of the past repairs.
My roofer had originally proposed rebuilding this valley in lead with a serious of steps falling towards the low point however having calculated back to the high point he has advised that the steps would lift the valley too high to the extent that it would override a very low sitting cast iron roof light in the adjacent slated pitched roof. This by the way is an existing roof light which cannot be moved due to the light well below it. He has therefore suggested taking up the expansion of the lead with a serious of purpose made rubber joints instead of steps, which he advises are commonly used by roof lead workers these days. Doesn’t sound like a very authentic solution for an 1880 building to me? Can anybody advise on this?

 

[chuckey]

There is a spec. on lead flashing that the pieces should not be more then 1 1/2 m long. What I would do is to make each piece the 1 1/2m long X what ever width they are. using a piece of hard board as a former, fold over each end of the lead strips by about 2" and tighten down to the hard board, and from the short end mark a line 1 " away across the width. Do the same at the other end, making sure that the "hooks" are facing in opposite ways. The bottom strip is fixed first, with its one hook facing upwards. The second strip is put on top of the first and slid upwards until its bottom hook is engaged with the first leads hook and its end is aligned with the 1" mark and fixed. This process is repeated all the way up the slope. Each joint is just tapped down for neatness. This should allow each piece of lead to expand and contract by up to 1/2 " in length with the overlap should stop any capillary action. The active area of a 1 1/2 m strip will be only 1.425m. So get your length, if its 12m its s*d, because you will need 8 lengths, so you might as well use up the excess in increased overlaps/hooks.
Frank

 

[Gervase]

Chuckey's right - the standard guidance on lead is no more than 1.5 metre lengths, but hook joints should allow for expansion. The only nails should be at the top of the sheets, and rubber or silicone mastic (other than to seal a mortar joint) is a no-no.
If you Google Calder, the lead millers, you'll find a 24-page PDF guide to leadwork on their site which is extremely useful.

 

[Lime]

I had roofers lead part of my flat roof on my new kitchen.
They used little folded overlaps to join the sheets of lead.
At the time I said I would have preferred rolls but I was overruled by the builder.
Within 2 months I had them rip it all off again because the folds were letting in water and they had to use rolls as I had originally argued for.
Water travels uphill quite readily when in a confined space (like between two sheets of lead) through capillary action.

My feeling with this small valley is that they didn't use lead for a reason.
Copper has nearly half the coefficient of thermal expansion of lead so doesn't expand so much.
Also copper is ductile while lead is not and lead will split and crack readily.
Although michael gives no detail about the step heights perhaps it would be possible to use copper with fewer, lower steps to do the job properly?

 

[michael]

Thanks every body. Really useful information, I’ll have a word with my roofer and look at using an alternative to lead to try and reduce the number of expansion joints and height of the steps. I was told however that in this relatively flat valley where there is the possibility of torrents of water coming off the adjacent pitch roof i.e. in a storm, that water could find its way in through the joints. i.e. that the jointing system should really only be used where the lead /copper roof itself has a significant pitch to allow the water to run off. Is this correct? In my case the valley in extreme downpours could for a time be submerged in water.

 

[chuckey]

As a back up feature, line your woodwork with a (one) piece of 60 cm wide damp course plastic(for walls not floors- it comes in long rolls). Stick it down with silicon goo. Lead then just protects it from the sun (and rain :lol: )
Frank

 

[michael]

Conclusion: I spoke to the “Lead Sheet Association” very helpful. They advised that these purpose made expansion joints are quite good, they’re made of neoprene. The draw back is they have a life expectancy of about 18 – 20 years and a guarantee (if available) of only 10 years. Lead installed with the traditional stepping technique on the other hand has a life expectancy of 60 -100 years. Advice given was to use neoprene expansion joints only where I have to. So run the valley in steps as far as I can until I’ve reached the maximum height available then run the remainder at minimum fall (1:84) using the expansion joints. By doing this, I will only have to keep an eye on two neoprene expansion joints 10 years down the line rather than a potential five or six. I was also advised to use the thickest lead I can to extend the distance between steps :
(Code 4 = 1.5 m, with 50mm step), (Code 5 = 2.0 m with 50mm step), (Code 8 = 3.0m with 60mm step). I cant afford the crane to lift the code 8 so I’m going to plug for code 5.

 

[Penners]

I was overruled by the builder.

That doesn't sound like you, Lime! But it is an object lesson in not taking it for granted that your builder is an expert in everything.