Bay window roof

After double-gazing it, my bay window roof has started to leak. Installers have been round and suggested that the roof failed some time ago and the water has just been percolating down through the woodwork in the past, and cracks in the paintwork caused by the installers have allowed the water to escape in a more noticeable place. This is reasonable; the windows are under big stone lintels that stick out quite a way and I see no badly fitted joints where water could get in. The leak is very slow- when the rain and wind are just right, you get perhaps a drop a minute.
Installers recommend getting someone in to tar the roof in a few months time. However, the roof was originally lead and there's a black coating, possibly of tar, that is worn off in places revealing the lead beneath. Neighbour re-leaded his bay some years ago because he didn't want to do a quick bodge that would start leaking again. Wife wants the cheapest possible fix. Hence my problem. Is recoating with tar (or one of these "10 year waterproofing paints") a viable option or is it a quick bodge that will give endless hassle?
Is re-leading never going to pay for itself in terms of how many 10 year re-applications of gunk it will save us?
-- Dr. Craig Graham, Software Engineer Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk /
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Do the job properly! How many ruined decorations or rotten roof timbers can you afford to replace? It might even be possible to solder a patch on the old lead - this used to be the established way of repairing leaks in lead roofing until all these gunges came on the market, making it easy for bodgers.
What also concerns me is that DG fitters usually have no idea about how to support bay window structures. Are you absolutely sure the leak has not been caused by structural movement resulting from their activities? It is an extremely common problem.
Peter
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Pictures and a general description of how they did the job would be the best bet here. Lead does fail. It warms up and expands in the summer but does not contract back the same way. In effect it flows. The top gets to be quite brittle and easily damaged.
I believe the glaziers should have propped the roof with an accrow inside the house. We can't say though from what we know here.
--
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Michael McNeil wrote:

Quick+dirty photo upload at http://www.blksheep.demon.co.uk/baywindow /
I don't think it's likely the installers could have caused the leak. The windows don't appear to be structural. The arrangement is three windows, a large middle one and two side ones, in a frame of foot thick stone. There are stone columns between the windows and stone lintels above.
The bay window roof is just below a bedroom window and there is visible paint damage that looks like a ladder has been there. The window cleaner's ladder may have been resting on that section and slipped, or it could just be cumulative damage. I guess window cleaners simply stand on the bay roof to clean the window which may not be so good. Interestingly, the window cleaner hasn't been for a very long time now- wonder if he knew something. I think the window cleaner putting the ladder up and standing on the bay to clean the bedroom window is more likely than the installers causing the damage. I don't think the installers even had a ladder. In addition, the bottom of the bay has always had a bit of a damp problem even though it's supposedly got a chemical damp proof thing (but no documentation- just the holes). This tallies with the installers suggesting a long term leak tracking down inside the old frame- plenty of space in the old sash boxes etc for water to get down undetected and percolate through the wall at the base.
Given the black gunk it seems the lead failed some years ago and the previous owners bodged it. The gunk is suprisingly uneven; one of the photos shows quite a thickness of pitted gunk in one area and bare lead in others.
--
Dr. Craig Graham, Software Engineer
Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk /
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Craig Graham wrote

No, you're right, they haven't.

(snip)
The lead is past its sell-by date Craig. It gradually wears thinner over the years due to acidic rain etc and also often corrodes on the underside due to condensation. There are areas in the photos where it is definitely pitted and perished. It looks like it is probably original from when the house was built, so it has earned its keep. The window cleaner may have damaged it, but you can't really blame him if the lead is so thin and maybe the boarding underneath has gone soft. I would guess it has been leaking on and off for a good few years, hence the black gunge. It's overdue for replacement.
You owe it to your house to reroof this little bay properly, using new lead. A small area like this will not cost very much different to felt or fibreglass or any other inappropriate muck and will look much more in keeping with the house. Reroofing will also give you the opportunity of replacing the boarding with plywood, and also putting some insulation in the roof.
It's quite a simple DIY job, and very satisfying if done properly, but as always you must use the correct tools and materials. You won't need to do any welding or soldering, just cold beating with a proper leadworking bosser available from any builders merchants. The decking should be replaced with 18mm WBP ply securely screwed down to the joists with brass screws, and ideally you should grab the chance to provide some ventilation openings if possible. To avoid splitting due to thermal expansion/contraction, the lead needs to be fairly thick - at least BS Code 5. The timber roll should be preserved softwood and the clout nails of copper or possibly aluminium.
Instructions and details how to do the job are available from The Lead Sheet Association http://www.leadsheetassociation.org.uk /
If you feel you're really not up to it you can find specialist leadworking contractors here: http://www.lca.gb.com/main.html
You'll be proud of it when it's finished!
Good luck Peter
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Peter Taylor wrote:

. .
Thanks for the responses. I think this latest one helped persuade the wife that it would be better to do the job properly rather than re-apply the previous owner's gunk.
I don't feel it's something I can do myself, though. If the living room was due for redecorating and it didn't matter if my attempt caused worse leaks then I might, but the present leak is right at the edge and is only affecting the window frame.
Hopefully by summer, when it's dryer, I'll have recovered from the cost of the window and can get someone in to do it properly :/
--
Dr. Craig Graham, Software Engineer
Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk /
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Lead doesn't usually fail if correctly done and not subsequently damaged - unlikely I'd have thought on a bay window roof, although it's suspicious that your neighbour had to have his replaced.

It's quite possible to DIY lead - and very satisfying to work with. The cheaper alternative is zinc, and again can be a DIY job for those with basic metal working skills.
--
*If your feet smell and your nose runs, you're built upside down.

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Hi,
Best way to find a leak is to go round the roof with a hosepipe, hose a section at a time and narrow it down from there.
Given the cost of bitumen and the cost of re-leading it's probably worth trying the bitumen first, no point re-leading to fix a pinhole leak.
A pressure washer on reduced pressure might be useful for finding the leak and removing any loose bitumen before recoating.
cheers, Pete.
On Mon, 2 Feb 2004 17:52:00 -0000, "Craig Graham"

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