Water Penetration Mystery

[Nigel Watts]

Last weekend's storms resulted in water penetration through the roof in two parts of my house, both in areas reroofed within the last few years.

The house is an 1840 brick semi, four storeys high with a low pitched slate roof. The party wall carrying the chimney stacks rises above the roofline for the whole depth of the house, is rendered and capped.

A pint or two of water came through a small wire hole in the ceiling of a top floor bedroom adjacent to the party wall. When I went into the attic to see where it was coming from I noticed that water was running down the face of the brick party wall in a number of places.

I am rather mystified by this because only three or four years ago I had the roof recovered - new Welsh slate and new lead flashings at the junction with the party wall. Are the flashings faultly perhaps, or could the water be penetrating from the chimneys?

The other mystery is water penetration through the roof of my new lean-to extension. This has a continuous greenhouse-style rooflight the length of the lean-to. Above and below it the sloping roof is covered in lead. In stormy weather there is usually some water pentration in one section, at the upper edge of the rooflight. Could water be getting under the flashing and travelling uphill for a bit before getting in?

Any ideas?

Thanks

 

[thiambal]

I have exactly the same design of main roof and party wall rising above the roof line. I also have exactly the same leak problem.

I have been told by a number of tradesmen that this design of roof is a bit of a bugger to keep water tight and I notice that some houses on the street have lowered the party wall to below roof height and tiles across.

If you come up with a cause and more importantly a solution I would be very interested to know.

 

[Bus Godden]

Anything sticking up out of a roof deflects winds, creating eddies, gusts and venturi type turbulences in narrowed down spaces and defiles:

It sounds like a case of inadequate weather laps at the soakers or/and poor handiwork – if the pitch is sufficient then it should be entirely possible to weatherproof roof abutments perfectly well enough, in the majority of situations.

As for the lean-to, the same criteria could also apply, but check out the likelihood of capillary attraction and wind assisted creep on shallow pitches where there are close laid, tight, even surfaced materials (a judiciously dabbed line of mastic under leadwork can often cure many an ill!).

However, as you will all probably realise, making any kind of diagnosis from the comfort of ones desk is not without risk – experienced inspection should tell though.

 

[Lime]

I agree with Bus Godden that is is almost certainly "inadequate weather laps at the soakers or/and poor handiwork" assuming soakers are fitted. Often they are not.
Unfortunately much of the important part of lead work is hidden under tiles or other lead so cannot be seen or checked up on without a physical examination.
Under the lead flashing and under each roof tile should be a lead soaker that seals the underside of the tile against the brickwork.
The soaker prevents water being blown under the flashing from entering the building. These are often missing as builders know that it cannot be seen and any water getting in is rarely noticed. Instead they bring the lead over the tiles as a form of cover flashing.
If the soakers are properly fitted and the flashing suitably stepped, turned in and wedged it is almost impossible for any water to get in.
However in really exposed areas it is possible to fit cover flashing as well.
Thus the tiles have lead soakers underneath them, lead over the top of them and both the soakers and cover lead running up the brick work covered by the normal stepped flashing.

Here is a link to a previous thread in which I posted some pictures of flashing and soakers.

http://periodpropertyshop.co.uk/phpBB2/viewtopic.php?t=6387&start=0

Could water be getting under the flashing and travelling uphill for a bit before getting in?

In this situation it would be common for water to collect over the top the protruding window and with wind, capillary action and inadequate lapping water will enter.

 

[middi]

If the tiles have had lead soakers fitted and a lead flushing over the top of these, it is more or less an impossability for the roof to leak.

You probably find that they made a c**k up by design or by default.

Side wall tiles always will need soakers plus flushing otherwise there is no guaranty that it is going to be storm proof.

I would have a good look first with a torch from within the roof cavity to see if any soakers have been displaced, if you can get to it.

 

[Nigel Watts]

Thanks

Soakers and Flashings... all a bit technical but I will try to do some homework to find out more.

From what I can see from ground level (which is some distance away, the house being quite tall) the leadwork comes down the wall for a few inches then disappears under the slates. On the inside nothing much can be seen because the slates etc are the other side of the paper-like membrane which was laid over the rafters before the slates were applied.