Chapter 1: Why is there a damp patch below the valley on our Victorian house in Pangbourne?
What we find
A Victorian roof with a projecting bay, a rear wing or a side gable has valleys, and each valley is a lead-lined channel taking the water of two slopes. Lead sheet laid more than a century ago can crack along its folds, thin with the weather or tear where it was nailed too tightly and could not move with the heat. When it fails, water runs under the slates and into the timbers beneath, without necessarily showing a gap from the ground.
Inside, the clue is a brown stain on a ceiling or wall in line with the valley, often worse after long rain rather than a short shower. Debris in the valley makes it worse: leaves and moss hold water against the sides of the lead, so it spills over the edge. Railway-era houses with several roof planes may have a number of valleys, and each deserves a look.
What we fix
We clear the valley, inspect the lead from both sides and test for splits. A short run of cracked lead can sometimes be cut out and replaced with a new section, dressed into the existing lead so no gap is left. Where the whole length has aged, we strip back the slates alongside, fit new lead with the right laps and code, and relay the slates tight against it.
If the slates also need replacing, natural Welsh slate is quoted nationally at around £140 to £180 a metre squared, though the quote for your house comes after the survey. Photographs of the failed lead go into the report, so you can see the cause rather than take our word for it. For more on the lead side, see lead roofing and leadwork.