Chapter 1: Why does water overflow at the valley on our Grayshott villa after heavy rain?
What we find
A valley is the internal angle where two roof slopes meet, and on a house with several gables there may be five or six of them. Each one collects the run-off from two slopes and funnels it down to the gutter, so it takes more water than any other part of the roof. In the older houses the valley is often lined with lead, or formed from tiles cut to curve into the angle.
Leaf litter and pine needles settle in the channel and dam it. Water backs up, spills over the lead edge and soaks the underlay beneath the tiles. Sometimes the lead itself has cracked after generations of expansion in summer and contraction in winter. Inside, the stain usually appears on the ceiling of a bedroom or landing under the angle, and it gets worse each time it rains hard.
What we fix
We clear the valley by hand and look at what is underneath. If the lead is intact and was only choked with debris, cleaning may be all that is needed, and we say so. Where the lead has split or the laps are too short, we strip the adjacent tiles, lay new lead to the correct code with proper laps and a clip-fixed edge, and relay the tiles so the roof looks as it did.
On a roof with many valleys, we check every one on the same visit, because the fault often repeats. A chimney-side valley may share a flashing with the stack, and we deal with the two together. Our lead roofing and leadwork service explains how lead is specified, and you see photographs of each repair before we leave.