Lead Work And Flashings
Across North Wales
Dressed, Not Stuck On

A chimney needs a complete set of details working together: an apron to the front, stepped flashings and soakers up each side, and a back gutter behind. Any one of them missing or wrong and the stack leaks. On slate roofs, individual soakers are essential: cover flashing alone cannot keep water out of the slate courses.

Where an extension roof abuts an existing wall, a stepped cover flashing cut into the bed joints is the correct answer. Cement fillets, still common on older repairs, crack as the two structures move relative to each other and are one of the most frequent causes of persistent leaks we are called to.

Lead-lined valleys carry the water off two pitches into one channel and take more flow than anything else on the roof. They need adequate width, correct lead code, proper drips or laps to allow expansion, and clean cut slate or tile edges either side that will not obstruct flow.

Parapet and box gutters behind a wall are the highest-risk detail on any building, because if they overflow the water goes inside rather than outside. They need generous lead, correctly formed drips, and outlets sized and kept clear. On heritage buildings we renew them in traditional form.

Velux and other rooflights come with proprietary flashing kits, and on most modern roofs they are the correct solution. Where a kit does not suit, a non-standard kerb, an unusual covering, or a heritage roof where a proprietary kit would look wrong, the surround is formed in lead instead.

Dormer cheeks, soil vent pipes, flue penetrations and mechanical fixings through a roof all need a lead detail that allows the roof to shed water past them without relying on sealant. Sealant has a place as a secondary measure; it is never the waterproofing.

Lead is specified by code, which corresponds to thickness. Soakers and small details use lighter codes; flashings, valleys and gutters use heavier ones. Under-specifying is the most common way a lead detail fails early: the thin lead work-hardens at the fold and splits.

Every piece has a maximum recommended length because lead moves considerably with temperature. Exceed it and the lead ripples, then splits at the fixings. That is why properly formed lead work is made up of overlapping pieces with drips and laps rather than one long run.