Lead Flashing Coming Away From The Wall

What's happening?

Flashing is the weatherproof joint wherever a roof slope abuts something vertical — a chimney, a parapet, a house wall above an extension roof, a dormer cheek. Lead is the traditional UK material because it can be dressed to shape and lasts decades. It works by being tucked into a raked-out mortar joint, wedged, and then pointed, so water running down the wall is thrown out over the tiles rather than behind them. Lead also moves a great deal with temperature, and that movement is what eventually splits it or works it out of the joint. When flashing fails, water enters at the top of a slope and runs a long way inside before it appears, so the damp patch is rarely below the fault.

What usually causes it?

• Lead sheet cut too long between joints, so thermal expansion has nowhere to go and the lead fatigue-cracks along a fold
• Pointing above the flashing perished, letting the upstand pull free of the raked joint
• Wedges missing or never fitted, so the lead was only held by mortar
• Lead laid over a wide span in one piece rather than in stepped sections following the brick courses
• Mastic or cement-based repairs applied over old lead, which crack away and trap water behind them
• Corrosion from contact with other metals, or from run-off carrying moss and organic acids
• Lead theft or damage from earlier work such as satellite dish or cable installation drilling through the upstand

When should you call a roofer?

Call a roofer within a couple of weeks if the flashing has lifted but nothing is wet indoors, and within days if you have damp appearing on the wall or ceiling below the abutment. Bring it forward if the flashing is on a chimney, on a parapet, or above a habitable room, because those leaks reach structural timber fastest. If a long section of lead has gone missing entirely, treat it as urgent.

What will the roofer actually do?

• Set up safe access to the abutment, which usually means a tower or scaffold rather than a ladder resting on the roof
• Strip the failed flashing and any mastic or cement bodges, and inspect the brickwork, timber and tiles behind it
• Rake out the mortar joint to the correct depth, following the brick courses in steps where the roof runs up a wall
• Dress new lead of the appropriate code to shape in lengths short enough to allow thermal movement, wedge the upstand into the raked joint, re-point in a mortar suited to the wall and dress the apron down over the tiles
• Check the soaker or step flashings under individual tiles at the same time, since these fail alongside the visible apron
• Report on timber condition behind the flashing so any rot is dealt with rather than covered up