Cambridge Roofers carry out lead flashing installation and repair in Milton - here is exactly what that process involves, from the first inspection to leaving site.
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Most homeowners only see a roofer arrive and leave, with a repaired roof somewhere in between. Understanding what a proper lead work job involves helps you judge whether the work was done correctly, ask the right questions, and spot a roofer who is cutting corners. This page walks through the full process from start to finish.
Before any lead is cut or any mortar is raked out, a roofer needs to understand what has failed and why. A visual inspection from ground level using binoculars or a drone will often show the obvious - lifted flashings, open mortar joints, missing sections. But the detail inspection needs to happen from the roof surface itself, or at minimum from a ladder at the level of the flashing.
At this stage, a roofer should be checking: the Code of the existing lead (by measuring its thickness or assessing its weight and flexibility), whether the flashing has cracked or simply become unfixed, the condition of the mortar joints into which the lead is tucked, whether there is any rot in timber immediately below, and whether the problem is isolated to the flashing or whether tiles or slates nearby are contributing to the water entry.
If you are not given any explanation of what was found during inspection - just a price - that is worth questioning. The inspection findings determine what the job should involve.
Lead work on chimneys or dormers typically requires scaffolding. A chimney stack that is more than a metre above the ridge, or one that needs work on all four sides, almost always requires a full scaffold platform rather than a ladder or tower. This is not optional - it affects both the quality of the work and the safety of the person doing it.
For lower-level work - a bay window flat roof abutment, for example, or a dormer on a single-storey rear extension - a hop-up or tower scaffold may be sufficient. A roofer should be able to explain what access method they are using and why.
On a first visit, if the job requires scaffolding, a scaffold should be ordered before work starts. Attempting chimney lead work from a ladder is neither safe nor good practice, and the result reflects it.
On most repair jobs, the existing lead is removed entirely before new lead is installed. This allows the roofer to inspect what is underneath - the timber fascia, the tile or slate surface, the brick or stonework of the chimney - and deal with any secondary damage before sealing it back in.
Removal involves taking out the mortar or lead wedges from the chase, lifting the old flashing sections, and clearing the chase of any old sealant, tape or filler. If previous repairs have been made with self-adhesive tape or mastic, these need to be removed thoroughly - adhesive residue left in the chase will prevent the new lead from seating correctly.
The old lead itself can be recycled. Lead has scrap value, which is worth noting if you are being charged separately for disposal - in most cases, the scrap offsets the disposal cost.
The mortar joint or chase into which the lead will be tucked needs to be cleaned out to a consistent depth - typically around 25 mm. On brickwork this means raking out the horizontal joint between courses. On rendered or stonework surfaces, a chase is cut with a disc cutter.
At this point, any damaged brickwork or mortar at the base of the chimney stack should be attended to. Loose bricks, spalled mortar or cracked render will allow water in even if the lead is perfect, so the two jobs need to happen together.
The roof surface beneath the flashing line is also checked. If slates or tiles are broken or slipped directly below where the flashing will sit, these should be replaced now, before the new lead is dressed over them.
Lead sheet is measured, marked and cut to the correct profile for each section. A chimney back gutter, step soakers, side flashings and a cover flashing are all different shapes and require different cutting patterns. The roofer should be working from the correct Code of lead for each element - Code 4 or Code 5 for chimney flashings and back gutters, Code 3 for soakers under slates.
Dressing the lead - forming the bends, corners and drips - is done with a bossing mallet and dresser tools. The goal is a tight, clean fold without thinning the lead at the bend. A fold that has been beaten too hard will be thin at the crease and will crack with thermal movement. You can see the difference: a well-dressed fold has an even surface; an over-worked one has a slightly rippled or wavy appearance at the bend.
Each section should be cut to no more than 1.5 metres in length to allow for thermal expansion. Where a run is longer than this, a proper expansion joint - an overlap of at least 75 mm dressed to allow movement - is built in.
The dressed lead is tucked into the prepared chase and fixed with lead wedges at regular intervals - typically every 450 mm. The wedges grip the lead against the back of the chase and prevent it from dropping. Relying on mortar alone to hold the lead in place without wedges is a false economy; the mortar will crack and the lead will drop.
Once wedged, the chase is pointed with an appropriate mortar mix - typically a slightly weaker mix than the surrounding masonry to allow some movement and prevent the pointing from cracking the brickwork. The mortar is tooled to a slight weathering angle so it sheds water away from the joint.
The free lower edge of the flashing should be dressed down over the tiles or slates below with a consistent and neat drip edge, and where required, a lead tingle or clip is fixed to support longer hanging sections.
Once all sections are fixed and pointed, the roofer should check that every lap and joint sheds water in the right direction, that no section has been fixed so rigidly that it cannot expand, and that the overall arrangement is watertight. Water should be directed outward and away from every joint, never toward the roof surface or into a corner where it can pond.
If the job included removal of tiles or slates for access, these are relaid and any broken ones replaced. All cut-off lead, old mortar and debris should be cleared from gutters and the roof surface before leaving site.
A tidy site at the end of the job matters. Lead offcuts, old mortar, tile fragments and packaging should all be removed. The scaffold should be inspected to confirm nothing has been left on the platform. Gutters directly below the work area should be cleared of debris.
At handover, you should be able to see the new lead clearly from a ladder or an upstairs window - neat folds, consistent mortar pointing, and no visible gaps or lifted edges. Ask the roofer to walk you through what was done and why. If they can not explain it plainly, that is useful information.
We carry out lead work in Milton and across the surrounding area including Cambridge, Chesterton, Histon, Waterbeach, Girton, Trumpington, Sawston, Stow cum Quy and Ely. If you need a proper assessment of your lead flashings, call us and we will tell you clearly what the job involves before any work starts.
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