Chimney Lead Flashing Preston
What chimney flashing does
Slates and tiles can't seal against a vertical brick wall on their own. Flashing bridges the gap. On a typical chimney stack it's made up of several pieces that work together:
- Front apron: a single piece across the lower face of the stack, dressed down over the slates or tiles below it.
- Side flashings: stepped pieces running up each side of the stack, following the slope of the roof, with their top edges tucked into the mortar joints.
- Back gutter: a small lead gutter behind the stack, on the uphill side, that catches the water running down the roof and turns it round the chimney.
- Cover flashings: pieces tucked into the brickwork and dressed down over the lead below, so water can't get behind it.
Each piece overlaps the next, so water is always shed downhill and away from the stack. If one piece fails, or the overlaps aren't right, the whole detail can leak.
Signs your chimney flashing has failed
- Lead lifted or flapping, often after high winds.
- Splits or cracks in the lead, especially on long pieces.
- Gaps where the lead meets the brickwork, or mortar missing from the joint it's tucked into.
- Sealant smeared along the joint, a sign of a past quick fix that may not have held.
- A mortar fillet instead of lead, common on older or cheaper repairs, often cracked.
- Damp on the chimney breast, or on the ceiling or wall next to the stack, after rain.
- Water marks on the timbers around the chimney when you look in the loft.
Why chimney flashing fails
Movement
Lead expands and contracts as it heats up and cools down. If a piece is too long, or fixed too tightly, that movement eventually cracks it. Properly sized and fixed pieces allow for it.
The mortar it's tucked into
The top edges of the flashing are set into the mortar joints of the stack. When that pointing weathers and crumbles, the lead loses its grip and can lift. That's why flashing and repointing are often done together. See our chimney repointing page.
Quick fixes
Sealant, flashing tape and mortar fillets are often used where lead should be. They can stop a leak for a while, but they crack and come away far sooner than lead that's been fitted properly.
Code 4 and Code 5 lead
Lead sheet comes in thicknesses known as codes; the higher the code, the thicker the lead. Code 4 is widely used for flashings. Thicker Code 5 is used where the lead needs to be tougher, such as some back gutters. We use the right code for each piece. For lead elsewhere on the roof, see our leadwork roofing page.
How we renew chimney flashing
- Safe access to the stack, usually with scaffolding.
- Remove the old flashing, sealant and any mortar fillets, and check the slates or tiles around the stack.
- Rake out the joints the new lead will be tucked into.
- Cut and dress new lead for the apron, sides, back gutter and covers, each piece sized to allow for movement.
- Tuck and fix the lead into the joints, then point the joints so the lead is held securely.
- Check the rest of the stack while we're up there: the pointing, the flaunching and the pots.
If the brickwork itself is crumbling, new lead won't last on it. In that case we'll talk to you about repointing or a chimney rebuild first.
Is it the flashing, or something else?
A damp chimney breast can be caused by the flashing, but it can also come from the pointing, the flaunching on top of the stack, or rain getting in through the pots. We check the whole stack before recommending a repair, so you're not paying to fix the wrong thing. See our roof leak repairs page for how we trace leaks.
What affects the cost
Every chimney is different, so we quote after looking at it. The main things that affect the price are the size of the stack, how many pieces of flashing need renewing, the access needed to reach it safely, and whether the pointing or flaunching needs doing at the same time. Doing related work together usually saves you paying for access twice.
Older homes and conservation areas
On older homes, renewing flashing in lead, like for like, is usually the right approach. If your home is listed or in a conservation area, check with Preston City Council before making changes to the outside of a chimney.
Frequently asked questions
How do I know if my chimney flashing is leaking?
Damp on a chimney breast or ceiling next to the stack after rain, lead that has lifted or split, or water marks on the timbers around the chimney in the loft are the usual signs.
Can flashing be repaired with sealant?
Sealant is rarely a lasting fix. It cracks and comes away as the lead and brickwork move. Renewing the lead properly lasts much longer.
Do you use Code 4 or Code 5 lead?
Both. Code 4 is widely used for flashings, and thicker Code 5 where the lead needs to be tougher.
Do I need scaffolding?
Usually, yes, for safe access to the stack. We'll explain what's needed when we quote.
Should the chimney be repointed at the same time?
Often, yes. The flashing is tucked into the mortar joints, so if the pointing is failing, it makes sense to do both while access is in place.
Are your quotes free?
Yes. Call 07742 720 236 for a free quote.
Leak around your chimney?
Call Danny on 07742 720 236 or request a free quote. For all our chimney work, see our chimney services in Preston page.