Chimneys and their flashings cause more leaks than any other part of a roof. Here is what each job costs and what separates a twenty year repair from a two year one.
Why the chimney leaks before the roof does
A chimney is a masonry box pushed through a waterproof surface, exposed on all four sides, and heated and cooled differently from everything around it. Every junction it creates has to be sealed with a material that can move, which is why lead is used and why cement fails.
The most common fault we attend is a cement fillet where a lead flashing should be. Cement is rigid, the stack moves, the fillet cracks, and water runs straight down inside the stack into the ceiling below. It is cheap to install and expensive to live with.
Repointing a stack runs 280 to 650 pounds depending on height and access. Re bedding the pot and renewing the flaunching is 350 to 750. Full lead flashing renewal, meaning new step flashings, soakers, front apron and back gutter, is 450 to 950 on a standard stack.
A partial rebuild from roof level up, with new brick, flaunching, pot and flashings, sits at 1,400 to 3,500 pounds and needs scaffolding. Removing a redundant stack down to below roof level and making good the covering typically runs 900 to 2,000.
Lead code, and why it appears on a good quote
Lead is specified by code, which is its thickness. Code 4 is the normal minimum for soakers and step flashings on a domestic chimney. Code 5 is used for aprons, back gutters and anywhere water concentrates or the piece is large.
Sheet size matters as much as thickness. Lead expands and contracts a long way with temperature, and an over long piece will split at the fixings within a few years. Any quote that names the code and mentions individual pieces rather than one continuous run is written by someone who knows this.
How to spot poor chimney work from the ground
Look for grey mortar wedges where a shiny grey metal step pattern should be. Look for lead that has been fixed with a bead of silicone along its top edge rather than dressed into a raked out mortar joint and wedged. Look for a single long strip of lead running up a slope instead of stepped pieces.
Inside the loft, staining down one side of the stack after driving rain is the tell. If it appears only when rain comes from one direction, the flashing on that side has failed.
How much does it cost to replace chimney flashing?
Typically 450 to 950 pounds for full lead renewal on a standard domestic stack, including access. Simple re dressing and repointing of sound existing lead is less.
Can chimney flashing be repaired rather than replaced?
If the lead is sound and has simply pulled out of the joint, it can be re dressed, wedged and repointed. Lead that is split, thinned or has been repeatedly patched with mastic should be renewed.
Do I need scaffolding for chimney work?
Almost always for anything above eaves level. A tower may be enough on a bungalow or a low stack. Scaffolding usually adds 500 to 1,500 pounds depending on height and duration.
Should I remove a chimney I no longer use?
Only if it is in poor condition or you have no plan to use the fireplace. A capped and ventilated stack costs far less to maintain than a removal, and removals can affect the look of a terrace or a period property.
The sloped mortar bed on top of the stack that holds the pot and sheds water. It cracks with age and lets water into the brickwork, and it is one of the cheapest things to put right.
Evans Roofing & Maintenance Ltd, Witney, Oxfordshire. Call 07960 482233 for a free written quote.