Ely Roofers carries out full chimney rebuilds in Haddenham, and this page explains the materials involved so you can make an informed choice before any work begins.
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A chimney rebuild is not a single product. It is an assembly of several different materials, each doing a specific job. Brick, mortar, DPC, lead flashing, flaunching and pot - all of these need to be chosen and fitted correctly. Getting one of them wrong can undermine everything else. This page goes through each element honestly, including where there are genuine options and where there really is only one right answer.
The most visible decision in a chimney rebuild is what bricks to use. You have three broad options: new bricks from a builders' merchant, reclaimed bricks salvaged from demolition, or purpose-made reproduction bricks.
New bricks are widely available and generally the most straightforward to source. The drawback is that modern facing bricks are often pressed or wirecut in a way that looks obviously different from hand-made or stock bricks used on older properties. If your property is pre-1940, a new brick is likely to look out of place unless a very close match is found. On a modern property with machine-made brickwork, a new brick match is usually achievable.
Reclaimed bricks are often the best match for older properties, particularly those built with handmade or multi-coloured stock bricks. A good builder's yard in Cambridgeshire will hold a range of reclaimed bricks and can often find a reasonable match with a sample. Reclaimed bricks have already weathered, so they blend in quickly. The drawback is that they may carry old mortar residue, they vary in quality, and sourcing enough of one type can take time. They are also sometimes more expensive per brick than new equivalents.
Reproduction or purpose-made bricks are manufactured to replicate specific historical sizes and textures. They can be an excellent match but cost more, and lead times from some suppliers can be several weeks. For a listed property or a building in a conservation area, a reproduction brick may be the only option that will satisfy a planning condition.
Our practical advice: bring a sample brick from the existing stack to any roofer you ask to quote. It gives them something to match against and makes the sourcing conversation specific rather than vague.
Mortar is the element most often mishandled in chimney work, and the consequences take a few years to show, by which time the original roofer is long gone.
The correct mortar mix depends on the age of the building and the strength of the bricks. Older properties built before the mid-twentieth century were generally built with lime-based mortars. These are softer and more flexible than cement mortars. They allow the stack to move slightly in wind (all chimneys flex to a degree) without cracking. When a hard cement mortar is used to repoint or rebuild a stack originally built in lime, the mortar becomes stronger than the bricks. Frost movement then cracks the bricks rather than the joints, which is the opposite of what the system is designed to do.
For most pre-1960 domestic chimneys, a mortar with a significant lime content is the right choice. For newer properties with engineering or machine-made bricks, a stronger mortar is appropriate. A roofer who uses the same bagged mix on every job regardless of the building type is not doing the job properly.
A damp proof course (DPC) at the point where the chimney stack meets the roof is not optional in a rebuild done to current building standards. It is a physical barrier, usually a specialist roofing DPC membrane, that prevents moisture from wicking upward from the roof junction into the brickwork above.
Some older chimneys were built without one. When the original fails or was never installed, moisture rises into the lower courses of the stack and starts breaking down the mortar from below. A rebuild that does not include a new DPC at this junction is not a complete job, regardless of how neat the brickwork looks.
There is no meaningful choice to make here between options. The DPC should be installed as a matter of course. If a roofer's quote does not mention it, ask specifically whether it is included.
Lead is the standard material for chimney flashings and has been for centuries. It is malleable, long-lasting and seals well against both the brickwork and the roof covering. Properly installed lead flashings on a chimney rebuild should last several decades before they need attention.
The alternatives you may come across are aluminium flashing tape, flexible rubberised membranes and various proprietary sealants. These are sometimes used as patch repairs on existing flashings rather than as full replacements. As a permanent flashing material on a rebuilt chimney, none of them perform as reliably as lead over the long term. They are cheaper to supply and quicker to fit, which is why they appear, but a chimney rebuild is the right moment to fit lead properly rather than cut costs on the element most exposed to the weather.
Lead flashings on a chimney have two main components: the apron flashing at the front (where the roof slope meets the chimney face) and the step flashings up the sides, interwoven with soakers between each course. The back gutter flashing at the upper side of the chimney is the most critical piece, because it is where the most water collects. All of these need to be cut, dressed and fixed correctly into the mortar joints, not simply pushed against the surface and sealed.
Code 4 lead (1.8mm thick) is the minimum for flashings. Code 5 is used on wider flashings or back gutters where a heavier gauge is appropriate. A roofer should be able to tell you which code they are using and why.
The chimney pot sits on a bed of mortar called flaunching, which is shaped to slope away from the pot and shed water. Flaunching hardens with age and eventually cracks, allowing water to get beneath the pot and into the top of the stack.
In a rebuild, the pot should be re-set on fresh flaunching as a minimum. If the pot itself is cracked or badly weathered, replacing it makes sense at the same time. Clay pots are the traditional and most widely available option. They come in a range of heights and profiles. Matching the style to the other pots on the property is worth doing, since mismatched pots are visible from the street. Reclaimed pots are available for older properties where a particular style is needed.
If the chimney is no longer in use, capping or cowling the pot prevents rain and birds entering the flue. A simple clay half-round cap or a ventilated cap (which allows the flue to breathe without letting rain in) are both practical choices.
A chimney rebuild on a standard domestic property typically costs between £1,500 and £3,500. Where reclaimed or reproduction bricks are required, where the stack is tall or difficult to access, or where the flue liner also needs replacing, costs can exceed that range. Scaffold costs (where required) are usually additional to the rebuild price itself, and a chimney of any height will need some form of safe access.
Any quote given without a physical inspection from scaffold or a roof ladder is not reliable. The number of courses to rebuild, the condition of the remaining brickwork, the brick sourcing and the flashing arrangement all affect the final figure, and none of those can be assessed accurately from the ground.
If you have a chimney that needs assessment, call us to arrange a roof survey and we will give you an honest view of what is needed before any work is agreed.
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Call any time. Calls are answered day and night and passed straight to our roofers.
