If you are weighing up whether to remove a redundant chimney stack on your Costessey home, understanding the materials involved and the honest pros and cons of each approach will help you make the right call.
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Before thinking about materials, you need to settle on the approach. For a chimney that is no longer used, you have two main paths: take the stack down completely and make good the roof, or retain the stack and seal it against water ingress. The right answer depends on the condition of the brickwork, the age of the property, and whether you want a long-term fix or a lower-cost short-term measure.
Sealing a redundant stack means capping the flue opening, pointing the brickwork and reflashing the base. This works well when the stack is structurally sound and the problem is limited to worn mortar or failed lead. It does not work when the brickwork has spalled, when there is visible lean or movement, or when the flashing has failed more than once in quick succession. In those cases, removal is the more honest answer.
Once the stack is down, the opening in the roof has to be made good. The choice of materials here is not arbitrary - it has to match what is already on the roof as closely as possible, and the underlying structure has to be sound before anything goes on top.
Roofs are commonly covered in either plain clay tiles or concrete interlocking tiles. These two types behave very differently when you are trying to match an infill after a chimney removal.
Plain clay tiles are the traditional choice for older properties. They come in various shades from buff through to dark red, and they weather over time to a colour that is hard to replicate with new tiles. For a chimney infill, sourcing reclaimed clay tiles from a salvage yard gives the best colour match. The honest downside is that reclaimed tiles vary in quality - some will be near the end of their useful life - and sourcing the right batch takes time. New clay plain tiles are a reliable alternative but will look noticeably brighter than the surrounding roof for several years until they weather in.
Concrete interlocking tiles are more forgiving in one sense: they have a defined profile that needs to match exactly. A Marley Monarch tile cannot be replaced with a Redland 49 - the spacing, overlap and locking system are different. Your roofer needs to identify the exact tile in use and source matching stock. The upside is that concrete interlocking tiles are still manufactured in most profiles, so a close or exact match is often available new.
Natural slate appears on some older or extended properties. Welsh or Westmorland slate is the quality benchmark, but reclaimed Spanish slate is widely used as a more affordable option. Thickness and texture vary considerably between sources, so inspect a sample against the existing roof before committing.
If you are retaining the stack rather than removing it, the flashing is the most important material decision. Lead flashing is graded by weight per square metre, referred to as Code 3 through to Code 8. For chimney flashings, Code 4 (1.8mm thick) is the minimum that should be used. Code 5 is the better choice for a step flashing on a pitched roof where the stack is large or on an exposed elevation. Thinner flashings corrode and crack faster, particularly where they are in contact with lime mortar.
Mortar flashing - a cement fillet run around the base of the stack instead of lead - is a budget shortcut that rarely lasts more than a few years before cracking. It is not a like-for-like replacement for lead. Any quote that offers mortar fillet as the flashing solution for a leaking chimney should be questioned.
EPDM rubber flashing strips are now available as an alternative to lead for some applications. They are quicker to fit and resistant to corrosion, but they are best suited to flat or low-pitch sections rather than complex step flashings on a steep pitch. For most traditional chimney flashings, lead remains the most durable material in use.
Whether you are retaining the stack or just capping the flue, the mortar used for repointing matters. A strong cement-rich mix is not automatically better - on older brickwork it can trap moisture behind a hard skin and accelerate the spalling of the brick face. A softer, more permeable mix allows the masonry to breathe and is less likely to crack at the joint. Your roofer should be matching the mortar specification to the age and type of brick, not using one mix for everything.
Chimney haunching - the sloped mortar bed that surrounds the base of the pots - is another detail that fails regularly. A good haunch sheds water away from the flue opening. A flat or poorly formed haunch pools water at the top of the stack, which is exactly where you do not want it.
When tiles are lifted to remove a stack or to carry out a reinstatement, the condition of the felt underlay and the timber battens beneath is exposed. On older roofs, the felt may be the original bitumen-bonded type, which can be brittle and cracked at the edges after decades of movement. If a section needs to be replaced, a modern breathable membrane is the right replacement material - it allows water vapour to escape from the roof space rather than trapping it against the timber.
Battens should be checked for rot, particularly at the eaves end and around any penetrations. This is the one part of the job where it pays to spend a little more now rather than re-lift tiles in five years.
A chimney capping and repoint, retaining the stack, typically costs in the region of £400-£700 for a standard single stack. A full chimney take-down and roof reinstatement on a two-storey house is more typically in the range of £800-£1,500, with larger stacks or those requiring more scaffolding sitting toward the higher end or above it. Tile matching - particularly sourcing good reclaimed clay tiles - can add cost if a salvage trip is required.
These are honest ballpark figures. An accurate price needs a look at the actual stack, the existing roof covering and the access required. Call Wymondham Roofers to arrange a survey of your Costessey property and we will go through the options with you before any work is agreed.
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