Chimneys, Fireplaces and Flues in Historic Buildings: Repair, Relining and Safe Use

A conservation guide to chimneys, fireplaces and flues in historic buildings: how they work, how to read their condition, how to repair stacks and relining flues safely, fitting stoves, keeping disused chimneys dry, and the consent and regulations involved.

Building Restoration Index — Technical Library. By Paul Stenning and Mike Walters, Historic Buildings Advisors, Tuscan Foundry Products.

How a historic chimney works

A chimney is a vertical masonry structure that carries smoke and gases out of the building, and it depends on several parts working together.

• Fireplace and hearth. The opening, with its grate, cheeks, back and surround, sits on a non-combustible hearth.
• Throat and smoke shelf. The narrowing above the fire speeds up the gases and helps prevent downdraughts.
• Flue. The passage through the chimney breast and stack. In older chimneys, flues were lined with a lime render called parging, made with lime and sometimes cow dung, to seal the joints and smooth the passage.
• Withes. The thin brick or stone divisions between flues in a stack with more than one flue.
• Stack. The part above the roof, often of finer brick or stone, sometimes with decorative caps and oversailing courses.
• Pots and flaunching. Clay pots on top of the stack, bedded in a sloping mortar capping called flaunching that throws water off the top.
• Flashings. Lead flashings, soakers and back gutters where the stack meets the roof keep the junction watertight.

Chimneys are also part of how a historic building ventilates itself. An open flue draws air through the room, which helps carry moisture away.

Why historic chimneys matter

Chimneys are often a key part of a building’s character and are frequently mentioned in list descriptions. Tudor clustered and decorated stacks, Georgian stacks on party walls, Victorian pots and terracotta caps all help date a building and shape its roofline. Inside, fireplaces and surrounds are often among a room’s most significant features.

Removing or lowering stacks, changing pots, removing chimney breasts or replacing fireplaces can harm significance and may need consent. Like-for-like repair is almost always preferable.

Reading the condition of a chimney

A chimney should be inspected regularly from the ground with binoculars, from the roof space and, where safe access exists, close up. Look for:

• Leaning or bowing. A stack that leans, often away from the prevailing weather, may be suffering from sulphate attack. Sulphates from burning coal and other fuels condense in the flue, react with the mortar and make it expand, so one side of the stack grows taller than the other. A structural engineer or experienced surveyor should assess a leaning stack.
• Eroded or missing pointing, open joints and loose bricks or stones.
• Cracked or failed flaunching and cracked, loose or missing pots.
• Spalling of brick or stone faces from frost and soluble salts.
• Vegetation growing from joints or the top of the stack.
• Failed flashings, staining and damp in the roof space or on the chimney breast below.
• Tar or brown staining on the chimney breast inside, which suggests condensation in the flue or a failing flue.

What causes the damage

Most chimney problems come from exposure to weather combined with attack from inside by the products of combustion.

• Weather. Stacks stand above the roof, exposed on every side. Driving rain, frost and wind wear away mortar and masonry faster than on walls below.
• Combustion products. Sulphates, acids and tars from fuel condense in the flue, especially when the flue is cold or the fuel is wet. They break down parging and mortar and stain plaster on the chimney breast.
• Cement repairs. Cement pointing, flaunching or render traps moisture in softer brick and stone and makes spalling worse.
• Loss of ventilation. A flue sealed top and bottom collects condensation and rainwater and can cause damp patches on the breast.
• Water from roofs. Failed back gutters, flashings and adjacent gutters soak the base of stacks.

Repairing a chimney stack

Repair should keep as much of the original stack as possible, using matching materials and lime mortars.

• Repointing. Rake out failed mortar by hand and repoint in a lime mortar to match the original. See our guide to historic brickwork.
• Replacing units. Cut out and replace spalled bricks or stones with matching reclaimed or new units, rather than rendering over damage.
• Flaunching. Renew failed flaunching in lime, shaped to shed water, and rebed loose pots.
• Pots. Repair or replace cracked pots to match the originals in shape, height and colour. Reclaimed pots are often available.
• Flashings. Renew lead flashings, soakers and back gutters as needed. See our guide to historic roofs, coverings and leadwork.
• Rebuilding. Where a stack is unstable and has to be taken down, record it first with photographs and measured drawings, number and set aside sound bricks or stones, and rebuild to the same design and height, reusing as much as possible.

Chimney work is high up and exposed. It needs safe access by scaffold or, for tall stacks on churches and large buildings, steeplejacks. Never work from ladders on the roof.

Inspecting a flue

Before any flue is brought back into use, it should be swept, inspected and tested.

• Sweeping removes soot, debris and birds’ nests, and is the first step to seeing the flue’s condition.
• Smoke test. A smoke pellet lit in the fireplace with the top of the flue sealed shows whether smoke leaks into other rooms, the roof space or neighbouring properties.
• CCTV survey. A camera lowered through the flue shows the condition of the parging, withes and joints and any blockages.
• Draw test. Checks the flue is pulling properly.

Shared flues and party-wall chimneys need particular care, as leaks may affect neighbours. A failed smoke test means the flue must be repaired or lined before use.

Lining a flue

Lining is often needed to make an old flue safe and efficient for a modern appliance, but each type of liner has consequences for the historic fabric.

• Flexible stainless steel liners are dropped down the flue from the top. They are relatively quick to install and need little disturbance, but they must be the right grade for the fuel and appliance, have a limited life and need the flue to be large enough.
• Rigid sectional liners of pumice, clay or ceramic are built into the flue in sections. They are durable but usually need openings cut into the chimney breast at bends, which can damage plaster, panelling or decoration.
• Cast-in-situ liners are formed by pumping an insulating mix around an inflatable former in the flue. They can follow bends and stiffen a weak chimney but add weight and are effectively irreversible.
• Coating systems apply a ceramic or similar lining to the inside of the existing flue. Their suitability depends on the flue’s condition and the appliance.

The choice should take account of the appliance and fuel, the shape and condition of the flue, the structural capacity of the stack, how much historic fabric would be disturbed and whether the work can be reversed. On a listed building, lining a flue may need consent. Restoring the parging with lime is sometimes possible for open fires in good flues.

Stoves in historic fireplaces

A wood-burning or multi-fuel stove can be fitted into a historic fireplace, but the installation must meet building regulations and should not harm the fireplace or surround.

• Building regulations. In England and Wales, installation of solid fuel appliances is covered by Part J. Use a HETAS-registered installer, who can self-certify the work, or notify building control.
• Hearth and clearances. The stove needs a hearth of the right size and construction, and clearances to combustible materials such as timber lintels, beams and panelling.
• Carbon monoxide alarm. A carbon monoxide alarm is required when a new solid fuel appliance is installed in England, and fitting one with any fuel-burning appliance is strongly recommended.
• Register plate and liner. Most stoves need a register plate closing the base of the flue and usually a liner connected to the flue outlet.
• Clean air rules. In smoke control areas, only exempt appliances or authorised fuels may be used, and in England there are restrictions on the sale of wet wood and traditional house coal.

Choose a stove that fits within the fireplace opening without removing historic grates, tiles or brickwork. Keep any removed grate or insert, labelled, so the fireplace can be returned to its original form.

Open fires and smoking chimneys

Many historic fireplaces can still be used as open fires, but smoking is a common problem with a number of causes.

• Not enough air. Draughtproofing and new windows can starve a fire of air. An air vent near the fireplace may solve it.
• Opening too large for the flue. A canopy, raised hearth or reduced opening can help.
• Cold or damp flue. A flue that hasn’t been used for a long time may need warming up with a small fire before it draws.
• Downdraught. Nearby trees, taller buildings or the roof shape can push air down the flue. Raising the pot or fitting a cowl may cure it, but cowls change the appearance of the stack.
• Blockages. Birds’ nests, debris and soot.

Solve the cause rather than adding visible fittings where possible.

Disused chimneys and chimney breasts

A chimney no longer in use still needs care: it should be ventilated, kept watertight and left structurally intact.

• Capping. Fit a ventilated cap or a cowl with rain protection to stop rain entering while allowing air to move.
• Ventilation. Leave a vent or grille at the fireplace so air can flow up the flue. A sealed flue collects condensation and causes damp patches and staining on the breast.
• Removing breasts. Removing a chimney breast can undermine the stack above, which may be left hanging on the structure. It needs structural support designed by an engineer, building regulations approval and, on a listed building, consent. It may also affect a party wall and need notice to a neighbour.
• Removing stacks. Taking down or lowering a stack can harm the building’s character, and it is unlikely to be acceptable on a listed building or in a conservation area.

Fireplaces, grates and surrounds

Historic fireplaces, from stone inglenooks to Georgian hob grates and Victorian tiled inserts, are often highly significant and should be repaired in place.

• Surrounds. Stone and marble surrounds can be cleaned, repaired and refixed by conservators or masons. Avoid harsh cleaning and acid-based products.
• Cast iron grates and inserts. Cracks and broken parts can often be repaired, and missing parts copied. Cast iron is traditionally finished with blacklead or a stove polish.
• Tiles. Decorative tiled cheeks can be refixed, and missing tiles replaced with reclaimed or matching tiles.
• Theft and salvage. Historic fireplaces are frequently stolen or removed. If you buy a reclaimed fireplace, ask about its provenance. Removing a fireplace from a listed building without consent is an offence.

Fire safety in historic chimneys

Chimney fires and fires spreading from flues are a serious risk in historic buildings, particularly those with timber built close to or into the chimney.

• In many old buildings, beams, joists and lintels were built into or close to flues. Over time, heat and failed parging can let fire reach them.
• Thatched buildings are at particular risk from sparks and from fire travelling through the stack.
• Tar and soot build-up from burning wet wood or slumbering a stove overnight increases the risk of chimney fire.
• A smoke test, CCTV survey and lining where necessary reduce the risk before a flue is used.
• Fit smoke and carbon monoxide alarms, and have a fire extinguisher or blanket within reach.

Sweeping and maintenance

Regular sweeping is the simplest way to keep a flue safe. HETAS recommends sweeping at least twice a year when burning wood and at least once a year for smokeless fuels, ideally before the heating season.

• Use a registered sweep, for example one approved by HETAS or a member of a recognised sweeping association, and ask for a certificate.
• Burn dry, seasoned wood and avoid slumbering stoves overnight.
• Check stacks, pots and flashings after storms and in the annual building inspection.
• Birds, especially jackdaws, nest in chimneys. Fit bird guards outside the nesting season, as nesting birds are protected by law.
• Keep gutters, hoppers and valleys around the stack clear, so water doesn’t soak the base of the chimney.

Consent and regulations

Several sets of rules can apply to work on historic chimneys.

• Listed Building Consent is likely to be needed for rebuilding or altering stacks, changing pots, removing chimney breasts or fireplaces, lining flues and installing stoves. Like-for-like repairs may not need it, but check with the conservation officer. See our guide to Listed Building Consent.
• Building regulations apply to new appliances, flue liners and chimney breast removal.
• Planning permission may be needed in conservation areas for changes to stacks or new flues.
• Party Wall Act notices may be needed in England and Wales for work to shared chimneys.
• Clean air and smoke control rules control appliances and fuels.

Choosing contractors

Chimney work often needs several specialists.

• A registered chimney sweep for sweeping, smoke tests and CCTV surveys.
• A HETAS-registered installer for stoves and liners.
• A bricklayer or mason experienced in lime for stack repairs.
• A leadworker or roofer for flashings.
• A structural engineer for leaning stacks, chimney breast removal or heavy liners.
• A conservation architect or surveyor to coordinate work on listed buildings.

Ask for experience of historic chimneys and references.

Common mistakes

Mistake	Consequence
Repointing or flaunching a stack in cement	Moisture trapped in the masonry, faster frost damage and spalling
Sealing a disused flue top and bottom	Condensation, damp and staining on the chimney breast
Using a flue without sweeping, inspection and a smoke test	Smoke and gases leaking into rooms or neighbouring property, and risk of chimney fire
Fitting the wrong liner for the appliance or flue	Early failure, poor draw and possible fire risk
Removing a chimney breast without structural support	Collapse risk to the stack above
Removing historic grates or tiles to fit a stove	Irreversible loss of significant fabric
Rebuilding a leaning stack without investigating the cause	The problem recurring, or unnecessary loss of a historic stack
Burning wet wood or slumbering stoves overnight	Tar build-up, flue damage and chimney fires
Fitting bird guards during the nesting season	Breaking wildlife law
Changing stacks or pots on a listed building without consent	Enforcement action and loss of character

Find a specialist

Specialists in the Building Restoration Index who work on historic chimneys, fireplaces and flues, grouped by the part they play in a project:

Contractors and craftspeople

• Chimney & Flue Systems — chimney sweeps, flue lining and chimney specialists
• Brickwork — repointing and rebuilding brick stacks in lime
• Stone and Stonework — repair of stone stacks, caps and surrounds
• Leadwork — flashings, soakers and back gutters around stacks
• Steeplejacks & Lightning Protection — access to tall stacks and chimneys on large buildings
• Heating and Plumbing — stoves, boilers and heating connected to flues

Architects, surveyors and engineers

• Structural Engineers — leaning stacks, chimney breast removal and heavy liners
• Architects — coordinating work and consent on listed buildings
• Surveyors — condition surveys of chimneys and roofs

Consultants and designers

• Heritage Consultants — significance of chimneys and fireplaces for consent
• Interior Consultants & Conservators — historic interiors and fireplaces

Investigation and recording

• Non-Destructive Investigations — surveys of flues and concealed structure
• Aerial Drone Surveys — inspecting stacks without scaffolding

Material suppliers

• Fireplaces — historic and reproduction fireplaces, grates and surrounds
• Architectural Salvage — reclaimed pots, fireplaces and matching bricks
• Lime Mortars & Plasters — lime mortars for pointing and flaunching
• Brick Suppliers — matching bricks for stack repairs

Advice and training

• Organisations — national amenity societies and trade bodies, including those that publish technical advice
• Courses, Training & Events — courses and events for owners, contractors and professionals

Further reading from Tuscan Foundry

• Breathing walls: cast iron airbricks and free airflow
• Cast iron airbricks and vents from Tuscan Foundry
• Gutter and roof maintenance for heritage buildings

Related guides

• Historic roofs, coverings and leadwork
• Historic brickwork: repointing, repair and cleaning
• Energy efficiency and heating in historic buildings
• All guides in the Technical Library

The Index lists specialists without endorsement; check experience, references and insurance before appointing anyone. Specialists can add a free listing.

Frequently asked questions

Why is my chimney stack leaning?

Often because of sulphate attack: sulphates from burnt fuel condense in the flue and make the mortar expand on one side, usually the side exposed to the weather. Structural problems and failed foundations can also cause it. Have it assessed by a structural engineer or experienced surveyor.

Should a chimney stack be repointed in lime or cement?

In lime, to match the original mortar. Cement traps moisture in softer brick and stone and makes frost damage worse. The flaunching at the top should also be lime-based.

Can I use an old fireplace again?

Often yes, once the flue has been swept, inspected with a smoke test and repaired or lined if needed. A fireplace that has been disused for a long time may need work before it is safe.

Do I need to line my chimney for a wood burner?

Usually, yes. Most stove manufacturers and installers recommend a liner, and the flue must be suitable for the appliance. A HETAS-registered installer can advise and certify the work.

Which flue liner is best for a historic chimney?

It depends on the appliance, the flue and the building. Flexible steel liners cause least disturbance; sectional liners are durable but often need openings cut in the breast; cast-in-situ liners follow bends but add weight and are hard to reverse.

Do I need Listed Building Consent to fit a stove?

Often yes, especially if a liner, register plate or changes to the fireplace or stack are involved. Check with the conservation officer before work starts.

Is a carbon monoxide alarm required?

In England, a carbon monoxide alarm is required when a new solid fuel appliance is installed, and fitting one with any fuel-burning appliance is strongly recommended.

How often should a chimney be swept?

HETAS recommends at least twice a year when burning wood and at least once a year for smokeless fuels, ideally before the heating season.

Should I block up a chimney I no longer use?

Cap it with a ventilated cap to keep rain out and leave a vent at the fireplace. A flue sealed at both ends traps moisture and causes damp on the chimney breast.

Can I remove a chimney breast?

Only with structural support for the stack above, designed by an engineer, and with building regulations approval. On a listed building it needs consent, and in shared walls a party wall notice may be needed.

Why does my open fire smoke?

Common causes are not enough air in the room, an opening too large for the flue, a cold flue, downdraught from nearby trees or buildings, or a blockage. A sweep or chimney specialist can diagnose it.

What is chimney parging?

A lime render traditionally applied inside flues to seal the joints and smooth the passage. When it breaks down, smoke can leak and tar can stain plaster on the chimney breast.

Why are there brown stains on my chimney breast?

Usually from tar and condensation in the flue soaking through the masonry, especially where the parging has failed or wet fuel has been burnt. The flue needs investigation and may need lining.

Can I stop birds nesting in my chimney?

Yes, with a bird guard or cowl, but fit it outside the nesting season as nesting birds are protected by law. Have any existing nests removed by a sweep.

How do rainwater goods affect chimneys?

Blocked valleys, back gutters and nearby gutters overflow onto the base of stacks and saturate the masonry, which speeds up frost damage and causes damp below. Keeping gutters and flashings around stacks clear protects the chimney.