Does a Chimney Need Lining?

What a chimney liner is for

A liner is a tube set inside the brickwork of the stack. It does three jobs. It contains the smoke and gases from the fire so they travel up the flue and out at the pot, and do not seep through cracks in the masonry into other rooms or the roof space. It resists the heat and the acidic condensation that burning fuel produces, which attack old mortar and brick over time. And it gives the flue a smooth, correctly sized bore, so the draught works as the appliance expects.

Most Victorian and Edwardian houses were built with brick flues parged inside with a lime-based render, and some later houses have clay liners in sections. Over the decades, parging falls away, joints between clay liners open, and the flue becomes leaky. That does not matter much if the fireplace has been shut off for years. It matters a great deal if you want to light it again.

When a liner is normally needed

These are the common situations in which lining is considered, or required.

• Fitting a wood-burning or multi-fuel stove into an existing chimney, because a stove runs hotter and its flue gases are narrower and more corrosive than those of an open fire.
• Using an old flue that is cracked, partly collapsed or known to leak smoke.
• Installing a gas appliance that discharges into a chimney, where the flue must suit the appliance.
• Repairing or rebuilding a stack, where the flue is exposed and its condition can be checked.
• A failed smoke test or camera survey, where the sweep or installer reports gaps or damaged sections.

The correct liner depends on the fuel. Flexible stainless steel liners are widely used for stoves, rigid twin-wall systems for some appliances, and clay or concrete liners or a cast-in-place lining for others. The appliance maker's instructions say what they require, and a competent installer follows them. Which type is right for your flue is not something a roofer should guess, so ask your appliance installer.

When you do not need one

If a chimney is disused and stays that way, lining it is wasted money. The flue is not carrying smoke, so the usual concerns about leaks do not arise. What it needs instead is ventilation, so damp does not accumulate. Our page on capped chimney ventilation covers that. A chimney that is capped and abandoned also does not need a liner when a stack is repaired, though the roofer will normally check the top of the flue is sound before capping it.

An open fire in a good flue may also run without a liner, if the sweep confirms the flue is sound and the fire is used lightly. That is a matter for judgement, and a sweep with a camera is the person to ask. Many householders choose to line anyway when they have had smoke leaks or damp.

What building control and the installer decide

Fitting a solid-fuel appliance is notifiable work in most cases, and the lining forms part of the assessment. The installer should tell you what is proposed, and your building control body, either the council or a private approver, signs it off. We do not give detailed regulatory advice on flues, because the answer depends on the appliance and the property. What we can say is to ask for the lining specification in writing, and keep it with your house documents, as a buyer's solicitor may later ask for it.

Where a lining is installed, it ends at the top of the stack, and the details there are roofing details. The liner must be fixed, sealed to the pot or terminal, and the flaunching around it made watertight. That is the part of the job we deal with. Our guide to chimney pots and cowls describes the terminals, and chimney flaunching covers the weatherproofing.

How to find out the state of your flue

The simplest check is a sweep's camera survey. A small camera is pushed or lowered through the flue, and the footage shows broken joints, missing parging, blockages and any previous lining. A smoke test, where a smoke pellet is lit at the base and the stack is watched for leaks, shows whether gases escape. These cost far less than relining and will tell you whether you need it. If you are thinking about a stove, get the installer to survey the chimney before you buy.

From the roof side, we look at the outside of the stack, the pot and its bedding, and the flashings. We cannot judge the inside of the flue from there, so we tell you plainly when the next step is a sweep or an installer. If the stack needs repair as well, you receive a fixed price in writing. Published UK guides put chimney repair anywhere between £500 and £2,000, and the price for yours follows the survey. See chimney sweep or roofer to see who does what, or go back to chimney repairs in Basingstoke.