fter falling out of fashion during the 60s and 70s, many original fireplaces were replaced with gas and electric models, their chimneys bricked or blocked up. Wood burning, however, has experienced a resurgence over the past 20 years and in properties ranging from large period homes to the thousands of Victorian terraces that line our streets, homeowners are looking restore traditional modes of heating to their former glory.
Aside from the aesthetic benefits of open fires and wood-burning stoves in period properties, modern solid fuel technology has come on leaps and bounds in recent years. If wood has been properly dried before being burnt, the latest wood-burning stoves can offer up to 90% efficiency. As long as fuel is sourced from properly managed woodland, and is only burnt when it has dried and properly seasoned, it is considered a renewable and sustainable energy source. These factors have contributed to an increasing number of chimneys being reinstated.
Yet bringing chimneys back into use after many decades of neglect and misuse presents a unique set of challenges to the architects, specifiers and contractors working on the project. Before an effective solution can be identified, a close inspection of the chimney is required, checking for signs of degradation, both inside and out.
Exposed to the elements for years on end, porous clay bricks, lime mortar and traditional terracotta chimney pots can easily fall into disrepair. Brickwork and mortar on the outside of the chimney and stack can become cracked and damaged, allowing water to penetrate and freeze leading to further erosion.
Turning to the interior, brickwork and mortar can suffer due to the combination of sulphates in the flue gases and moisture, from water penetration or condensation build-up. This chemical reaction produces a weak sulphuric acid which slowly erodes brickwork and mortar inside the chimney. Damp spots or staining on the chimney breast and the adjoining walls are usually caused by condensate or tar seeping through cracks in the flue; a sure sign that the construction of the chimney is compromised.
Houses built prior to the 1965 Building Regulations were not subject to strict safety standards as they are today and chimneys were commonly constructed without a sufficient lining. Instead, a rough coat of lime mortar would be applied to minimise leakage of flue gases; a practice known as ‘parging’ or ‘pargetting’. This soft render provides little resistance to the acids and particulate matter produced during combustion, and over time it will deteriorate. Further damage will occur when the chimney is swept, loosening the crumbling render and bringing it down the chimney.
Thatching, shingles and timber frames
Aside from structural issues, heritage renovation projects present additional challenges in terms of combustible materials. You might encounter timber beams inside the chimney breast, or roofs may be thatched or laid with timber shingles. These character features must be protected, especially if the property is listed, and renovation work must be carried out sensitively and in keeping with the building’s original structure and qualities, while ensuring that safety standards are not compromised; a tall order at times.
By far the easiest and safest option to bring properties of this type up to scratch in terms of performance and safety is to reline the chimney in its entirety with a modern fit-for-purpose liner.
On a thatched- or shingle-roofed property, using a pumice-based system, such as Schiedel’s Isokern range, provides a safe solution thanks to the naturally insulating properties of this volcanic material. An extremely effective and robust insulator, pumice effectively eliminates heat transfer into adjacent, potentially combustible materials, maximising its ability to withstand chimney fires while increasing efficiency.
Maintaining a high internal flue temperature is essential for two reasons; it ensures that flue gases remain hot, so they continue to rise, expelling the harmful products of combustion and preventing carbon monoxide from entering living spaces. Additionally, it prevents the build-up of creosote and tar in the chimney, reducing the risk of chimney fire. To withstand these temperatures, a robust and fire-resistant structure, therefore, is essential, and, in fact, many insurance companies specify that thatched homes must have an insulated flue, providing an extra level of protection in the event of a chimney fire.
Apart from traditional ceramic flue liners, flexible stainless steel liners are particularly useful for relining chimneys. It was common in old properties to have one chimney serving several fireplaces – something that is quite rightly considered as sub-standard today. Products such as our Technoflex Plus enable you to overcome this issue by plotting the flexible liner through bends in the chimney. The liner has a corrugated outer skin and engineered joints to give it strength, and the smooth inner skin allows for easy drainage down of condensates, so there is less opportunity for soot to collect in the bends.
Specialist coatings, such as Schiedel’s Isokoat, can also work well if the chimney is easily accessible, as is often the case in old inglenook fireplaces. A liquid sealant is applied to the inside of the chimney to create a physical barrier. Applied under pressure, the liquid is forced into cracks and fissures in the mortar joints, brick and stonework, strengthening the flue wall and providing a safe and effective seal.
With solutions such as these, renovations can remain sympathetic to their original features without compromising on safety – bringing modern comforts to historical homes.