If your new build home includes a fireplace, chimney or flue system, it’s essential to understand the standards that govern their installation. Whether you have a traditional open fire, a contemporary gas fireplace, or an oil-fired heating system, these installations must meet strict safety and performance requirements set out in NHBC Standards Chapter 6.8.
Many homeowners are surprised to discover just how complex these installations are from a technical perspective. A fireplace isn’t simply an aesthetic feature, it’s a sophisticated system that must safely remove combustion gases from your home whilst preventing fire risks, protecting the building structure, and resisting weather and damp penetration. When installations don’t meet the required standards, the consequences can range from poor performance and damp problems to serious safety hazards.
Fireplaces, chimneys and flues operate at extremely high temperatures and carry potentially dangerous combustion gases. Materials used in chimney construction for solid fuel installations must be capable of withstanding fluctuating temperatures up to 1,100°C. At these temperatures, adequate separation from combustible materials is absolutely critical, as is the correct installation of flue liners, proper ventilation for combustion air, and appropriate weatherproofing where chimneys penetrate the roof.
The NHBC Standards address all of these concerns in detail, providing specific requirements for different fuel types. Solid fuel installations (for wood burners or coal fires) have the most stringent requirements due to the higher temperatures involved. Gas installations must comply with Gas Safety Regulations and can only be installed by Gas Safe Registered professionals. Liquid fuel systems, typically oil-fired boilers, have their own specific requirements that vary depending on the operating temperatures of the appliance.
What the Standards Cover
The standards provide comprehensive guidance across every aspect of fireplace and chimney installation. This begins with ensuring that proper design information is provided to site supervisors and contractors, specifying exactly what can be installed and which fuels can be used. Many homeowners don’t realise that fireplaces in new builds are often designed with limitations on the type of appliance that can be fitted, and installing the wrong type could potentially void warranties or create safety issues.
For hearth construction, the requirements specify minimum thicknesses, appropriate materials, and correct separation from combustible elements. Constructional hearths for solid fuel appliances typically require at least 125mm of non-combustible material, with specific rules about what can and cannot be placed underneath. Gas appliances may have less stringent requirements if their surface temperatures remain below certain thresholds, but hearths must still be clearly marked to prevent homeowners from inadvertently placing combustible materials too close to the appliance.
Combustion air supply is another critical area that’s often misunderstood. Every type of fuel-burning appliance requires an adequate supply of fresh air for combustion. Without this, appliances cannot burn fuel efficiently and may produce dangerous levels of carbon monoxide. The standards specify that this air supply must come from outside, either directly or indirectly, and must comply with Building Regulations. Unfortunately, some homeowners unknowingly block these ventilation openings when decorating or making alterations, potentially creating hazardous conditions.
The chimney structure itself must provide adequate support for the flue liner whilst protecting adjacent building elements from heat and combustion gases. For masonry chimneys, this involves careful attention to foundation design, appropriate mortar selection (including sulfate-resistant cement in exposed locations), proper bonding to adjacent walls, and adequate wall thickness. Factory-made insulated chimneys offer an alternative and must be installed strictly according to manufacturer’s instructions with a design life of at least 30 years.
Flue Liners and Terminals
Flue liners are essential components that protect the chimney structure and ensure efficient removal of combustion gases. They must be installed with sockets or rebates facing upwards, properly sealed at joints, and supported by weak insulating concrete (never ordinary concrete) in the space between the liner and surrounding masonry. The standards are very specific about which materials are acceptable, with flexible flue liners explicitly not permitted in new build properties.
At the top of the chimney, terminals must be correctly designed to assist flue function and prevent weather penetration. They should be positioned in low-pressure zones where possible, taking account of prevailing winds and nearby obstructions. Chimney cappings must project sufficiently to shed water clear of the masonry and, in exposed locations, specific detailing with damp-proof courses and flashings is required to prevent moisture ingress.
Fireplace Surrounds and Safety
An often overlooked aspect is the proper fixing of fireplace surrounds. These can be substantial in weight, and the standards make clear that fixings relying solely on adhesive are not acceptable. Mechanical fixings of appropriate strength and durability must be used, with full consideration given to the potential for overturning. This is particularly important in homes with young children who might be tempted to climb on fireplace features.
Weatherproofing and Damp Prevention
Where chimneys penetrate the roof, careful detailing is required to prevent water ingress. This involves a combination of DPCs, flashings and cavity trays, with specific requirements depending on the exposure of the location and the pitch of the roof. Lead remains the most common material for flashings due to its durability and workability, though it must be protected with bitumen coating where it contacts cement mortar.
Chimneys that exit close to the ridge of a pitched roof may experience occasional damp penetration, which is considered acceptable provided the roof space is well ventilated and moisture doesn’t reach living areas. However, chimneys exiting near eaves or through flat roofs must be detailed to prevent all damp penetration.
Testing and Certification
Before any fireplace system is used, it should be properly tested. This includes checking during construction that no obstructions exist in the flue and that mortar hasn’t dropped down to create blockages. Once complete, visual checks and potentially smoke tests should verify proper operation. For gas installations, appropriate certification from Gas Safe Registered installers is mandatory, and homeowners should always ensure they receive and retain these important documents.
What a Snagging Inspection Can Reveal
A professional snagging inspection can identify many visible defects in fireplace and chimney installations, including poor quality masonry work, inadequate or missing flashings, incorrectly positioned terminals, unsecured or poorly fitted fireplace surrounds, and visible gaps or damage that could affect performance. However, it’s important to understand that snagging inspections are not full structural surveys. Inspectors cannot see inside chimneys to verify flue liner installation, confirm that hidden damp-proof courses have been correctly positioned, or assess whether combustion air provision meets regulatory requirements without specialist equipment.
Taking the Next Steps
If you’re buying a new build home with a fireplace, or if you have concerns about an existing installation, understanding these standards is the first step towards ensuring your system is safe and compliant. We’ve created a comprehensive guide that breaks down each section of NHBC Standards Chapter 6.8 in detail, explaining what each requirement means for your home and why it matters.
Read our complete guide to NHBC Standards Chapter 6.8 – Fireplaces, Chimneys and Flues to learn more about specific requirements for solid fuel, gas and liquid fuel installations, understand what documentation you should receive from installers, and discover how to identify potential issues with your fireplace and chimney system.
Whether you’re about to complete on a new build home or you’re already settled in, knowing these standards empowers you to ask the right questions and ensure that one of your home’s most important safety features has been installed correctly. And if you’d like professional assistance in assessing your new build home, our experienced snagging inspectors can help identify visible defects and provide peace of mind about the quality of your new home.