Understanding the standards that govern fireplaces, chimneys and flues in your new build home is essential for ensuring safety and proper functionality. The NHBC Standards Chapter 6.8 provides comprehensive guidance on these installations, covering everything from design and construction to testing and maintenance requirements.
6.8.1 Compliance
All fireplaces, chimneys and flues in new build homes must comply with NHBC Technical Requirements and relevant Building Regulations. Working fireplaces should be designed to ensure efficient operation of the appliance, provide an adequate supply of combustion air, and protect the building fabric from fire risk. Preformed chimneys (decorative chimneys manufactured off-site) must hold satisfactory assessments from appropriate independent technical approvals authorities acceptable to NHBC.
The design must ensure proper fire separation, appropriate hearth construction, continuous flue paths from hearth to outside air, and correctly positioned terminals and outlets. Good workmanship and effective supervision during construction are essential, as even well-designed systems can fail if poorly installed. A professional snagging inspection can help identify visible defects in fireplace installations, though it’s important to note that such inspections are not full structural surveys and may not identify hidden issues within chimney structures.
6.8.2 Provision of Information
Clear and comprehensive design information must be provided to site supervisors, specialist subcontractors and suppliers before work begins. This should include the position and size of hearths, fireplaces, chimneys and flues, the proximity of combustible materials, terminal positions, DPC and flashing details, and construction specifications for fireplace openings and chimney connections.
Crucially, documentation should specify the limitations on the type of appliance or open fire that can be installed and the fuel that can be used. It should also detail which tests are required on chimneys and flues and who is responsible for carrying them out. Without this information readily available on site, there’s a significant risk of incorrect installation, which could compromise both safety and functionality.
6.8.3 Solid Fuel – Fireplaces and Hearths
Fireplaces and hearths for solid fuel appliances must be constructed to safely accommodate the fire or appliance for which they’re designed. Constructional hearths should be provided in accordance with Building Regulations and manufacturer’s recommendations. Where appliances are not provided initially, it’s essential to construct fireplaces and hearths suitable for the appliance most likely to be fitted in future.
Recesses for open fires or closed combustion appliances should comply with Building Regulations and be lined with a fire back or fire bricks. Walls near appliances and their hearths must be positioned to minimise fire risk. During a snagging inspection, visible aspects of hearth construction and fireplace recesses can be checked, though the inspector cannot assess hidden structural elements or confirm compliance with all technical specifications without invasive testing.
6.8.4 Solid Fuel – Combustion Air
An adequate supply of combustion air is a statutory requirement for solid fuel appliances. The air supply should come from external air, either directly or indirectly, and must comply with Building Regulations and the manufacturer’s recommendations. Insufficient combustion air can lead to dangerous situations, including poor fuel combustion, excessive smoke production, and the potential for carbon monoxide build-up.
The specific ventilation requirements vary depending on the type and size of the appliance, and full details are contained in the relevant Building Regulations for your area. Homeowners should never block or restrict ventilation openings that have been provided for combustion appliances.
6.8.5 Solid Fuel – Flue Pipes
Flue pipes connecting solid fuel appliances to chimneys must be correctly designed for safe operation. They should have a cross-section equal to the outlet of the appliance they serve and should not be inclined more than 45 degrees from vertical. This ensures that combustion gases can flow efficiently up and out of the property.
Flue pipes must be adequately separated from combustible materials in accordance with Building Regulations. This separation is critical for fire safety, as flue pipes can become extremely hot during operation. Any deviation from these requirements could create a serious fire hazard.
6.8.6 Solid Fuel – Chimneys
Chimneys for solid fuel appliances must incorporate flues capable of safely conducting products of combustion to external air. The structure must support the flue lining and provide adequate protection to adjacent structures. Flues should not serve more than one appliance and must be of sufficient cross-section to remove all combustion gases.
Combustible materials close to brickwork or blockwork chimneys must be adequately separated, and for timber frame construction, full separation details should be included in the design. Materials used for chimneys should be capable of resisting fluctuating temperatures up to 1,100°C. Factory-made insulated chimneys should be designed to specific standards and have a minimum operating life of 30 years.
Flue liners are essential components that should have rebated or socketed joints installed with the socket facing upward. They must be non-combustible, properly jointed with mortar, and reasonably smooth on the inside. The space between liners and brickwork should be filled with weak insulating concrete unless the manufacturer recommends an alternative.
6.8.7 Solid Fuel – Outlets and Terminals
Outlets and terminals must be adequately separated from combustible materials and other parts of the home, enable satisfactory discharge of flue gases, and prevent damp ingress. The flue functions more effectively when the outlet is in a low-pressure zone, typically on the sheltered side and at the ridge of a pitched roof or close to the windward side of a flat roof.
Terminals should be purpose-made components, built into the top of the masonry to a minimum of 125mm or 0.25 times the length of the terminal (whichever is greater), and sealed to the flue liner. An acceptable terminal can be achieved where the top flue liner projects a minimum of 20mm above the chimney capping.
Chimney cappings should be weathered, monolithic slabs designed to protect the masonry below, with a drip at least 30mm from the chimney face to shed water clear of the masonry. Where cappings are designed as cover slabs supported on piers, the height of supporting piers must allow a free opening equivalent to at least twice the area of the flue outlet.
6.8.8 Gas – Fireplaces and Hearths
Gas fireplaces and hearths must safely accommodate the appliance for which they’re designed. All gas appliances should be fitted by a Gas Safe Registered installer holding the relevant competencies for the work, and installations must comply with the Gas Safety (Installation and Use) Regulations 1998. This is a legal requirement, not merely guidance.
Combustible materials close to any chimney or flue should be adequately separated according to Building Regulations and manufacturers’ instructions. The provision of hearths and recesses should also comply with Building Regulations. For solid fuel effect gas appliances, hearths and recesses should follow the requirements for solid fuel appliances, provided the appliance has been tested by an approved authority.
For all gas appliances, hearths should be marked at the edges to provide a warning to homeowners and discourage combustible floor finishes (such as carpet) from being laid too close to the appliance. This can be achieved by introducing a change in level.
6.8.9 Gas – Combustion Air
Like solid fuel appliances, gas appliances require an adequate supply of combustion air from external air, either directly or indirectly. This must comply with statutory requirements, manufacturer’s recommendations, Building Regulations and BS 5440-2. The specific ventilation requirements depend on the type and rating of the gas appliance.
Inadequate combustion air is a serious safety issue that can lead to incomplete combustion and potentially dangerous carbon monoxide production. Homeowners should never block ventilation grilles or openings that have been installed to provide combustion air.
6.8.10 Gas – Flue Pipes
Gas flue pipes must safely connect an appliance to a chimney, or a flue to a terminal. They should not have adjustable draught controls and must have a free area at least the same size as the outlet of the appliance. Unlike solid fuel flue pipes, gas flue pipes should not be horizontal (except for balanced flues).
Flue pipes should be fixed according to manufacturer’s recommendations, fixed socket up where appropriate, and correctly aligned. Where flue pipes are long, they require support directly below each socket with a maximum spacing of 1.8 metres. When connecting flue pipes to flue blocks and ridge terminals, proprietary connectors should be used. Combustible materials must be adequately separated from flue pipes in accordance with Building Regulations and manufacturers’ instructions.
6.8.11 Gas – Chimneys
Chimneys for gas appliances must incorporate flues capable of safely conducting products of combustion from the appliance to external air, whilst supporting the flue and protecting adjacent materials. Importantly, chimneys for gas appliances must not incorporate an adjustable draught control, which distinguishes them from solid fuel installations.
Flue blocks for gas appliances should comply with BS EN 1858 (concrete) or BS EN 1806 (clay), and rigid metal flue liners and chimneys should meet BS EN 1856 standards. Flexible flue liners are not acceptable in new build properties. For masonry chimneys, flues should follow the same requirements as those for solid fuel appliances regarding liner installation and jointing.
Gas flue block chimneys can only be used for certain types of gas appliances and must have a minimum performance class of FB4 N2. These blocks should be constructed, jointed and weatherproofed according to design specifications and manufacturer’s instructions, and correctly bonded to the flanking masonry. Gas flue blocks are at least 140mm wide, and where this exceeds the wall leaf width, the extra thickness must be accommodated through specific construction methods, including the use of vertical damp-proof membranes and non-combustible insulation.
Flue blocks should not be built into separating walls unless adequate sound resistance can be demonstrated, and they should not be plastered directly. Instead, a plasterboard lining with an air space or non-combustible insulation behind it should be provided. Factory-made insulated chimneys should be assembled, erected, anchored and protected strictly in accordance with manufacturer’s instructions.
6.8.12 Gas – Outlets and Terminals
Gas appliance outlets and terminals must be adequately separated from combustible materials and other parts of the home, whilst preventing damp ingress. Terminal guards should be fitted over all gas flue terminals where persons could come into contact with them or where they could be damaged. BS 5440-1 advises that terminals less than 2 metres above ground, balconies, or accessible flat roofs should be guarded in the absence of specific manufacturer guidance.
Precautions should be taken to prevent damp penetration, following the requirements for solid fuel appliances regarding frost attack and weathering. All flues that bridge the cavity of an external wall should incorporate a means of preventing moisture crossing the cavity, such as a moisture drip collar positioned in the centre of the cavity. For timber frame construction, specific guidance in IGE/UP/7 should be adopted to maintain the integrity of the vapour control layer.
Where cavity trays and weepholes are used, they should comply with the standards set out in Chapter 6.1 for external masonry walls. During a snagging inspection, the visible positioning and condition of terminals can be checked, though the inspector cannot verify hidden moisture prevention measures within wall cavities.
6.8.13 Liquid Fuel – Fireplaces and Hearths
Fireplaces and hearths for liquid fuel appliances (such as oil-fired boilers or cookers) must safely accommodate the appliance and be suitably separated from combustible materials. The requirements vary depending on the operating temperature of the appliance. Where the hearth temperature below the appliance is likely to exceed 100°C, or the temperature is unknown, precautions should follow the requirements for solid fuel appliances.
However, where the appliance is unlikely to have temperatures exceeding 100°C, it may stand on a rigid, non-combustible imperforate sheet of material without requiring a full constructional hearth. This makes the requirements potentially less onerous than for solid fuel installations. Where appliances are likely to have back or side temperatures exceeding 100°C, hearths and shielding should comply with the requirements for gas appliances.
The temperature characteristics of the specific appliance being installed are therefore crucial in determining the appropriate hearth construction, and homeowners should ensure that the correct specification has been followed for their particular installation.
6.8.14 Liquid Fuel – Combustion Air
Liquid fuel appliances require an adequate supply of combustion air from external air, either directly or indirectly, to comply with statutory requirements and manufacturer’s recommendations. The full details of ventilation requirements for all types of liquid fuel appliances are contained in the relevant Building Regulations.
As with solid fuel and gas appliances, adequate combustion air is essential for safe and efficient operation. Insufficient air supply can lead to incomplete combustion, reduced efficiency and potentially dangerous situations. Homeowners should never obstruct or block ventilation openings that have been provided for combustion appliances.
6.8.15 Liquid Fuel – Flue Pipes
Flue pipes for liquid fuel appliances must safely connect the appliance to a chimney. They should have a free area at least the same size as the outlet of the appliance and be installed in accordance with Building Regulations and manufacturers’ instructions. This ensures that combustion gases can be efficiently evacuated from the property.
The specific requirements for flue pipe installation depend on the type of liquid fuel appliance and the temperatures it generates during operation. Proper installation and adequate separation from combustible materials are essential for both safety and performance.
6.8.16 Liquid Fuel – Chimneys
Chimneys for liquid fuel appliances must incorporate flues capable of safely conducting products of combustion to external air. The structure must support the flue lining and provide adequate protection to adjacent materials. The design must address stability, size and direction, separation from adjacent spaces and combustible materials, appropriate flue liners, and resistance to frost, chemical attack and weather.
Flue pipes should have a free area at least equal to the appliance outlet and, if serving open-flued appliances, should be vertical where possible (or not more than 45 degrees from vertical where this is unavoidable). Factory-made metal insulated chimneys should be designed to specific standards, have a minimum operating life of 30 years, and be installed according to manufacturer’s instructions.
The temperature of the flue gases determines which standards apply. For flue gases unlikely to exceed 250°C, the requirements follow those for gas flue pipes. Where flue gases are likely to exceed 250°C or the temperature is unknown, the requirements follow those for solid fuel. Flexible flue liners are not acceptable for new build properties. The chimney must also have adequate resistance to frost attack (following solid fuel requirements) and weather (following solid fuel requirements).
6.8.17 Liquid Fuel – Outlets and Terminals
Outlets and terminals for liquid fuel appliances must be adequately separated from combustible materials and other parts of the home. Balanced flue terminals should be positioned to allow free intake of air to the appliance, which is essential for proper operation and safety.
Where terminals are of masonry construction, they should comply with the requirements for solid fuel appliances. Otherwise, they should be installed in accordance with manufacturer’s recommendations. This ensures that combustion gases are safely discharged whilst preventing the ingress of rain, debris or other obstructions that could compromise the system’s operation.
6.8.18 All – Fireplaces and Hearths
Regardless of the fuel type, all fireplaces and hearths must safely accommodate the appliances for which they’re designed. A critical safety requirement is that combustible material should not be placed under a constructional hearth unless it is used to support the edges of the hearth, is at least 250mm from the top of the hearth, or is separated from the underside of the hearth by an air space of at least 50mm.
Fireplace recesses should be constructed of solid non-combustible material, with dimensions based on a 125mm concrete hearth below an open fire. The space between a fire back and the masonry forming the recess should be filled with vermiculite concrete (mixed at a ratio of 1:4 lime to vermiculite with water). These requirements apply universally, whether the installation uses solid fuel, gas or liquid fuel.
During a professional snagging inspection, the visible construction of fireplace recesses and hearths can be assessed, including checking for appropriate materials and dimensions. However, inspectors cannot verify what materials lie beneath hearths or within wall constructions without invasive investigation.
6.8.19 All – Fireplace Surrounds
Fireplace surrounds and their fixings must be designed, specified and installed to ensure adequate in-service performance and durability. This is particularly important as fireplace surrounds can be substantial in size and weight, and inadequate fixing can create a serious safety hazard, particularly where there is risk of overturning.
The fixing and support should safely accommodate the proposed type of fireplace surround, taking into account the material it’s manufactured from, its configuration, size and weight, the potential for overturning, and the type of supporting walls and floors. Fixings should generally be of stainless steel to BS EN ISO 3506-1 and specified to provide suitable strength and durability.
Critically, methods that rely solely on adhesive for fixing fireplace surrounds to the structure are not acceptable. Mechanical fixings are required. Fireplace surrounds should be installed by competent operatives strictly in accordance with manufacturer’s recommendations and fixing specifications. The walls and floors of the building must be capable of safely accommodating the additional load.
During a snagging inspection, the visible condition of fireplace surround installation can be checked, including whether surrounds appear securely fixed and properly aligned. However, the inspector cannot verify the adequacy of hidden fixings or load-bearing calculations without access to design specifications. More information on natural and artificial stone fireplace surrounds can be found in the Stone Federation Great Britain Fireplace Surrounds Data sheet.
6.8.20 All – Flue Pipes
Flue pipes and terminals must be suitable for their purpose and provide unrestricted passage for combustion gases between the fireplace or appliance and the outlet. The connection between a fireplace or appliance and the flue should be correctly constructed, with specific details provided in the standards for different connection types, including throat unit connections to lintels, chimney joints to connecting flue pipes, and socketed flue pipes (which should be installed socket up).
Where the bottom of the flue is not directly over an appliance, it should be provided with a means of access for cleaning and inspection, such as a soot box. Adjustable flue draught control units are not permitted where gas burning appliances are installed, though adjustable throat units may be specified for other fuel types and should be fitted according to manufacturer’s instructions.
Flue pipes should be jointed in accordance with manufacturer’s instructions, fixed socket up, and correctly aligned. Different materials are acceptable for flue pipes, including metal flue pipes complying with BS EN 1856, cast iron to the same standard, mild steel (minimum 3mm wall thickness), stainless steel (minimum 1mm thick in specified grades), and vitreous enamelled flue pipes. The choice of material should be appropriate for the fuel type and operating temperatures of the appliance.
6.8.21 All – Flue Liners
Flue liners must be unaffected by flue gases and suitable for their purpose, regardless of the fuel type being used. To produce a suitable flue path, appropriate components should be selected to keep cutting and joints to a minimum. At changes in direction, including bends, offsets and tees, purpose-made components should be used rather than cutting standard liner sections.
Flue liners should be clay or purpose-made concrete as specified in the design, handled carefully to prevent chipping or cracking, and installed according to manufacturer’s instructions. They must be sealed at their joint with the starter block or throat unit, with no cavity formed between the linings and starter elements. Liners should be placed with the sockets or rebate ends facing upwards to prevent leakage of combustion products.
Liners suitable for solid fuel appliances (and generally suitable for other fuels) include those meeting the designation T450 N2 D 3 as described in BS EN 1443, such as clay flue liners with rebates or sockets meeting class A1 N2 or A1 N1 requirements, concrete flue liners meeting specific type classifications, or other products independently assessed in accordance with Technical Requirement R3. Alternatively, imperforate clay pipes with sockets as described in BS 65:1991 are acceptable.
Joints should be made using fire cement or refractory mortar in accordance with manufacturer’s recommendations, fully filled with surplus material cleared from the inside of each joint as the flue is built. The spaces between the lining and surrounding masonry should be filled with weak insulating concrete or the manufacturer’s specified material. Ordinary concrete should not be used for this purpose as it lacks the necessary insulating properties and can cause damage through differential expansion.
6.8.22 All – Flues
Flue pipes should be separated from combustible materials in accordance with relevant Building Regulations and manufacturers’ instructions. This separation is critical for fire safety, as flues can reach very high temperatures during operation. Metal fixings in contact with combustible materials should be a minimum of 50mm from the flue, though this requirement does not apply to floorboards, skirting, dado or picture rails, mantel shelves or architraves.
Twin wall flue systems, which provide enhanced insulation and safety, should comply with BS EN 1856 or be assessed in accordance with Technical Requirement R3. These systems are increasingly common in modern installations as they offer improved performance and can often be installed with reduced clearances to combustible materials.
During a snagging inspection, the visible routing of flues and their separation from combustible materials can be assessed, though inspectors cannot verify hidden clearances within wall or floor constructions. Proper documentation showing compliance with Building Regulations should be available from the builder or installer.
6.8.23 All – Chimneys
Chimneys must provide fire protective casing for flues and be capable of adequately supporting the flue liner whilst resisting damp penetration and the products of combustion. This section covers construction requirements, typical construction details, damp penetration and weatherproofing, and coring and drying procedures.
Masonry chimneys should be properly bonded to or supported by the adjoining walls of the building. Foundations to a chimney should be the same depth as adjacent wall foundations, designed to avoid uneven settlement, and where the chimney forms part of the wall, be a minimum of 100mm wider than the chimney base. Inadequate foundations can lead to settlement and cracking, potentially compromising the integrity of the flue.
The height of an unrestrained chimney should not exceed 4.5 times the smallest dimension on plan of the chimney (where masonry density is at least 1,500kg/m³), or should be designed by an engineer in accordance with Technical Requirement R5. This ensures adequate stability against wind loading and other forces. Chimneys constructed of block, brick or stone should have a minimum wall thickness of 100mm (excluding lining thickness), with specific requirements for chimneys in cavity separating walls and compartment walls.
Masonry below roof level may be constructed using the same bricks and mortar as the general brickwork, but masonry above roof level should be frost resistant unless protected by a projecting capping. In Scotland, frost-resistant bricks should be used for all facing brickwork. Hollow or cellular blocks should be suitable for chimney construction and filled with concrete as work proceeds.
Regarding damp penetration and weatherproofing, where chimneys exit close to the ridge of a pitched roof, occasional damp penetration may occur below roof level. In these situations, the roof space should be well ventilated and any dampness should not reach living areas. Where chimneys exit close to the eaves or through a flat roof, trays and flashings should be installed to prevent all damp penetration. DPCs, flashings and gutters should be provided at the intersection of the chimney with the roof surface.
For coring and drying, where a core (such as a sack of loose straw) is used to prevent mortar dropping into the flue liner during construction, the builder should ensure it is removed on completion. A chimney should be allowed to dry naturally for a minimum period of 14 days before use, as premature use can cause damage through steam generation within the masonry.
6.8.24 Masonry
Masonry used in chimney construction must be capable of supporting intended loads and have appropriate resistance to the adverse effects of frost and sulfates. Masonry materials, including bricks, blocks, stone and reconstructed stone, should comply with BS 6461 or BS EN 15287-1 and BS EN 771. These standards ensure that materials have been tested and proven suitable for their intended purpose.
Where clay bricks are used in external chimney stacks, they should have a durability rating of F2,S1 (as described in BS EN 771) or be protected by a projecting capping of at least 50mm. This rating indicates that the bricks have adequate frost resistance for exposed conditions. Where blocks are used, they should have a minimum density of 1,500kg/m³ unless designed by an engineer in accordance with Technical Requirement R5.
In Scotland, more stringent requirements apply with frost-resistant bricks required for all external facing brickwork, and 100mm blocks used for chimney construction must have a minimum density of 1,500kg/m³. These regional variations reflect the harsher weather conditions experienced in Scotland. A snagging inspection can identify the visible quality of masonry work, including pointing and alignment, though determining compliance with density and frost resistance ratings would require documentation or testing.
6.8.25 Mortar
Mortar used in chimney construction must be batched and mixed to achieve adequate strength and durability. Mortar should be in accordance with Chapter 6.1 External Masonry Walls and include sulfate-resisting cement where flue gases are liable to affect the masonry, such as above roof level.
Sulfate-resisting cement is particularly important in chimney construction because flue gases can contain sulfates that, in the presence of moisture, can cause sulfate attack on ordinary Portland cement. This chemical reaction causes the mortar to expand and disintegrate, potentially leading to structural failure of the chimney. The use of appropriate cement type is therefore a critical specification that should be verified during construction.
The mortar mix should provide adequate strength to support the chimney structure whilst remaining sufficiently permeable to allow moisture vapour to escape. Excessively strong mortars can be counterproductive, as they may be less permeable and more prone to cracking than weaker, more flexible mixes.
6.8.26 DPC
Materials used for damp proofing must adequately resist the passage of moisture into the building. The standards specify several acceptable materials for use as damp-proof courses in chimney construction, each with specific properties suited to different applications.
Acceptable DPC materials include bitumen to BS 6398, polyethylene to BS 6515 (though this should not be used in the chimney stack above roof level where higher temperatures may be encountered), and proprietary materials that have been assessed in accordance with Technical Requirement R3. The choice of material should be appropriate for its location and the conditions it will face.
DPCs in chimneys serve the critical function of preventing moisture from penetrating downwards through the masonry into the interior of the building. They must be carefully positioned and properly integrated with flashings to create a continuous barrier. During a snagging inspection, the visible presence and positioning of DPCs where they meet flashings can be checked, though verifying that DPCs have been installed at all required levels within the chimney structure would require construction stage inspections or documentation review.
6.8.27 Flashings
Flashings and trays must be capable of adequately resisting the entry of moisture into the building. These are critical components at the junction between the chimney and the roof, where water penetration is a common problem if detailing is inadequate.
Suitable materials for flashings and trays include milled sheet lead with a minimum thickness of 1.8mm (code blue or Code 4) complying with BS EN 12588, zinc alloy complying with BS EN 988 and 0.6mm thick, and proprietary materials assessed in accordance with Technical Requirement R3. Lead remains the most common and traditional material for chimney flashings due to its durability, flexibility and ease of working.
Flashings should be made from compatible non-ferrous metal to prevent galvanic corrosion. Lead trays should be bitumen coated where they come into contact with cement, as the alkalinity of cement can corrode lead over time. Proper installation is essential, with flashings typically comprising several elements including apron flashings at the front, stepped flashings at the sides, and back gutter flashings at the rear of the chimney. In areas of severe and very severe exposure, specific detailing requirements apply to ensure weathertightness.
6.8.28 Terminals
Flue terminals must be suitable for their purpose and assist the functioning of the flue. The standards address both draught improvement and chimney capping requirements. Terminals should be purpose-made or formed by extending the flue lining a minimum of 20mm above the head of the chimney, embedded at least 125mm into the chimney (excluding any flaunching) or 0.25 times the length of the terminal (whichever is greater), and have the same cross-sectional area as the flue.
For solid fuel applications, the minimum terminal diameter requirement is 200mm. The terminal of a masonry flue should be jointed to the flue lining with cement mortar to form a seal, preventing combustion gases from escaping through the gap between the liner and the chimney structure.
Where downdraughts may occur, terminals designed to increase updraught should be fitted. However, it’s important to understand that a terminal will not overcome problems caused by the chimney being located in a high-pressure zone. In such cases, consultation with the Solid Fuel Association or other authoritative body may be necessary.
Where a chimney is to be capped, a single unjointed concrete or stone capping should be used. It should project and be throated to cast water away from the face of the chimney, with a drip at least 30mm from the sides of the chimney. Decorative brick cappings should be carefully constructed to avoid rain penetration and frost damage, using frost-resistant bricks where required. During a snagging inspection, the visible condition of terminals and cappings can be assessed, including checking for appropriate overhang, drips and the condition of flaunching or pointing.
6.8.29 Flue Testing
All installations must be tested before use to ensure they function correctly and safely. Flues should be checked during construction to ensure there are no obstructions and that mortar or other blockages are removed. These checks should occur progressively as the chimney is built, as it becomes much more difficult to identify and clear obstructions once construction is complete.
When the flue is complete, a visual check should be made and any obstructions cleared. This final inspection is critical, as even small obstructions can significantly impair flue performance and potentially create dangerous situations where combustion gases cannot escape properly. In some cases, smoke tests may be performed to verify that the flue draws correctly and that there are no leaks in the system.
A professional snagging inspection typically occurs after construction is complete, so the inspector may not have witnessed the progressive testing during construction. However, the inspector can recommend that appropriate tests be carried out if there are concerns about flue performance, or request documentation showing that required tests were completed. It’s important to note that snagging inspections are not full structural surveys and cannot verify the internal condition of flues without specialist equipment.
6.8.30 Further Information
The standards document concludes with an extensive list of relevant British Standards and other technical references that provide detailed guidance on specific aspects of fireplace, chimney and flue construction. These include standards covering metal chimneys (BS EN 1856 series), chimney design and installation (BS EN 15287 series), masonry units (BS EN 771), gas appliance installation (BS 5871, BS 5440 series), and many others.
For homeowners, the most important point is that all work on fireplaces, chimneys and flues should be carried out by competent professionals who are familiar with these standards and requirements. For gas appliances, this means Gas Safe Registered installers with the relevant competencies. For solid fuel and oil installations, appropriately qualified heating engineers should be employed.
If you have concerns about your fireplace, chimney or flue installation in your new build home, a professional snagging inspection can identify visible defects and areas of concern. However, for detailed assessment of compliance with all technical requirements, particularly hidden elements of construction, you may need specialist surveys or testing. Always retain all documentation provided by installers, including installation certificates, warranty information and manufacturer’s instructions, as these will be important for future maintenance and any potential warranty claims.
Understanding these standards helps you appreciate the complexity and importance of proper fireplace and chimney installation. Whether you’re planning to use your fireplace regularly or only occasionally, ensuring it has been constructed to the correct standards is essential for your safety and the long-term integrity of your home.
The Role of Snagging Inspections for Fireplaces, Chimneys and Flues
A professional snagging inspection can be valuable in identifying visible defects and potential issues with fireplace, chimney and flue installations in your new build home. During an inspection, a qualified inspector can assess the visible aspects of hearth construction, check that fireplaces and surrounds appear properly installed and securely fixed, examine the condition of terminals and cappings where accessible, verify that adequate separation appears to exist between flues and combustible materials in visible areas, and identify obvious defects such as damaged brickwork, poor pointing, missing or inadequate flashings, or incorrectly positioned terminals.
However, it’s crucial to understand that snagging inspections are not full structural surveys and have significant limitations when it comes to fireplace and chimney installations. Inspectors cannot verify the internal condition of flues without specialist equipment, confirm that hidden elements such as flue liners, insulation or damp-proof courses have been correctly installed, assess whether combustion air provision meets regulatory requirements, determine compliance with detailed technical specifications without invasive testing, or verify that installations have been completed by appropriately qualified professionals (such as Gas Safe Registered installers for gas appliances).
For these reasons, whilst a snagging inspection provides a useful overview and can identify obvious defects that should be rectified by your builder, you should also ensure that you receive and retain all relevant certification for your fireplace installation, including Gas Safe certificates for gas appliances, building control completion certificates, and manufacturer warranties and installation instructions.
If you have specific concerns about the safety or compliance of your fireplace, chimney or flue system, you may need to commission specialist surveys or testing beyond the scope of a standard snagging inspection.
