Boiler flues in high-rise buildings

Gas Safe Register’s Technical Team looks at what the Building (Amendment) Regulations 2018 – often referred to as the “high-rise combustibles ban” – mean for gas engineers.
This article appears in the September-October 2024 issue of the magazine.

In June 2018, the Ministry of Housing, Communities and Local Government (MHCLG) consulted on banning combustible materials within any space forming part of the external walls of relevant high-rise buildings – such as new blocks of flats, hospitals, residential care homes and student accommodation. This followed the Grenfell Tower fire in June 2017.

The subsequent amendment to Building Regulations for England and Wales 2010 was initially applicable only to buildings higher than 18 metres in England but similar restrictions are now in place in Scotland.

The following questions and answers highlight some key points to consider if you are carrying out work such as a boiler installation/replacement in this type of building.

What is a ‘relevant building’?
A relevant building is one with a storey (not including rooftop plant areas or any storey consisting exclusively of plant rooms) at least 18m above ground level and which:
• Contains one or more dwellings
• Contains an institution
• Contains a room for residential purposes (excluding any room in a hostel, hotel or boarding house).

“Above ground level” in relation to a storey means above ground level when measured from the lowest level adjoining the outside of a building to the top of the floor surface of the storey. This includes residential blocks of flats, student accommodation, care homes, sheltered housing, hospitals and dormitories in boarding schools, etc, with a storey above 18m in height, irrespective of the primary purpose of the building.

The regulations apply to the entire building if it includes even a single residential dwelling as well as other uses, such as offices or retail.

Regulations regarding fire spread over the external wall of a building must always be demonstrated. Consideration should be given to the choice of materials used for the external wall, or attachments to the wall, to reduce the risk of fire spread over the wall, including their extent and arrangement.

How do the regulations affect buildings undergoing improvements such as a boiler replacement?
The requirement is that any new building work on such buildings that includes installation of a new or replacement boiler must be carried out so that only materials with a fire-resistance rating of A1 or A2-s1,d0 become part of an external wall or specified attachment, unless covered by one of the exemptions in the regulations.

This had an immediate impact for new condensing boilers being installed soon after the amendment was introduced. Boiler manufacturers have had to develop flues that had a metallic inner flue duct resistant to corrosion from the condensing products of combustion as an alternative to flues with inner ducts made from plastic polypropylene.

What exemptions apply to the installation of a flue?
The exemptions include membranes, seals, gaskets, fixings, sealants and backer rods (see Regulation 7(3)).

External flue weatherproofing collars are likely to be classified as a seal and so exempted under Regulation 7(3). These components are designed to help ensure compliance with other requirement of the Building Regulations, such as those addressing risk of re-entry of products of combustion considered in Approved Document J, and where it is impractical to make good the flue externally due to restrictions of working at height.

If it does not form part of the external wall, then this does not apply because it is not a specified attachment. The same applies to plume management kits.

Note: Compliance with Requirement B4 of Schedule 1 to the Regulations regarding fire spread over the external wall of a building must always be demonstrated. Consideration should be given to the choice of materials (including their extent and arrangement) used for the external wall, or attachments to the wall, to reduce the risk of fire spread over the wall.

You should confirm the use of a plume kit with the appliance manufacturer and/or local building control.

What if a building is being converted from an office to a relevant building?
If the works result in an existing building being converted to a “relevant building”, the materials in the existing wall must comply with the combustibility restrictions throughout the entire building. This will require a review of existing external walls and removal of materials, such as boilers with flues that do not comply.

Does the ban affect condensate discharge pipes?
Yes. A plastic condense pipe cannot pass through the wall for an external waste discharge point.

What about existing boiler flues?
Materials that are already part of the external wall or are existing specified attachments and are not being replaced are not covered by the ban.

Are older boilers with a flue using combustible material in a high-rise property At Risk?
When you are carrying out a service or gas safety check, you should still risk-assess the installation as usual for compliance with the gas safety regulations, manufacturer’s instructions and Normative documents, and follow IGEM/G/11, the Unsafe Situations Procedure, if you find defects.

The Building (Amendment) Regulations do not, on their own, mean that an existing installation is At Risk.

Gas Safe Register recommends that you should read and fully understand the regulation requirements and consult your local building control office if you have any questions.