What regulations apply to chimney flues?

The height of chimney flues

The height of a chimney flue is defined to ensure efficient smoke evacuation. In fact, the so-called stump (the part of the flue protruding from the roof) must be higher than the ridge of the roof. This requirement is designed to prevent smoke from being forced back into the house, or causing a nuisance to occupants or neighbors. This can be considered an abnormal neighborhood disturbance. According to standard NF DTU 24.1, updated in 2020, the stump must extend at least 40 centimetres above the highest part of the roof. This height can be adjusted according to various parameters, such as the presence of adjacent buildings or climatic conditions. In 2020, this standard added a new criterion for chimney flues for type B boilers (liquid or gaseous fuel appliances operating under pressure). In homes with this type of appliance, the flue pipe must be concentric. It must have 2 flues:

• The central flue, which evacuates the flue gases.
• The second duct, placed around the first duct, draws air from the room and carries it to the combustion chamber.

This double-walled concentric flue provides additional safety, since in the event of a malfunction, the burnt gases are not released into the room, but reintroduced into the appliance.

Distance from neighbors and safety

There are also restrictions on the distance between the chimney flue and neighboring properties. The aim is to reduce the risk of nuisance to neighbors and to prevent potential dangers such as fire. The exact distance varies according to the height of the flue and the location of neighbouring buildings. In general, a flue must be placed at a sufficient distance to prevent fumes from entering neighboring properties or affecting their comfort. For new installations, the standard requires that the flue stump (the visible part above the roof) extends at least 40 cm above the highest point of the roof, as mentioned above. This measure is designed to minimize nuisance to neighbors, and applies to homes within 8 metres of the stump.
It's also crucial to insulate the flue at ceiling penetrations and roof outlets to prevent fire hazards. A gap of at least 8 cm must be maintained between the flue and any combustible material, with certain exceptions permitted for woodwork and flues with special insulation.
When commissioning old flues, a sweep is required prior to lining. The standard also specifies ventilation requirements and recommends the use of flexible casing for inclined masonry ducts.
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