Why Fire Detailing

In November 2018 changes to the Building Regulations were made as a result of a catastrophic fire. The fire at Grenfell Tower brought into question the regulatory control over the construction of external walls. This led to the Building Regulations being updated to stop the use of combustible material in the external walls of residential buildings over 11m in height. The guidance given in Approved Document B: volume 2 (ADBv2) was also updated to reflect this change.

A further change was made to ADBv1 and 2 in 2020 to reduce the height limit for the requirement of sprinklers to be installed in new homes, from 30m to 11m. However, the control of material in the external wall of a new home less than 11m high and constructed of two leaves of masonry has not changed. Due to the inherent fire resistance of clay bricks and concrete blocks, it is still allowable to use combustible materials within masonry cavity walls.

Building Regulations

This simple guide to the current requirements of the Building Regulations is also a reminder of what has been recognised for centuries, namely that masonry buildings are inherently robust for energy efficiency, fire resistance and sound insulation. Masonry buildings are by their nature and materials resistant to fire.

The designer or specifier should remember that this fundamental quality leads to simpler detailing and construction and this simplicity in turn benefits the thermal and acoustic detailing as well as the construction.

2437_Fire Guide_Homes below 11m-MAUVE-V18

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Masonry is an excellent material for a ‘fabric first’ approach and its longevity and local production brings embodied carbon benefits. When compared with frame constructions, masonry buildings generally have fewer layers and fewer materials performing separate functions within the wall build-up. However, all buildings contain cavities and some concealed spaces where fire can spread undetected.

To minimize the dangers of undetected fires the Building Regulations generally require that cavities are provided with barriers to reduce the extent of void spaces and to contain any spread of fire and smoke.

The requirements for masonry buildings are far less onerous than for framed constructions. This guide explains the simple measures that are required to comply with the Building Regulations for detailing cavity barriers and in particular Section 5 Internal fire spread – dwellinghouses & Section 8: Cavities - flats (concealed spaces) of Approved Document B Volume 1.

Why Fire Detailing

Building Regulations

Construction Fire Details

E1: Insulated steel lintel

E2 01: Independent concrete lintel

E2 02: External steel lintel

E3: Cill

E3: Cill full height window - Option 1

E3: Cill full height window - Option 2

E4: Jamb

E7: Concrete intermediate ﬂoor

E7: Concrete intermediate ﬂoor (section 2)

E10: Pitched roof eaves insulation at ceiling level

E11: Pitched roof eaves insulation between rafters

E13: Pitched roof gable

E10: Parapet roof junction - ‘L’ parapet post

E10: Parapet roof junction - ‘C’ parapet post

E18: Masonry separating wall

E25: Masonry staggered separating wall

S1a: Vertical services penetration