Protecting decorative projecting brickwork

Projecting brickwork is a popular design feature on masonry building envelopes. However, the resulting inconsistent cavity depths can add complexity when ensuring structures’ passive fire protection – Graham Laws of Siderise Insulation explains more, and describes solutions

Masonry finishes have long been a desirable facade choice for all kinds of buildings around the world. Its robust properties and earthy colours lend a sense of safety, solidity and shelter. Aesthetically, beyond the wide range of textures and sizes it offers, brickwork can also be laid offset to create projecting bands or shapes to add interest to large elevations or around windows and doors. However, the inconsistent cavity depth this creates can be a challenge to effectively protect using standard passive fire protection cavity barriers.

Inconsistent cavities
It is a legal requirement in line with BS 9991 for steel-framed masonry constructions with a ventilation cavity to include vertical and horizontal cavity barriers and fire stops, even if the cavity is fully filled with A1 rated (non-combustible) insulation. These are blocks of fire-resistant material that seal the cavity and prevent fire, smoke and heat spreading up the facade and into different building compartments. On a typical build up with a consistent cavity depth, these will be standard full-fill products that are installed between the inner leaf and masonry wall to effectively seal off the cavity.

Cavities that vary in depth are more complex, as a full-fill cavity barrier will be unable to meet the masonry leaf and therefore close the gap. For straightforward applications, it may be possible to simply notch a standard full-fill barrier, so it fills the cavity, or to place a board into the gap to flatten out the irregularity. However, this is more difficult to do for more complex and increasingly popular brickwork patterns. The accepted market solution for projects with uneven inner masonry surfaces or irregular design features is to use an intumescent material.

Intumescent cavity barriers
Often referred to as open state cavity barriers, these passive fire protection products are designed to leave a ventilation gap allowing free vertical movement of air when ventilation is required, or when caused by irregular brickwork patterns. In the event of a fire, the intumescent material in the product will activate at a critical temperature (typically around 130°C) and expand to meet and mould to the face of the outer construction, forming a robust seal across the gap.

Third party testing
As with any fire safety product, it is essential to make sure that any cavity barriers are third-party tested to ensure they are fit for purpose. This includes making sure they have been tested in conjunction with a DPC (damp proof course).

Open state cavity barriers cannot be effectively tested using the standardised tests for typical full-fill products as the time taken for the gap to close could in theory lead to a ‘fail’ even though compartmentation is quickly established and the product performs well. To resolve this, the Association for Specialist Fire Protection (ASFP) outlines the test configurations and failure criteria for testing of ‘Open-State’ Cavity Barriers in their Technical Guidance Document (TGD 19). This is a “small-scale” test, typically using 1.2 m long seals and is a modified version of the standard EN 1366-4:2006 Fire resistance tests for service installations – linear joint seals. Working with a manufacturer’s technical department or fire safety specialist can help you to ascertain which products and tests are most suitable for your application.

Decorative and safe brickwork
Passive fire protection solutions that have been specifically developed and tested for masonry facades can help to ensure that this beloved building material keeps pace with modern construction standards and regulations, remaining synonymous with robust and long-lasting buildings.

Graham Laws is technical director at Siderise Insulation