The importance of through wall fire testing

Light gauge galvanised steel framing systems (SFS) are primarily used for wall constructions, such as infill walling, continuous walling, high bay walling and loadbearing structures in low to medium rise situations.

Their light weight and versatility deliver benefits to the entire construction team, providing the designer, developer and end client with cost-efficient, sustainable design solutions for a wide variety of residential, hotel, student accommodation, social housing, healthcare and education projects.

Whilst efficiency, versatility and sustainability are desirable attributes for any building system, they count for little without certified proof of the system’s ability to meet the required technical performance standards in the areas of acoustics, thermal efficiency, loadbearing and, most importantly, fire protection.

With steel framing systems, fire performance and thermal efficiency are achieved through the combination of materials that are used in conjunction with SFS to construct the wall. For external wall constructions, from inside to out, this would typically consist of dry lining, SFS (possibly including insulation within), sheathing board and insulation. The final wall construction can vary according to the external façade materials that are used, which can range from brickwork to insulated render, timber cladding, composite panels, ventilated rainscreen and many others that might be selected to achieve the desired exterior finish or budget.

Traditionally, performance of the wall construction could be assessed by compiling the technical data from manufacturers of each of the materials used in the construction; boards, sheathing, SFS and insulation. Whilst building materials manufacturers were confident that their products would work within a system of suitable products, since Grenfell, there has been increasing recognition amongst SFS manufacturers of the need to undertake fire testing of the wall construction itself to provide a ‘through wall’ performance, providing designers and contractors with added assurance of a solution’s performance capabilities.

Whilst there is currently no strict definition of what ‘through wall’ means, it is widely regarded as the part of the wall that provides the majority of the fire, thermal and acoustic properties, most commonly the zone from the inside face of the internal dry lining to the outside face of either the sheathing board or insulation.

The reason for this ‘through wall’ concept is that, with so many exterior façade materials available, it would be impossible to test every possible wall construction. The ‘through wall’ approach to performance allows manufacturers to test a meaningful number of material combinations (SFS, internal and external boards plus insulation). The tested solutions will either be from the dry lining through to the sheathing board or from the dry lining to external insulation.

This approach provides the design team with the freedom to choose the desired external façade, provided, of course, that the necessary performance requirements are met.

Building regulations set out requirements for time performance, particularly with regard to integrity (passage of smoke and flame), insulation (temperature on the opposite side of the wall) and load bearing capacity where the wall is being used in a structural capacity.

In order to achieve ‘through wall’ fire performance data, SFS manufacturers construct different complete wall build-ups measuring 3m x 3m, comprising light gauge steel frames fitted with various combinations of boards and insulation materials to UKAS-accredited laboratories for testing.

Each build-up is tested using a large scale, high heat test (reaching up to 600 degrees Centigrade in 5 minutes), which measures the performance of the whole wall by simulating fire trying to break out through a solid wall. Tests are conducted to British Standards BS EN 1364-1 and BS 476-22 (for non-loadbearing walls) to achieve the 120-minute, 60-minute and 30-minute fire ratings typically required by building regulations.

In most cases, fire performance is an inside to out requirement, aiming to prevent the spread of fire from its source to adjacent compartments. However, where buildings are in close proximity to each other fire resistance will also be required from outside to in.

Whatever the circumstances, through wall fire testing and the performance data it returns for the combinations of materials used in wall constructions is a positive step forward from SFS manufacturers. As more manufacturers commit to this approach, the array of certified wall constructions available to designers will increase (at Metsec, we currently offer more than 400 configurations), providing greater choice and flexibility in the solutions they can use, not only to meet fire performance requirements but also to achieve other performance criteria, such as thermal and acoustic insulation, as well as satisfying aesthetic and budgetary needs.

Steering a way through the specification process will always be simplified by early engagement with the SFS manufacturer’s design teams, which can bring knowledge and experience to the table to achieve the most time and cost-efficient ways to achieve performance and design objectives.

Added assurance in the performance and quality of the solution will be gained from manufacturers’ product and design warranties.