The demand for increasing levels of thermal performance is driven by both the market and regulatory pressures and can be answered by innovations in Structural Framing Systems (SFS) technology, writes Knauf
The advantages of SFS methods of construction in terms of speed and efficiency on-site are well-established; but the latest contemporary systems are taking this even further with advances that offer far greater levels of insulation without sacrificing usable space. ‘Through the wall’ building facade systems incorporate insulation within the frame itself and can provide a range of U-values from 0.32 to 0.15W/m2K depending on the materials and thicknesses used.
In conventional systems, insulation is applied externally and so adds to the thickness of the walls, decreasing the amount of usable space within. ‘Through the wall’ SFS avoids this problem through placing the insulation in the frame itself so that it is sandwiched between gypsum-based sheathing boards and the internal plasterboard lining.
Clever thermal stud designs reduce thermal transfer through the steel by offsetting rows of slots which effectively interrupt the conduction of heat through the metal, creating a far longer path for the heat to travel that results in far greater thermal efficiency.
To allow for different thermal, acoustic and structural requirements, the steel framework and the insulation is supplied in three different thicknesses – 100mm, 145mm and 195mm. Even greater thermal performance is possible using an additional layer of earthwool on the inside of the building. Sandwiched between two layers of liner, the interior insulation is available in 45mm, 70mm and 95mm thicknesses and can boost U-values up to 0.15 W/m²K. 
The benefits of the system are not simply in terms of thermal performance – health and safety is improved because it reduces the amount of time operatives have to work outside at height. Once the sheathing boards are attached to the steel frame the building is weathertight and the insulation is fitted from the inside – there is no need to crane up the insulation as there would be in other systems. Using a proprietary ‘through the wall’ SFS also means there is a single source of supply, a full system design and on-site assessment, complete with a system warranty.
Any number of different architectural finishes can also be accommodated. A ventilation channel, fixed on top of the gypsum sheathing board, allows for 25mm and 50mm ventilation cavities to be created for residential applications. From there the finishing possibilities are endless. In the case of render, a carrier exterior cement board is fixed to the ventilation channel as a base for direct render application. Tiles, bricks, glass, timber and metal rain-screening are also easy to achieve, with the cladding material fixed or tied to the facade with suitable fixings secured directly back into the stud.
Similarly, leading proprietary ‘through the wall’ SFS can achieve exceptional U-values of 0.15W/m²K in practice, so meeting the thermal performance proposed for as standard for new-build in the Building Regulations 2016. And accommodate wind-loadings of more than 1.0kN/m² and, for example, carry the deadload of terracotta rainscreen.
Such excellent thermal performance can also be realised without complicating the installation. When an architect is looking for a very low U-value, this would traditionally be achieved with a standard metal framing and then insulation built up the on the outside of the studs. The beauty of ‘through the wall’ SFS is that it is possible to meet the U-value required without the need for any additional external insulation, which can sometimes interfere with the supportwork required for the finishes or cause condensation.
Another big plus is that this also provides a 90-minute fire resistance that would otherwise mean the installation of dense products such as mineral wool insulation or cement particle board.
Ultimately, such an SFS design specification can be chosen over alternative SIPS and traditional SFS systems because it can meet all performance specifications for structural, thermal, fire and acoustic levels and remain competitively priced. It is lightweight, flexible in design, and can accommodate a number of differing external finishes without compromising its core performance levels.
By David Mote