Kevin Gamble of Saint-Gobain Weber explains how steel frame construction with external wall insulation (EWI) can help to increase not only thermal efficiency but internal area when building new homes and extensions.
The shortage of skilled tradespeople to build homes in the traditional way has been a real problem for a number of years, and the situation isn’t going to get better any time soon.
This is one of the reasons we will need to rely on the development of new systems, such as framed construction, to help us address the housing crisis.
Developers, housebuilders and housing associations are starting to realise the benefits of offsite and modern methods of construction – quicker build time, improved build quality, cost savings and less reliance on skilled labour. But until recently, little attention has been paid to the other obvious benefit associated with new methods of construction such as steel frames: more space.
Masonry construction is typically thick, heavy and slow. Several bricklayers, even with years of experience, could take weeks to construct a typical four-bedroom home. And there’s also another important point which needs to be considered. As Building Regulations progress towards the Future Homes Standard in 2025, achieving the required U-values will likely become harder to reach with masonry construction.
Choosing a lightweight steel frame system can reduce the need for hefty foundations – significantly reducing build time and in turn cost. A high quality, prefabricated system can be installed by a less experienced workforce. In addition, constructing with a steel frame is not reliant on good weather, and there are fewer inherent concerns that may exist with a timber frame system for example, such as height limitations or the possibility of shrinkage.
EWI SYSTEMS
Steel frames are a very reliable form of construction and when used with a good EWI system there are huge benefits.
Using an EWI system improves the thermal performance of a building and therefore, the interior comfort. Because EWI is suitable for most building types, it can be used to add insulation to existing brick buildings and enables anyone renovating or upgrading a home to decorate and remodel with whatever finish they require. It can even be finished with a brick slip system to give the appearance of traditional brick but is installed in a fraction of the time.
The whole concept of EWI means it’s ideal for new build structures as it simplifies the wall construction and is very lightweight. And as it delivers great thermal efficiency with much narrower walls, with costs soaring, any gain on internal space is a win-win for both developer and homeowner.
A conventional masonry construction would require a 102 mm brick, 100 mm cavity and 100 mm block. Add to that a 12.5 mm plasterboard and a 3 mm layer of skim and the total depth is around 330 mm. Moreover, the typical insulation material used in the cavity is likely to achieve an unimpressive U-value; typically around 0.3 W/m2K.
Contrast that with the walls at a recent project in the conservation area of Leamington Spa where a dilapidated department store has been extended to create a block of 26 luxury apartments and retail space.
Architect Tate Hindle opted for a steel frame extension and EWI system. The existing walls were of solid concrete and, including EWI, were 485 mm deep and achieved a U-value of 0.18W/m2K. The frame extension with EWI was designed to have an even lower U-value of 0.13W/m2K, with an overall depth of just 364 mm.
This was important for the project as a key goal was to maximise the internal space within the apartments without going beyond the original footprint of the property. For potential homebuyers and tenants any extra space is hugely desirable and for developers and housebuilders, it makes a home more marketable.
Assuming the same parameters for an average detached house with, for example, overall outside dimensions of 5.4 x 8.6 m on plan, using steel could potentially increase the internal floor area by an impressive 14.8%.
To achieve the same thermal performance, a building with typical masonry construction filled with mineral fibre insulation would require a 180 mm wide cavity to achieve the U-value of 0.18W/m2K, thereby reducing the internal floor area as a result of the thicker walls.
On the Leamington Spa project illustrated here, a multi-layer system was specified. The flexibility of EWI meant that on this particular project the perfect colour of finish could be used to ensure the building preserved the town’s historic features, whilst providing modern, thermally efficient and spacious accommodation.
Kevin Gamble is technical and certification manager at Saint-Gobain Weber