Fabric first: the economical approach to sustainable construction

As sustainability becomes an ever-growing priority for the construction sector, Ian Clay of SIPS@Clays, a leading UK provider of structural insulated panels, explains why building performance should be our prime concern

With the Zero Carbon policy coming into force soon, there is a lot of work to be done if buildings are to meet the demanding new standards. And while there may now be the potential to offset carbon through off-site allowable solutions schemes, there is a better, more sustainable and more economically viable alternative.

Of course, none of this is to say that carbon offsetting is an ineffective solution for reducing overall emissions. The problem with this scheme is that it allows for a compromise on building performance, with repercussions for the homeowner in terms of both energy bills and maintenance costs.

But it’s not all doom and gloom. The introduction of Target Fabric Energy Efficiency (TFEE) rates indicates a shift away from short-term affordability and towards long-term sustainability. Rather than depending on renewable technologies and carbon offsetting schemes, the homes of the future will most likely be constructed using a fabric first approach.

The prioritisation of building performance over bolt-on technology is a significant step for the construction sector. Under previous guidelines, homes built using traditional methods and materials would have had to rely heavily on renewables in order to provide the required levels of functionality and comfort.

The fabric first approach to construction provides a longer-term solution that can help ease the discrepancy between building quality and cost, minimise the strain on resources and, ultimately, improve modern living standards.

Promoting sustainability, fabric first
Innovative construction technologies such as structural insulated panels (SIPs) can be used to create airtight homes that rely far less on carbon offsetting and renewable add-ons than buildings of traditional construction. Boasting outstanding thermal performance, minimal thermal bridging and low thermal mass, SIPs may be the UK’s biggest step yet towards achieving the Passivhaus standard.

Traditional masonry and timber frame constructions need to work much harder, incorporating a profusion of additional technologies in order to meet the regulations.

Figure 1 demonstrates this by comparing three different scenarios: a masonry construction, a timber frame construction and a SIPs construction with 75mm of rigid urethane insulation. All three of these scenarios emulate a fabric first approach, with heat loss minimised by whatever means necessary to limit reliance on renewables.

While the masonry and timber frame constructions display a high level of thermal performance, they also necessitate a range of additional technologies to compensate for poor airtightness and the effects of thermal bridging. Masonry buildings require parge coats to create a contiguous surface, while all air barriers surrounding openings in timber frame buildings must be lapped and sealed.

By contrast, the inherent jointing arrangement and OSB facing found in SIPs means that they can achieve the required performance with almost no modifications, structural or otherwise. The only add-on device that is fundamental to all SIPs constructions is a mechanical ventilation heat recovery (MVHR) system, to counteract the technology’s unparalleled capacity for airtightness.

As Figure 2 shows, SIPs also offer notable reductions in wall and roof construction width, a huge advantage with space being so limited.

Modern construction technologies such as SIPs offer a long-term solution to the Zero Carbon Policy that is more economically viable than attempting to maintain affordability by building to a lower standard. By focusing on building performance now, construction professionals can rest assured that the new standard is being fulfilled without any compromise on quality.

The Garden House (front elevation)

Figure 1: Example Specification Comparison. All scenarios assume: regular condensing boiler with a room sealed fanned flume (89.5 per cent efficient); weather compensator; A-rated fuel heating pump; no secondary heating; 300 litre hot water cylinder (2.31 kWh/day loss factor); primary pipework fully insulated; 100 per cent low energy lighting Figure 1: Example Specification Comparison. All scenarios assume: regular condensing boiler with a room sealed fanned flume (89.5 per cent efficient); weather compensator; A-rated fuel heating pump; no secondary heating; 300 litre hot water cylinder (2.31 kWh/day loss factor); primary pipework fully insulated; 100 per cent low energy lighting Figure 2: Total Build-Up Thickness Figure 2: Total Build-Up Thickness