What are the typical applications of different building envelope solutions?

This blog post refers to two different building envelope solutions for commercial buildings: insulated panels, featuring PIR insulation, which are factory-produced and delivered to site as completed units ready for installation; and site-assembled systems, featuring glass mineral wool insulation, where the building envelope is constructed on site, in parts.

Generally speaking, where large roofs and elevations need to be weatherproofed, insulated and made airtight to high levels of performance, PIR-insulated-steel faced panels provide a fast and consistent option to achieve those targets.

Site-assembled systems tend to be a slower and a more labour-intensive build, but offer benefits such as better acoustics and flexibility in aesthetics. The elements that make up the system can be offered with individual non-combustible ratings, whereas a PIR panel cannot.

Ultimately, it comes down to which solution achieves the right balance of performance for the use, or uses, of the building – with fire safety having obviously become a particularly significant driver over the last five years or so.

Does site assembly or pre-fabrication impact on fire safety?

When looking at the two cladding options purely in terms of their insulation component, it might seem obvious that an increasingly risk-averse construction industry would opt for the non-combustibility of glass mineral wool over the combustibility of PIR foam.

Such a simplistic view, however, ignores the nature of how the two solutions are built up. As a factory-produced unit, an insulated panel’s pre-fabrication should provide certainty of performance.

Therefore, we should also consider how the declared fire performance of systems is replicated and repeated in the built environment. This and other assessments of envelope system should be considered in a holistic manner and assessed verses the required physics and construction practicalities of the building in question.

Yet we repeatedly find that site-assembled systems are becoming the solution of choice – especially on large logistics projects that may have an element of insurance-backed funding.

What has driven changes in fire safety requirements for building envelopes?

Among many changes made in the aftermath of Grenfell, classifying the reaction to fire of products based on the EN 13501 set of standards, rather than the BS 476 set of standards, banning combustible rated products in high rise multi storey accommodation over 18m, and removing system testing to BS 8414, were the most significant.

Reliance on prescriptive regulation could not only increase the risks associated with poor levels of competence, the prescribed materials would not necessarily work well as part of the overall construction. However, this prescriptive identification has swayed insurers to discourage the use of combustible products in other building types, even though regulation allows it.

For the most part, this has meant assuming the highest level of risk, expecting the best possible standard, and requiring non-combustible components. Such an approach precludes insulated panels featuring PIR insulation.

Architects, specifiers and engineers have since faced substantial rises in their professional indemnity insurance if they select insulated panel products. Yet these are highly efficient products, and this risk-averse approach will have unintended consequences on the cost, speed and efficiency of construction.

Does fire safety testing risk being undermined by insurance requirements?

At Building Systems UK, our concern is that the unwillingness of insurers to acknowledge the certification held by insulated panels will devalue, and potentially undermine, that certification if it is not seen as a useful barometer of system performance.

In the interests of achieving the highest levels of building safety in a fire situation, large scale system testing is a more reliable way of assessing the in-use performance of construction products than the small-scale tests used on individual materials to classify combustibility.

This principle has been borne out through decades of testing PIR-insulated steel-faced products using insurer certified large-scale system tests, such as those developed by the LPCB and FM Approvals. Numerous real fire case studies support the results of those tests and show these products perform to the highest standards within the buildings they are designed for.

A systems approach to construction is key to achieving safe, high-performance buildings. It is detrimental to the construction sector generally if tested and audited performance is ignored in favour of insisting only on non-combustible components where regulation does not call for it.