Tweet

Architects designing rainscreen façades are under immense pressure to deliver buildings that are efficient, safe and stand up to scrutiny. With a slew of new regulations, third party stipulations for increased fire safety, and common site issues threatening the final performance, these projects feel burdened with risk. Rainscreen specification is changing at an unprecedented pace, and many architects feel they are struggling to hit a moving target.

Insulation plays a huge role in the purpose and performance of rainscreen façades and designers need a new approach to specification, one that prioritises actual performance in the finished construction and ensures the build-up is futureproof against tightening regulations.

How specification is changing

Building Regulation guidance has changed dramatically in the last few years, with stricter requirements for energy efficiency and safety. Updates to Part L include tighter limiting U-values for the building fabric and require a 31% reduction in operational CO₂ emissions compared to past regulations.

These changes were made in anticipation of the incoming Future Homes Standard, which is expected to ask for a further reduction in emissions of 75-80% compared with 2013 regulations. This means that architects need to consider ways to ensure high thermal efficiency that not only meets regulations now but will satisfy future requirements.

Regulations have also increased in complexity, with the Building Safety Act (BSA) now requiring that all buildings pass through three ‘gateways’ during the planning, design and finished construction stages to get certified as fit for use and occupation. This puts much of the responsibility for the performance of the building in the hands of the architect.

Adding to this complexity are the requirements of third parties involved in the construction process. For example, Approved Document B requires non-combustible materials to be used in certain external wall system build-ups, such as rainscreen façades, on all residential buildings between 11m and 18m. The only exception is if a full-scale fire test to BS 8414 has been conducted. But many third parties, including architects, local authorities and insurers, have already introduced blanket non-combustibility policies.

These regulatory reforms amount to sweeping changes across the construction industry. For architects specifying rainscreen insulation, it means an increased burden of responsibility and scrutiny. To manage these requirements, specifiers should consider using non-combustible materials such as mineral wool in every rainscreen façade project and consider how the buildability of the material might impact the end result.

Damaging exposure

As well as compliance challenges, architects working on rainscreen façade projects must consider potential performance risks presented on site. For example, best practice for mineral wool insulation in rainscreen façades is to use a ‘rolling front’ approach, working in smaller sections to first install the insulation and then cover it with the outer panel. Prolonged exposure to wind and rain can compromise mineral wool’s performance.

Unfortunately, survey data indicates that the ‘rolling front’ is only achieved approximately half the time due to scheduling issues. In 70% of cases, the sheathing insulation is left exposed for over a week [1] – enough time for weather conditions to cause damage and compromise performance.

Given stringent regulatory requirements for energy efficiency and fire safety, and the requirement for the building to perform as designed to pass through all three gateways of the BSA, weather damage presents a serious risk to the completion of any rainscreen façade.

Other installation trials can also threaten the performance of the finished façade. Rigid board insulation, for example, can be particularly awkward as it won’t sit flush against a cavity unless it is perfectly uniform and flat. Boards also need to be precisely cut and taped, all of which can introduce air gaps that compromise thermal and fire safety performance.

How specifiers can reduce installation risks

While responsibility for a successful installation sits in large part with the contractor, it is clear from the data that it’s all too easy for factors outside of anyone’s control to play a part in delays and installation issues. The solution is to specify products that are resilient to prolonged weathering and are easier to install correctly, to give contractors flexibility if things don’t go precisely to plan on site.

Rocksilk^® RainScreen Slab EE, for example, is the UK’s first non-combustible rainscreen sheathing insulation with an enhanced water-repellent facing, making it resilient to weathering. It is made primarily from mineral wool, which is flexible and maintains close contact with the substrate, while abutting edges ‘knit’ together to minimise air gaps and maximise thermal performance.

Specification for the real world

The specification of rainscreen insulation must align with the practical realities of onsite conditions to ensure optimal performance and regulatory compliance. By adopting more robust solutions like non-combustible mineral wool products with weather-resilient properties, specifiers can help mitigate risks, enhance safety, and ensure the long-term success of rainscreen façade projects.

[1]  Survey of rainscreen installers by RCI magazine, conducted 2023. Sample size 10.