Luke Davies, Rock Mineral Wool Product Manager for Knauf Insulation, explains how to streamline the specification process for rainscreen façades, while prioritising real-world performance.

Tightening requirements
The construction industry has seen several updates to Building Regulation guidance over the last few years. This includes changes to Approved Document L and Approved Document B, which raised the standards for thermal performance and fire safety respectively.

The Building Safety Act has also introduced measures that will significantly impact rainscreen specifications. Although the Act applies to all residential properties, there is a particular focus on higher-risk buildings. These are described as buildings over seven storeys or 18-metres tall, that contain at least two residential units, or are used as care homes or hospitals.

The legislation has introduced three new Gateways, or ‘checkpoints’ for the Health and Safety Executive to assess compliance with Building Regulations. This is part of the golden thread of information – a digital record that is required to show how the building was designed and built. Retrospective liability has also been increased to 30 years, so it’s essential that a project’s principal designer is confident in the chosen materials and systems. The level of accountability has increased for architects and throughout the whole supply chain, from design to ongoing maintenance of the finished building.

But a compliant design doesn’t always equate to the same as-built performance. Inaccurate U-value calculations or poor installation can compromise insulation’s thermal and fire safety performance. There is also the possibility that products which have been tested separately might not work together as intended.

So, how can architects design for real-world performance, while removing some of the complexity from the specification process?

U-value accuracy
As-built thermal performance requires U-value calculations that are as accurate as possible. Simplified calculations aren’t recommended for rainscreen façade systems because they apply a blanket correction factor to account for things like penetrations from the steel frame. This can mean inaccurate specification and compromised performance. Instead, architects should request 3D U-value calculations from the insulation manufacturer, which account for the impact of those penetrations more accurately, providing a better indication of as-built performance. To streamline the process, it is also advisable to get a report, detailing the components included in the calculations. This can be passed on to the supply chain, to show how changes to the specification could affect the U-values.

Buildable products
Insulation must be correctly installed, with minimal gaps to deliver its specified thermal and fire safety performance. Unfortunately, some types of insulation are easier to install correctly than others. For example, rigid boards won’t sit flush against a cavity unless it is perfectly uniform and flat. Mineral wool insulation on the other hand, is flexible, allowing it to maintain close contact with the substrate. Where slabs meet the ends also ‘knit’ together. This inherent buildability makes mineral wool insulation easier to install correctly, minimising gaps and maximising thermal performance.

System specifications
Specifiers need to be confident that individual products will work together as designed and when it comes to fire safety, there is no room for doubt. One way to help mitigate this risk, is to specify a full system solution. These are systems that include cavity barriers, sheathing insulation, and fixings, which have been tested both individually and together. A good example is the range of Rocksilk RainScreen Cavity Systems, recently launched by Knauf Insulation. They each feature insulation with a Euroclass A1 reaction to fire classification, making them suitable for every height and use of building. The systems also include open state cavity barriers with an intumescent strip, a closed state cavity barrier, and additions to the innovative Rocksilk RainScreen FFCB range. Systems like these allow architects to specify a solution that best meets their fire performance requirements, confident it has been tested to the relevant standards.

As the industry continues to evolve and regulations tighten further, product choice will face even greater scrutiny. System solutions will help to streamline the specification process and architects will need to prioritise full system testing, accurate calculations, and buildable products, to deliver performance that matches up to their designs.

Contact Details
Please click here to learn about Rocksilk RainScreen Cavity Systems.