There are many types of insulation on the market. The most commonly used in rainscreen applications are phenolic boards or mineral fibre slabs. These are installed directly onto the masonry, cross-laminated timber (CLT) or steel framing system, sitting behind the rainscreen facade itself to provide thermal performance, acoustic benefits and weatherproofing when installed alongside a vapour control barrier.

One key difference between these products is their thermal conductivity (lambda value). The lower this value, the more efficient the insulation is at preventing heat loss from conduction. This means that the desired U-value can be reached with a thinner thickness of insulation. Phenolic boards used in rainscreen applications can have a thermal conductivity as low as 0.021 W/mK. In comparison, rock mineral fibre insulation materials typically have a thermal conductivity of around 0.034 W/mK. This means that a much thicker and heavier construction is typically required when using rock mineral fibre which can impact not only the speed and ease of build, but also the internal dimensions of the space.

On the other hand, rock mineral fibre insulation solutions typically have improved acoustic properties and are often rated as either A1 or A2 for reaction to fire under the European Classifications (also known as Euroclass). This rating is based on the suite of tests outlined within BS EN 13501-1. This rating will determine the suitability of materials to be used for certain building types or heights as explained in the next section. 

Learn more about rainscreen facades.

To simplify the process of building up these external layers, Kingspan has also developed rainscreen substructures. These are essentially internal panelised facade systems, combining an insulation layer with factory-applied weather seal (FAWS), internal liner sheet and external weather sheet in a single product. The rainscreen finishes can then simply be installed over the top, whether in a direct fix or ventilated arrangement. This allows the internal layer of the rainscreen system to be completed much faster than standard approaches, enabling the building to be made weathertight and the internal works to begin whilst the cladding is finished externally. These are available with both mineral fibre(Eurobond Rainspan panel) and our self-blended advanced closed-cell insulation technology (QuadCore Karrier.) 

The QuadCore insulation used in the QuadCore Karrier Wall Panel has a thermal conductivity of 0.018 W/m.K, supporting slim constructions with no compromise on thermal performance, whilst the K-Roc Karrier Panel has a European Classification of A2 – s1, d0 in accordance with EN 13501-1, making it suitable for use on certain buildings where a better reaction to fire criteria needs to be met (see next section).

How do I know which insulation type is the most appropriate for my rainscreen facade system?

The insulation product choice will ultimately be dictated by the project requirements, such as targeted wall U-values or acoustic performance, desired wall thickness, or installation limitations or a tight project timeframe. However, it is crucial that the chosen product is made from an insulation material permissible under the local Building Regulations for the type of building it is to be installed on. 

Below is a brief summary of the regulations*: 

England, Wales and Northern Ireland

Approved Document B: Fire Safety (ADB) under B4 External fire spread Regulation 7 (England and Wales) and Technical Booklet B: Materials and workmanship Section 2 (Northern Ireland) all state that the external walls of ‘relevant buildings’ over 18 metres must be constructed with materials achieving a European Class A1 or A2-s1, d0 rating (i.e. be non-combustible or of limited combustibility) in accordance with BS EN 13501-1. However, the definition of what constitutes a ‘relevant building’ differs in the regions. 

The original definition applied in all regions when the regulation was introduced in 2018 was that a ‘relevant building’ was one with a storey at least 18 m above ground level (not including roof-top plant areas or any storey consisting exclusively of plant rooms), which contain one or more dwellings, an institution, or a room for residential purposes. This includes sheltered housing, student accommodation, care homes, hospitals, boarding school dormitories, hotels, hostels, and boarding houses. 

Both Wales and Northern Ireland are currently still working with the older definition (hotels, hostels, and boarding houses not included), but we can expect these regions will follow England in tightening these standards.

The government has also announced new statutory guidance to restrict the combustibility of materials used in and on the external walls of residential buildings, between 11-18m in height. To be deemed compliant, either the external surfaces of external walls and materials should be class A2-s1, d0 or better or meet the performance criteria given in BRE report BR 135 for external walls using full-scale test data from BS8414-1 or BS 8414-2. This gives designers more flexibility to use lower performing but more environmentally positive materials on lower risk buildings without comprising safety.

Scotland 

The Scottish regulations are more stringent. Technical Handbook Section 2: Fire for domestic and non-domestic buildings states that the external walls on all buildings with a storey at a height of more than 11 m, and certain assembly, entertainment, hospital, and residential care buildings below 11 m (Clause 2.7.1) must be constructed using Euroclass A1 or A2 rated materials

Creative and compliant facades

Whilst rainscreen facade systems provide incredible design flexibility, it is vital that architects and facade engineers ensure that both the external finishes and the insulation solutions they choose not only achieve their design aims but that they are also compliant with the regulations applicable to their project. 

Still unsure which insulation material or product would be best suited to your project? Get in touch with our expert technical team.

*Accurate at the time of publishing. Please always refer to the local government websites for the most up-to-date versions of the Building Regulations and to check for any updates that may be relevant to your project.