Choosing the right product helps to translate your specification into as-built performance
When specifying rainscreen insulation, architects must consider how designed performance can be affected by real world conditions.
Fire safety regulations mandate non-combustible insulation for certain external wall system build-ups on residential buildings between 11 and 18 metres in height.
The exception is if a full-scale fire test to BS 8414-1 or -2 has been undertaken, but this is only valid if the system is installed to the exact same specification as the test.
What happens on site isn’t always consistent with the design so, to help mitigate fire risk, architects should always specify non-combustible insulation with a Euroclass A1 or A2-s1,d0 reaction-to-fire classification.
In terms of thermal performance, it’s important for U-value calculations to be as accurate as possible. This can be challenging with rainscreen facades, but using detailed 3D U-value calculations, rather than the standard method, helps achieve greater accuracy.
Installation also has an impact on thermal performance - human error, uneven substrates and movement from subsequent work can introduce air gaps that prevent target U-values being met.
Flexible insulation, like rock mineral wool, is easier to install correctly and more forgiving of real-world conditions. It also ‘knits’ together at the joints, minimising gaps and maximising thermal performance.
Once rainscreen insulation is installed, leaving it exposed to weather conditions can also negatively impact performance. For this reason, it should be installed on a rolling front, however a survey suggests that this happens on average less than 50 per cent of the time.
Architects can help to preserve their intended performance by specifying Rocksilk RainScreen Slab EE, which has an enhanced water-repellent facing that reduces the risk of water damage when the insulation is left exposed during construction.
Lastly, for buildings to be genuinely sustainable architects must consider raw materials, manufacturing and transportation, which all impact the embodied carbon of construction products and the building as a whole.
Glass mineral wool has the lowest levels of embodied carbon of any mainstream insulation material in the UK, but a rainscreen facade also needs the performance benefits of rock mineral wool.
That’s why, to achieve the required performance while reducing embodied carbon, the ideal solution is a combination of both materials.
By prioritising non-combustibility, ease of correct installation, embodied carbon reduction and resilience to weathering during construction, architects can specify insulation that supports real-world performance.
Learn more about these topics by taking Knauf Insulation’s RIBA-certified CPD, Specifying Rainscreen Insulation for Real Performance.
For more information and technical support, visit knauf.com
Contact:
technical.uk@knaufinsulation.com