Lisa Stephens, Product Manager at ROCKWOOL® UK, explores the latest developments in wind load testing in the face of more extreme winter storms
Extreme weather is becoming increasingly common, with heavy flooding, wildfires, and hurricanes devastating urban centres globally.
In the UK, research by Newcastle University and the Met Office predicts an increase in storm severity¹. This highlights the growing importance of designing and constructing buildings to withstand stronger wind loads, using products tested under conditions similar to those found on site.
Understanding wind load pressures
Wind load refers to the forces exerted on a building by moving air. These pressures vary, depending on a structure’s height, location, and surroundings. High-rise buildings, especially in urban areas, are particularly susceptible to them, because of the amplification of wind speeds caused by the funnelling effect between structures.
Traditionally, architects use wind modelling to inform building design. As this modelling is based on a completed structure, it does not necessarily take into consideration the effect that wind load pressures have on exposed materials during the construction phases. That’s why rainscreen insulation, which is commonly used on taller, more exposed buildings, should be wind load tested.
Reflecting site conditions
Many rainscreen insulation products are tested in line with BRE Digest 346 Part 7, which simulates the kind of wind loading a building may face over a 50-year lifespan.
In the testing regime, product samples are sealed into a dynamic wind loading test apparatus and subjected to sequential proportional loading cycles that mimic these 50 years of wind exposure. The process tests the insulation before the final cladding is installed – which, in reality, will give further protection.
However, not all testing is reflective of site practices. For example, a rainscreen system may often incorporate a breather membrane, but this is not always included in wind testing. As wind pressure can act on the membrane and exert pressure on the insulation, omitting it means testing cannot replicate on-site performance.
Likewise, on-site space constraints sometimes limit fixing sizes. While a 70mm EJOT fixing is recommended for installing insulation, it is not always possible. When interpreting test results, it’s important to examine whether the data accurately reflects manufacturer installation guidance and site practices.
Putting NyRock® Rainscreen 032 to the test
To reflect what happens on site, ROCKWOOL has conducted independently verified wind load testing of NyRock Rainscreen 032 across common façade build-up scenarios.
Firstly, it tested a steel frame cladded façade with a breather membrane and 50mm EJOT fixings, replicating a frequent substitution where 70mm isn’t feasible. A masonry façade configuration, again with a breather membrane, was also tested with the insulation fitted in an ACS channel system fixed to a light-gauge steel frame, but without mechanical fixings.
Wind pressures were benchmarked against the Saffir-Simpson Hurricane Wind Scale, used globally to classify hurricanes. The tests exposed the build-ups to pressure levels replicating either Category 4 or Category 5 hurricane conditions, the two highest classifications on the scale.
The findings showed that the steel frame build-up successfully resisted Category 4 hurricane wind loads, while the masonry façade build-up withstood pressures equivalent to a Category 5 hurricane and wind speeds of up to 180mph.
As weather risks continue to grow, choosing products tested in representative build-ups and proven under high wind pressures will be important in delivering resilient, future-ready façades.
For more information, visit: rockwool.link/PBC-SEP25
1. Weather and Climate Extremes, 2023
*Please note that this is a commercial profile.
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