Lisa Stephens of ROCKWOOL UK gives an update on the latest developments in wind load testing to equip buildings for the more extreme winter storms we are seeing.
Across the globe, extreme weather conditions are becoming more common, with heavy flooding, wildfires and hurricanes regularly making the news headlines and heavily impacting towns, cities and communities often with devastating consequences.
Recent research by Newcastle University and the Met Office, looking specifically at the UK, has concluded that climate change may increase the number of extreme winter storms, including strong winds.
Analysing data from climate simulations covering historical (1981-2000) and future (2060-2081) periods, the research showed that “as the climate warms, these events are likely to become more severe, with stronger winds and heavier rainfall happening together.”
The study advised that these changes are mainly driven by increased rainfall, as a ‘thermodynamic’ response to rising temperatures. Additional contributing factors include a strengthened jet stream and its southward displacement that brings storms through warmer areas, leading to further increases in rainfall.
Resilient structures
Wind load (which refers to the forces exerted on a structure by wind), depends on factors like location, building height and surrounding terrain. Urban environments, in particular, are at heightened risk due to the funnelling effect of wind between buildings, which amplifies local wind speeds. Likewise, coastal and high-altitude locations require specific design adaptations to address elevated wind pressures.
Architects have always had to contend with the impact of wind. However, as wind speeds increase due to climate change, so do the loads that buildings must endure. While wind-tunnel testing and computational fluid dynamics (CFD) modelling are commonly used to assess wind loads on buildings during the design phase, identifying areas of high stress and highlighting the impact of building geometry on wind load, analysis of material testing data is also critical.
Tested for site
Rainscreen insulation, often used on high-rise buildings more exposed to extreme weather and wind, must withstand such pressures. Wind-load testing is common for most rainscreen insulation available in the UK and Ireland; however, testing programmes vary in terms of the build up.
Typically, rainscreen insulation is independently tested in accordance with BRE Digest 346 Part 7. This testing regime sees product samples placed and sealed into dynamic wind loading test apparatus and subjected to sequential proportional loading cycles that mimic what a building would experience within a 50-year lifespan. The process tests the insulation prior to the final cladding being added, which, in reality, will give further protection.
To ensure that test scenarios reflect typical construction types, it is important to consider all materials within the build-up and the impact they may have on other materials and the test result. This means examining whether, for example, a
breather membrane was included in the test data available for your choice of rainscreen insulation.
A breather membrane is important to the testing process, as the wind can infiltrate behind it and exert pressure on the insulation. By assessing the insulation and membrane, both installed according to respective manufacturer guidance, the testing process examines and provides architects with the results of a build-up that more closely replicates what is used onsite.
With this in mind, we have recently published test results that assess the performance of our rainscreen insulation with a breather membrane in a minimum of category four hurricane conditions.
Resilient choices
The inclusion of a breather membrane is one way that ‘true-to-site’ testing programmes have been designed to assess wind load performance. Fixing choice has also been explored, acknowledging site practicalities.
In some circumstances, for example, space does not allow the use of a typical 70 mm EJOT fixing on a steel frame cladded facade and as such, a 50 mm option is used. This recent wind load testing programme explored using 50 mm options against category four hurricane conditions to independently verify performance in such site circumstances.
Another test configuration included a masonry facade with the same insulation installed within an ACS channel fixed to a light-gauge steel frame without mechanical fixings. This setup was tested for category five hurricane conditions, again providing independent verification of performance and highlighting possible time and cost savings onsite.
By testing materials in true-to-site configurations, manufacturers can demonstrate that their products meet the specific demands of real-world applications. This level of rigour is fundamental in rainscreen systems, where insulation must contribute to thermal and acoustic performance and resist wind pressure to maintain overall facade stability.
Lisa Stephens is product manager at ROCKWOOL UK