Building Envelopes Competence Centre, Lucerne University

An insight into façade testing

Modern, energy-efficient and sustainable façades are among the most complex and cost-intensive components of any building. Due to the interplay of different requirements, manufacturing structurally sound façades comes with enormous risk. Andreas Luible, Head of the Building Envelopes Competence Centre, explains why – in addition to expert planning – façade testing is an absolute must.

From an environmental perspective, energy-efficient buildings only work if there is complete coordination between all the components, including the façade, and if the specified performance requirements are met. The enormous financial risk of an inadequately designed or executed façade is often underestimated. For example, too much air permeability and the façade can completely destroy the energy concept of a building; while a façade that is not fully watertight can result in considerable damage to the fabric of the building, and an insufficient load-bearing capacity can result in injury or even fatality.

It is for this reason that the legislation around construction products in Europe and Switzerland stipulates that anyone who markets windows or façades must submit a "declaration of performance" stating the properties of the product.
The essential features required of windows and curtain walls , the regulation of which pertains to product standards SN EN 14351-1 and SN EN 13830, include: resistance to wind load, water tightness, air permeability, heat transfer coefficient and total energy transmittance.

Nowadays, calculations can be used to demonstrate thermal insulation or energy transmittance. However, when it comes to air permeability and wa-ter-tightness, it is imperative that what’s known as "type testing" is carried out through an accredited test centre, as these specific quality and performance requirements can only be verified by subjecting the component to rigorous tests.

University-owned façade test centre

The Building Envelope Competence Centre (CCGH) at Lucerne University’s School of Engineering and Architecture (HSLU T&A) is one such accredited test laboratory and has been offering these tests in the university’s very own façade test centre since 2008. The tests can also be carried out at the client’s own test facilities, under the supervision of the competence centre.

The university’s test centre is one of the most cutting-edge facilities in Europe and has the capacity to test façades of up to eight metres wide and twelve metres high. It consists of a sealed test chamber – which can be adapted to fit any size of façade and allows the tester to apply pressures of up to 10 kPa – as well as a sprinkler unit fitted with water nozzles to simulate heavy rain.
In 2019, all the lab equipment was replaced with control and measurement technology that has been specially developed by the Lucerne University of Applied Sciences. In particular, the inaccurate vane ane-mometers were replaced with hot-wire anemometers, which are much more accurate for measuring the rate of air loss at lower flow speeds. Moreover, the university developed its own control software and a control algorithm that uses a high sampling rate to adapt to the loss of the respective test specimen, thus providing a fast and reliable approach to testing different pressures.

Multi-stage testing

The test procedure specified in the product standards is similar for both curtain walls and windows, and consists of the following sub-tests:

1. Air permeability
2. Water tightness
3. Wind load resistance – serviceability
4. Air permeability – repeated test
5. Water tightness – repeated test
6. Wind load resistance – structural safety

In the air permeability test, the relative air loss is measured under a gradually increasing negative or positive pressure in the test chamber. The measured air loss must not exceed the limit specified in the required air permeability class.

In the test for water tightness, the façade or window is sprayed continuously with a defined quantity of water, as the negative pressure in the test chamber is gradually increased. The level of water tightness is determined according to the maximum amount of negative pressure that can be applied before the water starts to permeate the façade.

The wind load test is used to check for any potential deformation of the façade in response to the design wind load, as well as to establish the structural safety of the façade under increased wind loads (1.5 times the design wind load). Any permanent damage to frame elements, components, brackets or anchors under increased wind load is considered a fail, as is any shifting of the seals or edges of the glass supports.

Benefits for students and industry

As well as testing windows and façades, the CCGH supports the façade industry in many other issues relating to the serviceability and structural safety of building envelopes. Among the most important of these are glass testing (e.g. pendulum impact tests or residual load capacity tests for glazed components), mechanical testing of components (such as joints, brackets and anchors), façade testing using thermal and energy simulations, light simulations and measurement, as well as fogging tests on closed cavity façades (CCF).
One of the main groups to benefit from these cutting-edge testing facilities, and indeed from all the research and development activities at the competence centre, are the students on the Civil Engineering course. This course, which specialises in building envelopes, is the only one of its kind in Switzerland and Europe and is producing the future experts in the field.
Prof. Dr. Andreas Luible is Head of the Building Envelopes Competence Centre and is responsible for the Building Envelopes course at the Lucerne University of Applied Sciences. He studied civil engineering at the Technical University of Munich and received his doctorate in 2004 from the EPF de Lausanne. He then worked as a senior façade engineer for the international companies Schmidlin Fassaden Technologie AG, Josef Gartner Switzerland AG and YUANDA Europe Ltd. His research focuses on the dimensioning of glass, new façade technologies and materials, the development of energy-efficient building envelopes and adaptive building envelopes.

Picture Copyright: Building Envelopes Competence Centre, Lucerne University