Anyone planning a rear-ventilated façade needs a reliable foundation. A pull-out test on the façade shows that, how load-bearing the existing substrate actually is, thereby laying the foundations for a safe and cost-effective façade structure. For this article, we spoke to our expert from SAGER, Dominic Rieder. In the interview, he explains why the pull-out test is much more than just a technical assessment on site and what really matters in practice.

Dominic, what exactly is a pull-out test, and why is it carried out on a building site?

A pull-out test determines the load-bearing capacity of the existing substrate. It thus provides the basis for the structural assessment of a façade assembly. A pull-out test is essential, particularly for masonry. The results are used to determine the maximum spacing between brackets and profiles. From this, material requirements can be calculated and the substructure system can be specifically optimised. In this way, the pull-out test not only contributes to structural safety but also to cost-effective planning.

Why is this issue so important when it comes to façades and fixings?

Because a pull-out test provides clarity at an early stage. Once we know what loads are permissible in the specific subsoil, we can specify the distances between brackets and profiles precisely, draw up the bill of materials accurately and tailor the substructure to the project. At the same time, U-value requirements can be better met using the maximum substructure grids and calculated in advance. This is precisely why a pull-out test not only ensures structural safety but also cost certainty.

What information is needed in advance to ensure that an escape attempt can be properly prepared?

Thorough preparation is crucial. First, we clarify the basic questions: What needs to be fixed in place? Where is the building located? What is the nature of the subsoil? What U-value needs to be achieved? Which substructure system is planned? Which anchoring method will be chosen? And is a structural analysis report required? These points form the basis for everything that follows.

In addition, there are other factors relevant to the project. We examine whether the building is in a prominent location, whether the hydrostatic pressure at the site is known, how tall the building is, and whether compliance with the Minergie standard or a U-value certification is required. The façade cladding, its weight, any secondary structures and the type of fixing – whether visible or concealed – also influence the subsequent planning.

What role does the subsoil play in practice?

A very significant one. Not all substrates are the same. Even within the same building, different qualities of masonry may be present. In addition, the finish of the substrate also plays a role, for example joints, steps, transitions or expansion joints. At the same time, we need to know where fixing is strictly prohibited, for example in riser zones, around recesses, in areas subject to fire safety requirements or where seismic reinforcement has been fitted.

This is precisely why standard assumptions are often insufficient in practice. We need to assess the actual subsoil conditions so that subsequent planning is based on reliable data. The SFHF/IFD Guideline on Tolerances for Curtain Wall Facades points out that sub-base tolerances must be taken into account during planning and execution, and that the substructure must be adapted accordingly.

What do we look out for when it comes to fixings and edge clearances?

The choice of anchoring method must always be suited to the substrate and the structure. Key factors include whether the anchoring is to be carried out in concrete or masonry, what anchoring depths are possible, and which bracket or fixing system is to be used. The edge distances are equally important. The standard edge distances are 2x the dowel insertion depth for masonry and 1.5x the dowel insertion depth for concrete.

Other factors relevant to the planning process include the profile spacing, the bracket spacing and the profile overhang. These values have a direct impact on the substructure and on the quantity of materials required.

How does an on-site breakaway test work?

On site, at least ten boreholes are drilled at various points across the building. These borehole locations are numbered, photographed and thoroughly documented. We then enter the measured values into our calculation tool. This yields the final value for the permissible load in the existing subsoil.

What is interesting is that differences can even be found within the same building. Variations in the quality of the masonry also lead to different tensile loads. This is precisely why it is so important to inspect the actual substrate at the site and not simply rely on assumptions.

How do pull-out tests help to optimise the substructure?

The results are incorporated directly into the subsequent planning. They help us to determine whether a Minergie standard or a specific U-value is specified, whether U-value verification is required, how the insulation thickness affects the structural analysis of the brackets, and how the number of brackets can be optimised in such a way as to also improve the U-value.

We also examine which substructure system has been selected, whether the installation is horizontal or vertical, what method of cladding fixation is intended, and whether different types of cladding are used on a single façade surface. All this information is used to create a bespoke substructure for the specific project.

What results do planners and contractors receive in the end?

Depending on the project, various documents may be produced as a result. These include a structural analysis report, if required, an anchor test report, details of the maximum permissible spacing, and a bracket and profile grid on façade plans. This means that the pull-out test does not end with the measurements taken on site, but serves as a reliable basis for planning, tendering and execution.

Conclusion

A pull-out test provides clarity at an early stage. It reveals the actual load-bearing capacity of the existing substrate and helps to plan anchors, the substructure, the grid system and the use of materials on a project-specific basis. Particularly in the case of rear-ventilated façades, it is therefore far more than just a technical assessment. It lays the foundation for safe, cost-effective and precisely coordinated solutions and supports both structural and economic planning.

If you are planning a rear-ventilated façade or carrying out a pull-out test, you can contact our team of experts I’d be happy to help.