Why do I need a preliminary design?

ETICS: Focus on service – Part 3

During the planning phase, a preliminary design is made to test the general suitability of the product for the intended application and to carry out an initial check of the load-bearing capacity. In the area of external thermal insulation composite systems, this is often the case with statically or safety-relevant mounting elements for the fastening of attachments. The preliminary design does not replace a static dimensioning but provides a basis for a first calculation of quantities and costs.

But what exactly is a preliminary design and what needs to be taken into account?

In our current article, we provide you with the relevant details. What is preliminary design and what is its purpose? A preliminary design or pre-dimensioning is, in simple words, a first check if the intended product is suitable for the planned application. Specifically, it is tested, among other things, whether the load-bearing capacity of the product can withstand the impact resulting from the application, for example from wind.
Die geplante Position des Anbauteils hat einen Einfluss auf die Tragfähigkeit und muss daher für eine Vormessung bekannt sein.

The planned position of the attachment has an impact on the load-bearing capacity and must thus be known for a preliminary design.

This might be relevant, for example, when fastening railings – so-called French balconies – in front of floor-to-ceiling windows. In addition to the loads from their own weight and wind, the railings are also subject to other variable forces such as the impact or vertical load. These occur, for example, when someone bumps against or leans on the railing. Since these are safety-relevant areas, it is particularly important to thoroughly determine the suitability of the products. Furthermore, the selection of the right fastening system for the substrate of the application can only be made with a dimensioning.

For the greening of ETICS facades, the possible installation grid also depends on the type of plant, or the plant must be selected accordingly depending on the planned installation grid.

Another case is the facade greening with EJOT Iso-Bar ECO. This is also an attachment that is subsequently mounted on the external thermal insulation composite system. In addition to the loads resulting from own weight and wind, the weight of the chosen greening, for example, plays an important role. For optimal preliminary design, it should therefore be known exactly which plant will later be used for the greening. Since this application is a distance installation, the system thickness (adhesive, insulation material, etc.) is also an important input variable.

Even if products are basically intended for an application, the respective boundary conditions on a building always determine the final suitability in a specific case. Therefore, a static dimensioning must always be carried out when using statically and/or safety-relevant components.

When verifying the preliminary design, the load-bearing capacity is evaluated, amongst other things. The effect of the loads described above must not exceed the load-bearing capacity of the product. These load-bearing capacities are specified in the respective approval of the product. This also shows why only products with national building authorities’ approval or European Technical Approval may be used for statically and/or safety-relevant areas. When using products without these approvals, the required verification is not possible. Preliminary design is carried out on the basis of  "acknowledged rules of technology", such as approvals and standards, and must always be done by an expert.

Furthermore, it is important to define which requirements are to be met by the component that is intended for the application before the dimensioning. Variable values such as weight and dimension of the attachment, acting loads and also substrate conditions have an influence on the suitability of the product for the respective application. However, factors such as the location and height of the building or the system structure are also relevant.

Difference between preliminary design and static dimensioning

The biggest and most important difference between a premliminary design and a static dimensioning is that although the preliminary design is the basis for an initial quantity and cost calculation, it is not a reliable proof in terms of building law for which liability is assumed. It serves as a first orientation and is thus rather a recommendation. The final static dimensioning must always be carried out by a planning and/or structural engineering office that is authorised to present building documents.

Performance by EJOT?

Our Service for you:

EJOT offers preliminary design as a service – also especially for mounting elements for attachments, such as EJOT Iso-Corner, EJOT Iso-Bar and EJOT Iso-Bar ECO for facade greening. All relevant data are gathered in an uncomplicated and efficient way via a questionnaire.

With the preliminary design, you receive verification of the load-bearing capacity based on your individual pre-planning as well as the estimated required quantity which may be helpful when preparing your offer.
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Read also the previous part of the series and learn more about our 360° service on the topic of ETIC systems.