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Caracal Engineering Project

St Andrews

Project Problem

We were tasked with developing a solution that would maximise the amount of PV penetration on the building’s roof, whilst considering the building services and various other challenges that the roof posed.


  • There were several internal parapet walls around the roof to hide some of the services, including the air conditioning units
  • Limited fixation possibilities to the roof slab as a the result of the prevalence of the services and the walls
  • Waterproofing is always of concern when dealing with concrete roof slabs. However, there was no other way of fixing and securing the proposed structure without some form of penetration into the slab
  • We also had to consider the maintenance of the services and the waterproofing
  • The building is 8 storeys up, so the forces acting on the table are considerably higher than if it were a ground mount. This required a detailed engineering investigation to ensure we have the relevant codes met.
  • The logistics effort of getting the components to the roof was substantial. They cannot be carried to the roof because they are too large.

Project Solution

Caracal had to think creatively for this project to overcome the challenges previously mentioned. We have a broad product portfolio, so we were able to tap into it and use components that we apply to carport and ground mount solutions.

The cleanest way to solve the problems posed, especially with the internal parapet walls and the ongoing maintenance of the plant, was to go above it. So, we had to elevate the system. Of course, this increases the strain on the material and the number of fixations to the roof. But there was little choice, so we proceeded with the elevation.

Caracal’s engineers spent a great deal of time considering the fundamental inputs of the design, namely:

  • Ridge height above ground
  • Return period
  • Base wind speed
  • Fixation method

Additionally, we engaged the client on the number of modules they were looking to implement and whether this was possible.

Fixations are fundamental to any system. Without a comprehensive and reliable solution, any product advocated would fail. Unsurprisingly, we spent much time on this aspect. We worked with our supplier, Hilti, on the fixations. It is customary for Caracal to work with experts in their respective fields to give customers greater reliability and quality. In this case, Hilti are the experts. They, in conjunction with Caracal, considered the loads, developed a solution, selected the appropriate chemical fixation, including gauge, grade and chemicals to fulfil the demands of the site.

Additionally, to mitigate and in effect eliminate water ingress that would potentially be caused by drilling into the concrete slab, we worked with another expert in the field – ABE. The company specialises in waterproofing solutions. Again, with much dialogue, we were able to deploy the best product for the purpose.

We had to reduce the number of times we drilled into the roof in order to mitigate potential water ingress. This impacted material selection.

The fewer the fixations, the greater the spans distances. And the greater the spans, the larger the sections need to be, all the while considering the logistics effort of getting the material to the roof and the constructability once it was up there.

We settled on the use of some of our ground mount and carport components as they were light, more easily available and capable of handling the rigors of the application. This meant we could assemble the system much the same way as we do on the ground up on the roof.

The components and modules needed to be craned to the roof, so we were mindful of the lengths of members as well as the weight. Not that the crane would be unable to handle these elements, but there were severe space limitations on the roof, as well as loading considerations.