Belgium’s first post-tensioned thermal break at GO! Zavelberg Primary School

Summary

Delivering strength, speed, and sustainability without compromise 

When GO! Onderwijs set out to create a new school campus on the urban edge of Brussels, their ambition was to deliver bright, flexible learning spaces that connect seamlessly with nature while meeting the highest standards of energy efficiency.

The GO! Zavelberg Primary School brings this vision to life through a compact, three-storey building covering 3,435 m², supporting nursery, kindergarten, and primary education for around 300 pupils. The project represents a vision for modern, sustainable education spaces, combining architectural innovation with environmental focus.

Achieving this vision presented a unique challenge: how to create wide, 11-metre spans within a slim 300 mm slab while maintaining thermal efficiency? 

Overcoming a structural challenge 

Post-tensioning was the ideal structural solution for the project, reducing slab thickness while maintaining strength, minimising material use, and enabling longer spans between supports. However, combining the HIT solution with a post-tensioned slab that included the terraces in the post-tensioning process had never been implemented before.

Until now, balconies on post tensioned concrete frames have typically been constructed using conventionally reinforced concrete. While this is a viable method, designers often faced significant rebar congestion and clashes at the joint between the balcony and the main slab, particularly due to the presence at the same location of the anchor heads required for post-tensioning at the slab edge and the structural thermal breaks.  

By using the Halfen HIT in post-tensioning applications, balconies and the main slab are treated as one area, resulting in multiple benefits:  

• Formwork is installed/removed at the same time and can be re-used on the next level/phase  
• Concrete is poured all at once  
• Simultaneous stressing of the concrete takes place at the balcony edge, rather than at the thermal break location 

Engineering Belgium’s first post-tensioned thermal break  

Democo approached Leviat with a unique challenge to integrate a structural thermal break within a post-tensioned slab, something never previously achieved in Belgium. Working closely with Abetec and Interspan, Leviat applied the Halfen HIT-PT system to meet the project’s specific demands.

Because the Zavelberg terraces were supported rather than cantilevered, the HIT modules had to be rotated upside-down. This adjustment positioned the compression and shear modules closer to the top of the slab to suit the revised load path. Standard HIT transition pieces allowed the post-tensioning ducts to pass cleanly through the 80 mm mineral-wool insulation layer, preserving both structural performance and thermal efficiency.

As this was the first time Halfen HIT had been used in a post-tensioned slab, a detailed layout plan was prepared by Leviat’s design engineers, then carefully reviewed by Leviat R&D department in close collaboration with Interspan. On site, Leviat’s Product Manager and sales engineer provided direct explanations and training to Democo’s installation team. Thanks to this preparation, installation was completed successfully, setting a new benchmark for post-tensioned thermal break solutions. 

Fast, seamless and lasting performance  

On site, the benefits were immediate. Balconies were propped and poured together with the main slab in a single sequence, enabling one concrete pour, one stressing operation. Formwork could be struck once per level and reused efficiently, saving time and resources. 

Key benefits achieved: 

• Balconies included in the post-tensioning process. This simplified construction and reduced project complexity.
• Single pour and stress cycle for balconies and main slab, saving time and improving site efficiency.
• Concrete stressing was carried out at the balcony edge rather than at the thermal break, simplifying the post-tensioning process. 
• Clear concrete flow at balcony connections. This avoided reinforcement congestion and guaranteed better structural quality.
• Faster formwork installation and removal. 
• Full REI 120-rated thermal break across balconies. 
• 11-metre spans achieved with a 300 mm slab thickness. This delivered flexible, open-plan spaces while minimising material use. 

Together, these advantages helped deliver a faster, leaner, and more energy-efficient construction process without compromising the architectural vision. 

A new benchmark  

The GO! Zavelberg Primary School project proves that structural efficiency and high thermal performance can be achieved together, without compromise. With 11-metre clear spans, a slim 300 mm slab, and a fully continuous thermal break, the building delivers strength, speed, and sustainability in one integrated solution.

By rethinking traditional methods and applying the Halfen HIT-PT system, Leviat has opened new opportunities for sustainable, high-performance construction across education, residential, and commercial sectors.