Onyx Multipurpose Building, Sofia - Case Study

BILDA fixing system can be customized to meet any of your project needs. One great example of this feature in action is Onyx, a commercial building of height 30m that is Curtain Wall (CW) glazed with stone pilasters of 30mm thick Granite and Limestone - "portrait" oriented.

The major challenge here was that the substructure - just the floor slabs. Initial design included metal columns being erected between the slabs and the cladding substructure being attached to it. This would mean additional substructure, and more importantly, puncturing the insulation causing excessive thermal bridges.

Project info

Project: ProArch architects Ltd
Facade Engineering: Facade Detail
Cladding Installer: Alumina Elit                Year of Construction: 2022/2023
Product: BILDA Rainscreen System for 30 mm Granite and Limestone cladding

The stone cladding in the Onyx project is mainly pilasters between CW fragments. As, the extreme CW mullions will support only a smaller part of triple glazed IGU units, they have residual bearing capacity to support also the weight of part of the stone cladding elements.

So, a special thermally broken CW integrable profile has been designed for attachment to the respective extreme mullions. Custom brackets that support the BILDA horizontal strut profile are attached to it. Back fixing BILDA clips are attached off-site to the stone elements and hanged onto the horizontal strut profiles.

Additional bracket to support the stone cladding independently are avoided. Puncturing of insulation avoided also. A low-cost, fast to install, and reliable solution achieved.


The unique detailing of the cladding using BILDA bespoke façade elements eliminated the need for additional substructure thereby reducing the material quantity by 30%, while also allowing significant savings in the overall construction process.

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Case Study - Onyx6