The Hertogenpark residential block in Antwerp by architect Walter Bresseleers dates from the early 1980s. It comprises 16-storey flats of various types. The ground-floor plinth houses offices and two underground floors.

The façade is executed with a cladding in white marble in which recurrent pathologies are visible, essentially bent panels. Damage is also visible on the concrete terraces and parapets.

Inspection

We identified the defects through a random inspection of the façade: both of what is visible from the public space and from the terraces of a significant number of flats. The visual inspection was complemented by a review of the available plan and detail material so that implementation details could be determined.

Analysis

A literature review into the cause of the saucerised natural stone panels provided a risk analysis into possible subsequent damage. The options for thorough cleaning of the natural stone, and the effect this could have on saucer and non- saucer panels, were also investigated.

Besides the natural stone, attention was also paid to the concrete elements such as the parapet for the terraces, the on-site poured terrace floors and, to a lesser extent, the elastic joints between the natural stone elements. The damage patterns were mapped and analysed.

Renovation scenarios

Based on the analysis, different scenarios were worked out for a facade renovation of the building.

Finally, the technical principles of a preservation option were indicated, as were those for an energetic renovation of the various envelope components, with a view to avoiding thermal bridges.

For each of these options, principle details were outlined, a plan of action was provided for further elaboration, and a first rough estimate of the cost price for these works was provided.

A building audit is often a crucial sub-study within a feasibility study and sometimes for a maintenance recommendation.

From façade audit to renovation

The façade audit served as the starting point for a wider renovation programme. Following the feasibility study by Bureau Bouwtechniek, a renovation master plan was drawn up in 2023. However, the damage identified to the natural stone cladding and the concrete terraces required further investigation to determine the causes, risks and most appropriate renovation strategy more accurately.

Bureau Bouwtechniek therefore coordinated further destructive testing in collaboration with Buildwise, Sanacon and the contractor BRS. Seven façade panels were dismantled to enable a materials analysis to be carried out. This also revealed the underlying façade structure: the existing mineral wool was found to be present only in limited quantities and in poor condition.

Research as a basis for targeted decisions

Buildwise investigated the material properties and mechanical strength of the existing Carrara marble panels. The investigation confirmed that the localised warping is linked to the material properties of the marble used. Furthermore, further assessment by Bureau Bouwtechniek revealed that the strength at the dowel fixings is insufficient in relation to the calculated maximum wind load. The current condition therefore poses a safety risk.

The damage to the concrete terraces was also investigated further. This revealed a combination of several factors: defects in the waterproofing, carbonation of the concrete and, in some places, the presence of chlorides. Sustainable concrete repair therefore requires, as a first step, the renewal of the terraces’ waterproofing.

Towards a comprehensive renovation

The follow-up investigation makes it possible to weigh up temporary maintenance measures against a comprehensive renovation. Merely carrying out localised repairs proves technically complex: the existing natural stone is brittle, new and existing marble panels differ in appearance, and the number of panels requiring intervention is greater than initially anticipated. Consequently, the difference compared with a full energy-efficiency renovation is narrowing, both in terms of cost and disruption.

Bureau Bouwtechniek therefore recommends, provided the Owners’ Association has the necessary funds, opting for a comprehensive façade renovation. This will involve installing additional insulation and dismantling the marble panels, reusing them where possible and replacing or securing them further where necessary. For the terraces, a comprehensive renewal of the waterproofing will be combined with the repair of the damaged concrete areas.

Meet our specialist

From Team Renovation, Restoration & Maintenance (1)

ir. arch. Arno Van Hulle

Project architect
Maintenance consultant

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Façade inspection Hertogenpark