Renovating a castle

The history of Castle Ravenhof.

The site of the current Ravenhof has a rich history dating back to the 13th and 14th centuries. The castle, surrounded by a park and forests, on the border between Belgium and the Netherlands, was built during the 19th and early 20th centuries in neo-Louis XV style by the Moretus family. In the early 20th century, this noble family also built the coach house. The property then came into the possession of the Assumptionist Fathers, who in the mid-20th century erected two modernist buildings on either side of the forecourt.

In 1979, the castle, along with the three outbuildings and 25 hectares of surrounding parkland on Belgian territory, was sold to the municipality of Stabroek. The castle was used for various associations in Stabroek for a long time, but a new vision for the future and, above all, a thorough restoration of the castle became necessary.

Project coordinator at the Kempisch Landschap Foundation, Johan Van den Mooter, explains: "The municipality of Stabroek wishes to restore the castle in various phases. The first phase involves the restoration of the exterior joinery, glass panels, fittings, and wrought ironwork for the windows and gates of the castle. This must coincide with an energy optimization of the building, as this is necessary for the future use of the castle as a seminar and catering space, as well as premises for community activities."

The restoration project: first phase restoration of joinery and glass.

The restoration of the joinery and replacement of the glass are the first steps in realizing the future plan for the protected castle.

In terms of glass applications, Castle Ravenhof is a showcase for the glass industry and craftsmanship from the early 20th century. For an architectural firm, Castle Ravenhof is a fine reference for improving energy performance with exceptional joinery assemblies.

Karuur Architects have been appointed as architects for this initial restoration phase. With a specialization in the restoration of monumental buildings, they are an excellent choice. Their task involved material-technical investigations and the preparation of a restoration proposal for the joinery, glazing, window fittings, wrought iron window bars, and glazed wrought iron gates. In order to examine how the energy performance of the building could be improved, an energy audit for heritage buildings was also carried out. All of this required a detailed analysis of the components, including all windows of the castle. The windows contain original drawn glass from the early 20th century, some of which is curved (convex). Later additions were made with modern float glass, but the restoration concept involves bringing together the preserved original drawn glazing in certain areas of the castle; for the remaining parts, the integration of thinner double glazing was an option.?

The goal is to preserve the oak joinery as much as possible and locally restore it where necessary.

Improving the energy performance of historical joinery without distorting its appearance is meticulous work. Only through close collaboration between architect, contractor, and glass supplier can the design be realized in practice.

The contractor - Verstraete Vanhecke joinery.

With years of experience as a general contractor, Verstraete Vanhecke is a unique and reliable partner for such complex restoration works. For five generations, they have combined experience and expertise in all aspects of the construction process, acquired through the construction and restoration of schools, churches, and monasteries, among others.

The Verstraete Vanhecke team specializes in contemporary exclusive and sustainably custom-made interior and exterior joinery. Additionally, they possess all the techniques for the restoration and adaptation of historical joinery.

Our role as glass manufacturer

"The original protected joinery with glass remains intact, but to reduce energy losses, new glass is provided in certain places. This 'thinned double glazing' consists of 2 layers of 3 mm glass with a gas-filled gap of 6 mm. To install the new glass in the existing window, a small edge of wood is milled away from the old joinery. This requires craftsmanship and precision," explains Michel Quetin, restoration glass specialist at Sprimoglass.

Over the years, the castle has undergone various renovations, with modern float glass replacing the old drawn glass. This smooth glass reflects light. However, for the restoration, the architects specify glass with the characteristics of Fourcault glass. This glass, patented in 1901 and developed by Belgian engineer émile Fourcault, was produced in a unique way by vertically pulling the molten glass mass and subjecting it to a controlled cooling process.

The glass is known for its visible streaks in the pulling direction. This technique disappeared with the introduction of float glass from 1950 onwards. We have developed an industrial variant that approximates the appearance of the original drawn glass. This restoration glass, known as our Vectio glass, is now used for the restoration of interwar heritage.

Michel Quetin specifies the challenges we face. "Vectio glass must be produced with exactly the same special shapes as the old glass panels of Castle Ravenhof. These are not only special arches, 'chapeaux de gendarmes,' and 'oeil de boeuf,' sometimes the glass itself must also be curved. This requires specific knowledge of the production process, especially given the limited thickness of the glass."

Verstraete Vanhecke provides digital drawings which we adapt for the production process in the factory. Moulds are used to create the special shapes. The glass is heated to 600 to 700 degrees in special ovens to take on the shape of the mould. Then the glass must cool down in a controlled manner. The production time for one large piece of glass quickly requires 8 hours, and each replacement glass part consists of two insulating panes. This means 2 working days for 1 large glass part.

Our second challenge is the large amount of glass that needs to be supplied. Approximately 100 panes of flat thinned double glazing need to be delivered, amounting to 151m2. In addition, there is 55m2 of curved thinned double glazing to be supplied and 37m2 of laminated patterned glass for the wrought iron gates.