Innovative window sill for changing construction

After more than half a century, the time has come: an entirely new type of window sill is entering the market. It is a pioneering product, because it is not made of stone or metal, but of glass. IsoSill' window sill (registered trademark) provides an answer to the long-standing problem of thermal bridges under windows in otherwise well-insulated facades. And there are more and more of them, as construction is changing under the influence of climate change. Bart Tenbült, director and owner of Raamdorpelelementen BV in Bladel, thinks it's high time his company responded with a suitable and cleverly conceived product.

Window sills have actually been around as long as there have been window frames. They are mostly made of heavy materials: ceramic, natural stone and concrete. Then came aluminum and finally - over half a century ago - Holonite, a composite material. But that was and is it. We don't see much development in this industry when it comes to the basic product. Bart Tenbült saw his business grow and grow in the years since, but he also saw the shape and material change in the facades where his window sill elements come in. 'Insulation' is the key word that raised the question in his mind whether there was no better solution to the almost inevitable thermal bridge in those well-insulated facades. After two years of struggling with the existing window sills, he took a different approach: back to the drawing board, so to speak, in other words: inventing a new type of window sill with optimal insulation and a thermal bridge-free connection from scratch.

Quest for solutions

It is from this own custom production that the penny dropped for Bart Tenbült. A matter of out-of-the-box thinking. Bart said it before: "Construction is changing. Better and better insulated facades are coming on the market, with much thicker layers of insulation, a finish of stucco or stone strips, and we see an increasing combination with timber construction. It means that a heavy window sill can no longer lean on a solid foundation like the traditional brick exterior shell. As an intermediate solution, we then opt for metal angle irons as support, but that does create a considerable thermal bridge and that is at odds with the desired optimal insulation value of the facade."

It became the starting point of a years-long search. The innovative product had to be reasonably easy to make, customized of course, and furthermore lightweight and manufactured in-house. And, of course, the innovation had to meet the most important requirement: optimal insulation. That in the first place determined the choice of EPS as the core.

IsoSill: The insulating window sill

EPS is light, load-bearing, easy to form and it has a very high insulation value, exactly the properties Bart was looking for for the new window sill. By then using GRP (fiberglass-reinforced plastic) as the casing, the innovative IsoSill window sill was born.

The EPS core is encased by a 3 mm thick layer of fiberglass. That sheathing is insulating, strong and lightweight as well as impact resistant and easy to customize. According to Bart, these window sills are super strong and easy to repair if necessary. The maximum deliverable length from one piece is 3 meters, and there will eventually be several depth variants in addition to the current standard depth of 160 mm. The fiberglass headers are glued to them on the face side, after which the custom-made window sills are finished with a two-component paint that is sprayed - in color - onto them.

Weighing 3 kg per meter, the innovative window sills are many times lighter than those made of ceramic, natural stone and concrete, which has its own advantages. More durable to transport and can be laid on site in long lengths without tools. In addition to the window sill, there is also an IsoSill sash, so that the architect does not have to hold back in this regard.