In the early 2000s, two German timber construction specialists were contemplating a future where buildings will increasingly have to combine affordability, minimal carbon footprint and maximum flexibility. They sat down to work out how engineered wood could rise to the challenge.
Kielsteg, the hollow-core panel solution Stefan Krestel and Ulrich Spiegel devised, scores on all three criteria.
In fact, this lightweight composite of solid timber and sheet materials exceeded expectations and has now been used in hundreds of buildings Europe-wide, from private homes to warehouses. It also won this year’s TTJ Awards’ Achievement in Engineered Timber.
TTJ was told the Kielsteg story by Dieter Penninck, director of Belgian-based glulam and CLT manufacturing and construction specialist Korlam, now Kielsteg’s exclusive market partner for Western Europe, and soon to be a producer too.
He’s clearly an enthusiast for the product and sees the UK as a prime potential market.
“Kielsteg panels’ combination of strength and lightness creates structural options for wood that did not exist before,” he said.
“They can be used economically at clear spans of 5-6m upwards, which is where existing solid wood elements start to be less cost effective.
So they’re not intended as competition for products like glulam and CLT, they enlarge the timber construction market.”
The original product development motto of Krestel and Spiegel was “less material, lower cost” and, while it’s clearly been fine-tuned since, they came up with a concept that achieved their aim from the outset.
Kielsteg means “keel-web” and the name derives from the S-shaped sheet materials flanges that form the core of its sandwich structure.
The panels comprise two layers of finger-jointed C24 43-57mm thick (depending on specification) spruce lumber chords arranged lengthways. Between these, the curving flanges are glued to form an extremely strong cellular structure.
In the 228mm to 380mm panel thicknesses, they comprise 3-ply 4mm spruce and pine plywood, and in the 485mm to 800mm products, 10mm and 12mm OSB3.
For ease of production and handling, all panels are 1.2m wide, with individual lengths up to 35m.
They are fixed by screwing each end to the substructure, with joint boards used on the upper invisible side to tie each panel to the next. On the visible underside the profiles of the outer chords interlock.
The target was initially for the product to span widths to a maximum 10-15m. But prototyping and tests undertaken at Graz Technical University showed Kielsteg could cope with free single-beam spans up to 27m and continuous beam structures up to 35m.
Kielsteg is made in flat and cambered formats and designed to form floors, ceilings and roofs in all types of construction, from individual private housing, to schools. But it is clearly particularly suited to large-scale industrial/commercial building.
“The large clear spans achievable meet the increasing demand on architects to create interior spaces that can be rearranged through the lifetime of the structure, depending on the changing needs of occupants,” said Mr Penninck.
“Manufacturing businesses these days must be able to react, reorganise and adapt their facilities to markets that are following shorter and shorter demand cycles.”
Kielsteg included an example of the sort of space that can be achieved in its TTJ Awards’ Achievement in Engineered Timber Award entry. This was the new factory of leading German interiors business Baieri & Demmelhuber.
The 3000m2 open-plan plant features cambered 73cmx21.5m Kielsteg panels, each weighing three tonnes and supported by the walls and just three columns mid-line, creating a vast open plan factory floor.
The fact that Kielsteg can be used for cantilevered projections up to 10m also suits it to big industrial premises.
From the beginning Kielsteg was also designed to be a mass-manufactured product, and to this end, following initial development and prototyping, the creators started working with Kulmer, an Austrian construction company and manufacturer of building products, including glulam.
They, in turn collaborated with mechanical engineering specialists Minda to devise a highly efficient, automated production system.
“Kulmer is now a strategic partner of Kielsteg and exclusive producer in Austria and expanded its 11,000m2 laminated timber manufacture and timber framework plant for the product,” said Mr Penninck.
The production line includes finger-jointing, planning, jointing and pressing operations in one continual process and has annual capacity of 44,000m2, using just two operators.
“Production is also monitored externally by Stuttgart University’s materials testing institute,” said Mr Penninck.
Given the increasing environmental sensitivities of modern European construction, and the ever tougher emission, energy and waste controls it faces, another key sales hook for Kielsteg is clearly the fact that it makes more wood go further.
On this basis, it was also shortlisted for the TTJ Environmental Achievement Award. “The goal was to find the optimum of maximising use of timber across the market to bind in as much CO2 as possible, and at the same time make more efficient use of the resource,” said Mr Penninck.
“Kielsteg achieves this by putting the wood elements where they contribute most to static performance. The result is a product that weighs an average 50kg/m2, so can be handled and transported easily, and achieves a materials saving over equivalent solid timber components of 50%.”
The Kielsteg package includes prefabrication of the panels to specification, and erection if required, although it maintains that any company with experience in CLT and other solid timber building could use it. It provides a full technical workbook and continuous professional development presentations for architects, contractors and engineers are available.
Kielsteg is backed by German Product Approval and first draft of its application for European Technical Assessment (ETA) is in process. The next step will be to increase output further and extend the product’s market reach and Korlam is clearly central to growth plans.
“Our engineering team is already servicing Kielsteg projects and it is the stated intent of our partnership to manufacture the product in the north of Belgium, with timing dependent on market development,” said Mr Penninck.
“This will enable us to offer shorter lead times, lower transport costs and generally better service to local markets where there is a growing use of engineered timber, including the UK.”
