From the log to the finished mass timber element

Actually, Andreas Reßle is a passionate master carpenter. While he was still in master school in 2009, he developed and built the ARS thick wood panel, a solid wood element which can be used for walls, roofs and ceilings. Contrary to other systems, however, the ARS thick wood panels’ middle layers consist of vertically positioned lamellas which are not glued together. The top layers with a thickness of 9 to 46 mm provide the necessary structural stability.

Over the years, Reßle has optimized his thick wood panels, which are now available with grooved lamellas in the middle layer, for example. These ensure improved insulation performance. But more on that later.

Back to the roots

In 2017, Reßle had the opportunity to buy the then shuttered sawmill at the ARS production site in Roßhaupten. “At first, I was laughed at for taking this step. Then, the coronavirus pandemic came, and lumber prices skyrocketed. I think we bought the sawmill at exactly the right time,” Reßle says with a smile. “Being largely independent has always been important to me. So, it was the right step.” As an absolute newcomer in the sawmill industry, only a few thousand cubic meters could be cut in the first year. Now, production is being ramped up, and the cutting capacity currently totals 40,000 m³ a year with one gangsaw each for pre- and post-cutting.

With the sawmill, the company now has control over production, yield, quality and origin. From the region for the region: This motto is now even more true at ARS. “We often buy logs from forests that are just a few kilometers away. Our average purchasing radius is 20 km,” Rainer König, responsible for technology as well as research & development at ARS Starkholzplatten, explains during a tour of the factory. In addition, the company can process virtually all diameters: In addition to the gangsaw, a log band saw is also available for cutting. It goes without saying that the produced lumber is also dried in Roßhaupten. This is because of another special feature of the mass timber elements which are produced later on: “We need a wood moisture content of 6 to 8% in order to be able to offer visible wooden surfaces without cracks or shrinkage,” König explains, and Reßle adds: “During the drying process, we make sure that the heat reaches the core of the wood in order to make it resistant to pests.” In 2020, the burnt-down plant for the middle layers was rebuilt as a joinery hall including modern CNC and lifting technology. Last year, the company invested in a 4 MW heating plant.

“In Roßhaupten, we can map the entire production process, including the utilization of waste materials. With our associated company HRW Vollholzwand in Peiting, which is just a few kilometers away, we also offer planning and consulting services to our partners and customers – increasingly for multi-story buildings and residential construction as well,” Reßle tells us and adds: “We work on an equal footing with carpenters, planners and customers and offer them the entire range of standard thick wood panels via ARS Starkholzplatten.” HRW employs a further 50 people, including the carpentry department.

Products for every area of application

ARS manufactures thick wood panels with dimensions of up to 3.45 by 15.5 m. Thicknesses and designs vary depending on the area of application. What mainly distinguishes ARS’s panels from other mass timber elements is their above-mentioned structure. The middle layer consists of vertically positioned lamellas which are not glued together. Instead, they are connected by the outer top layers. “This way, we need significantly smaller quantities of adhesive,” König tells us. This is where the wood moisture content comes into play, since melamine adhesive is used for the ARS thick wood panels. “When using a PU adhesive, you need a higher wood moisture content. We can press elements with an average moisture content of 7% using a hot process. Also, the lower wood moisture content enables us to achieve better insulation values,” König explains. For insulation values of well below 0.1 W/(mK), the grooves described above are milled into the middle layer in some products.

Usually, the middle layers are always made of spruce wood, whereas spruce, fir or Douglas fir are used for the top layers. The thick wood panels are usually made of three layers and are available in different surface qualities. If visible ceilings are required, an 8.5 mm thick lamella with narrow sides glued is added on top. During the tour of the factory, König points out the particularly wide and cleanly finger-jointed lamellas with tiny fingers.

Efficient use of resources

Reßle and König are particularly concerned with the efficient and targeted use of resources. For this reason, they are doing research on new products. “We are keeping the current changes made to the composition of forests in mind and are reacting to it. That is why we are currently developing and producing thick wood panels with various hardwoods for the top layers,” König says, pointing to some sample products during the tour.

In this respect, one challenge is the finger jointing of local beech, ash and other hardwood lumber. However, the products still have to obtain the appropriate certifications and approvals before they can be used on construction sites.