According to managing director Andreas Reßle, the idea behind the event was to present the entire range of business activities of both companies to existing and potential partners in architecture, planning, and construction sectors. The companies’ activities cover the entire timber value chain: from the in-house sawmill and their proprietary mass timber construction system to the planning and assembly of the buildings.
H.R.W. Vollholzwandsystem handles the planning and execution of the timber construction work, while ARS Starkholzplatten is responsible for production. Both companies employ over 100 people. More than 1,000 projects have already been completed with the H.R.W. system, primarily in the DACH region, but occasionally also beyond. According to Reßle, mass timber elements have been shipped as far as to Canada. H.R.W. assembles around half of the buildings, while the remainder is handled by partner companies. “We can easily manage projects in building classes 4 and 5,” Reßle emphasizes. In 2021, he established a separate company for large-scale projects. In addition to new buildings, renovation projects can also be found in the order books. “Research and development are very important to us, for example, when it comes to the use of hardwood in response to changing raw material availability,” Reßle explains. Another important topic is the possibility to disassemble buildings.
From log to construction element
The master carpenter laid the foundation for this in 2009, with the development of a three-layer wall system. Contrary to CLT, the H.R.W. system’s middle layers consist of vertically positioned lamellas that are not glued together. “The middle layer is stabilized solely by the top layers. “This reduces the amount of adhesive required, and we can perforate them to improve the lambda value,” Rainer König, Head of Research and Development at H.R.W., explains. Depending on the dimensions, the panels with a perforated middle layer achieve thermal conductivity values of 0.072 W/mK or 0.095W/mK if the middle layer is made of solid wood. “These lambda values, which are unusual for the timber construction industry, result from the very dry wood used in production. The moisture content is around 7%,” König adds. Therefore, with a wall thickness of 300 mm, no additional insulation is required for buildings. Therefore, no additional insulation is required for walls with a thickness of 300 mm, according to the German Building Energy Act.
In 2018, Reßle acquired a disused sawmill and completely modernized it. An estimated 35,000 to 40,000 m³ of log wood a year are cut at the sawmill. The company places great importance on purchasing regionally sourced log wood: In fact, the log wood used grows, on average, within a 20-km radius. ARS works with two gangsaws. First, logs with a maximum diameter of 75 cm are pre-cut before being rip-cut into squared timber on a resaw. According to ARS, the yield is between 75 and 85%. For diameters of up to 1.2 m, a band saw is available. As Reßle reveals, the company has already used tried cutting hardwood logs with that saw. The lumber is dried to a moisture content of 6 to 8% in three drying kilns, with a total capacity of around 1,000 m³. When drying the lumber, the company takes care to raise the core temperature sufficiently in order to reliably destroy the protein that serves as food to wood-boring insects.
Element production starts with the visual sorting and grading of the wood, followed by finger jointing, cross-cutting, and planing. Suitable lamellas can be planed and cross-cut immediately after sorting. Bundled in layers, the lamellas are then used for panel production. Another quality check is done during assembly. “We have high standards when it comes to surface quality. Therefore, we grind each element on both sides after pressing,” ARS plant manager Christian Schamper tells us. The press is designed for maximum formats of 15.5 by 3.45 m. A 2.6-MW heating plant that is powered with wood waste from the sawmill and production provides the heat for drying and hot pressing.
Further developed machine components
Two joinery machines are available for further processing: a five-axis Hundegger PBA-D and, for the past three years, a five-axis SCM Area XL. The latter was the first machine with this particular configuration worldwide to be installed. “Since an ever-higher degree of prefabrication is required, the elements sometimes arrive on the construction site with claddings and other wood-based materials attached. In these cases, though, the vacuum lifting devices of the overhead cranes don’t work. For the gentle handling of the finished panels, we had a solution developed that uses hydraulic grabs,” Schamper explains, highlighting another special feature in the joinery hall.
News from research and development
In addition to the presenting the company to participants and exchanging sharing expertise, several lectures were also given at the Timber Construction Day. H.R.W. application engineer Matthäus Haseitl explained the smooth process from handing over the plans to creating machine data for joining. Maria Herzog and König presented excerpts from the H.R.W.’s catalog of building components. A key innovation is the latest fire safety certification for the thick wooden panels, developed in collaboration with engineering firm Fire & Timber. The determined charring rates are to be integrated into standard structural analysis software in the future.
Concluding the lectures, Dr. Michael Merk, from the Chair of Timber Structures and Building Construction at the Technical University of Munich and managing director of Fire & Timber, answered questions about the new Model Timber Construction Guideline.
