15.03.2022 – Workshop Report: On the Status of the Project Mono-Material Solid-Timber Construction (AP15)

When we arrive at the LCRL, the workshop of the Cluster of Excellence, Oliver Bucklin is already busy: he is sawing the last dovetails for the frame of a wall element that he is building for the series of tests on air tightness, as well as subsequent tests of thermal resistance and fire resistance.

We have an appointment to learn more about the interim status of the Mono-Material Solid Timber Construction project. As a research associate at IntCDC and ICD, Oliver Bucklin is conducting associated project research on a system for multi-story residential and office buildings that will be made of solid timber. What makes it special are the slotted spruce beams, which act as a load-bearing building envelope with increased thermal insulation while requiring no additional material.

The sample piece, like the building system, consists of an inner and an outer layer of spruce beams, sawn with insulation slots and a spline groove on each side. The assembly is held together with a frame made of solid spruce beams. The slots generate closed air chambers when the individual beams are arrayed together into wall panel elements.

For the frame, the skilled carpenter pre-saws the dovetail joints using a combination of power and hand saws and then removes any protruding remnants with the chisel. These manual processes will later be integrated into automated fabrication workflows.

Drawings © Oliver Bucklin

Oliver Bucklin demonstrated automated production capabilities in 2019 with his IBA Timber Prototype House; for the small log house, he expanded the traditional timber construction method with computer-aided design and manufacturing. Because the elements were vertically layered, unlike traditional log home construction, the slots could be milled into the wood without compromising load-bearing capacity and, as dead air chambers, significantly improved the wall's insulation values. The high-precision milled joints did not require additional metal connections or adhesives, as they were simply slotted together.

Images © Thomas Müller

The finished wall element for the test stand measures approx. 112 x 110 x 10 cm. It is integrated into the wall of an airtight chamber and sealed at the edges with membrane sealing tape. A Minneapolis Blower-Door Duct Blaster mini-fan pumps air into the chamber via a pipe and creates a positive pressure of 50 pascals. Sensors on the chamber wall now measure the pressure differential over a few minutes, which is analyzed to find the airflow permeation rate that characterizes the air tightness of the wall element. Subsequently, we measure at pressure differentials of 40 – 10 Pascal.

In order to be able to check the results, a small hole with a precisely defined diameter was also made in the chamber wall. With the help of the air flow formula, an expected airflow through the hole at a given air pressure can be. The difference in the air flow rate with the hole open and closed is measured and compared to the calculated value. In this way, the researchers can verify that the measurements have a high degree of accuracy.

We now have to wait for the evaluation of the measurements. We can probably expect them together with the results of the upcoming tests on insulation value, fire properties and the behavior of the wall element during humidity swings. In addition, visits to sawmills are scheduled in the near future: Oliver wants to optimize the production of the prototype. To do this, they will have to work with experts to determine how to strike an optimal balance between the advantages of digital manufacturing and the cost-effectiveness of established production processes.

A 6-axis industrial robot, like the one used to produce the test elements, can mill with high precision, but it takes a long time to do so. Production on standard machines, such as CNC milling, would speed up the manufacturing process, but the challenge here is to integrate production into existing production lines.

The goal for the discussions with the experts is the development of a product-ready standard profile in the sawmill. The first talks will soon take place with our network partner best wood Schneider, who, by the way, also sponsored the wood for the test series. Meanwhile, the test series will run until the end of the year. Next year, we plan to start constructing a building demonstrator. By the way, we are still looking for partners for this...

Further Information

Here you can find the description of the Assocciated Project AP 15

Here you can find more about the IBA Timber Prototyp House

We thank the company best wood Schneider for the material donation!