Attractive roof executed with precision

The wooden ceiling was structured by slim ribs and an above average web height. The Knippers Helbig engineers worked out the structural design together with the Auer Weber’s architects. The design was implemented in collaboration with the wood construction company Holzbau Amann from Bannholz, Germany, which was in charge of the implementation. Use of Metsä Wood’s Kerto® LVL Q-panels made the desired roof appearance and the structure possible.

The dimensions of the roof are impressive. The structure was produced using the Kerto LVL web with a height of 1,1 metres and a thickness of only 75 millimetres. With this slim design, the structure spans an unbelievable range of 23.75 metres. There is also an unusual use of bearing surfaces and the web in the bearing area has a very low carrying height. This was possible only because of the specific material properties of Kerto LVL, the unparalleled laminated veneer lumber product.

23,75 metres long wooden roof elements

A range of over 23 metres could be achieved using a variety of structures and wood materials. But the challenge was in the engineering design of the roof structure. “Slim ribs only 75 millimetres thick which had to be made with a height of 1,100 millimetres were attached to form a π element with roof panels made of 69 mm Kerto LVL Q-panel,” explains Hendrik Pfeffinger, the project manager at Holzbau Amann, and continues that, “in addition, we went beyond standards, such as the ratio of thickness to the height of the beams, so special solutions had to be established which would on the one hand meet the requirements of Knippers Helbig, while at the same time conforming to the structural analyses and approvals in Luxembourg.”

Stability with LVL panels

The goal of the structural design was to create a wooden rib ceiling with deep cassettes which would match the large spatial volume. The dimensional stability of the Kerto LVL web was a great advantage here. As a result, the engineers were able to develop the roof surface with precise torsion-resistant webs. To achieve stability from the outset and take advantage of a high degree of prefabrication, Amann joined the Q-panel webs in pairs or even three at a time to the elements.

The extremely long wooden roof elements were prefabricated at Holzbau Amann’s factory and delivered by extra-long trucks to the construction site. Although the elements are 23.75 metres in length, their installation was quick and required only two carpenters on site. The end faces were finished off with end panels, to finalise the appearance of the roof. Quite noteworthy are the bearing notches, which are very large when compared to the size of the elements (structural components). They are on concrete ring beams on one side and on precisely positioned steel beams on the other. This required the highest degree of precision from all those involved in the construction.