In order to fulfill the requirements for the structural engineering of five-storey residential buildings, solid wood supports were integrated into the load-bearing outer walls, in contrast to the existing regulations.
Such efforts are also being made with regard to the KfW, in order to ensure that stronger support frameworks will be provided on a holistic basis over the whole life cycle of the building, in particular with regard to embodied (grey) energy and the carbon balance.
Overall, the Wohnungsbaukreditanstalt (building society) deemed the project to pass the "hot box test process“ and established the dynamic U-value. This is an important step towards ensuring that comparable timber structures will be available for everyone.
In addition, the system was optimised on the basis of comprehensive studies in order to ensure that the building would comply with ongoing regulations for classifying buildings according to the KfW-40 standard. In order to meet the higher requirements envisaged for the “WOODCUBE”, an additional 4 cm thick soft wood insulation fibreboard was incorporated into the construction.
They differ from standard elements by containing an inlaid soft wood fibreboard (providing insulation), and milled grooves in the individual board layers (integrated structural insulation). They provide macroscopic air cushions without circulation within the wall and reduce the wall’s thermal conductivity, thus considerably improving the thermal insulation effect.
There is no other gluing, bonding or nails, resulting in a solid timber wall (up to 3 × 8 m in size, with a thickness of up to 40 cm), containing only wood.
The DeepGreen/Holz100 walls used during the construction process were developed specifically for the “WOODCUBE”. Like the standard Thoma Holz100 timber walls, these consist of board layers 20-80 mm thick.
In the factory the exterior walls are fitted with a layer of wind paper, positioned between two board layers. The mechanically compressed and bone-dry hardwood dowels are hydraulically injected, and thus dampened, and take in additional moisture from their surroundings, swelling up inseparably within the wood around them.
All of the joins within the DeepGreen/Holz100 elements are glueless and purely mechanical. The connections are all non-toxic and meet the requirements for increased noise protection and smoke control.
The elements developed by DeepGreen consist of board layers ranging from 20 mm to 60 mm thick, laid crosswise (horizontally, vertically, and diagonally) on the inside and outside, with a vertical core, and top and bottom cords of 40 and 80 mm connected using beech wood dowels (approx. 20 mm thick) placed in the middle of the grid.
The exterior wood panelling is 26 mm thick, slotted, ventilated board cladding made of untreated larch wood. The formation of the lathing is innovative, with closed 60 cm × 60 cm coffers that act as “small fire compartments”. The interior walls, including the dividing walls within the apartments, are dry, mortarless constructions that are not load-bearing or stiffening.
The timber used is 95 per cent fir wood and 5 per cent spruce, while the load-bearing solid timber core is grading class S 10 (strength class C 24), in accordance with DIN 4074-1. The average bulk density of the Holz100 element, as a solid timber composite cross-section, is 435 kg/m3. The composite dowels consist of predried beech wood.
The results in a 32 cm thick solid timber element dowelled in crosswise and diagonal layers. The solid wood element consists of an 80 mm thick static core layer and room-side board layers ranging in thickness from 29 mm to 26 mm, applied crosswise and diagonally as fire protective sacrificial layers.
From the inside to the outside, the exterior wall elements have a total thickness of 32.4 cm (heat transfer coefficient = 0.19 W/m2*K), as follows:
• 25.1 cm dowelled cross-laminated fir wood elements
• 4.4 cm soft wood fibreboard
• 2.9 cm fir wood board layer
The beech wood dowels are kiln-dried and incorporated during the manufacture of the elements, and swell up to the building humidity (approx. 15% ± 3%), so that they adjust to the pressure on the soffits of the holes. No separate component to ensure airtightness is necessary.
(the spacing scheme is 30 cm lengthways and 24 cm at right angles, whereby the rows of dowels are offset in a lengthways direction, 15 cm from one another). The mechanical join within the board stack elements works using friction between the beech wood dowels and the perforations in the cross-laminated timber elements.
The outer walls are made of solid timber with cross-laminated timber elements. The board layers of these elements were fixed and mechanically joined to beech wood dowels using a specific system (DeepGreen/Holz100). The dowels are placed at right angles to the board layers, at frequent intervals
High quality materials such as solid timber boards can also be re-integrated during conversion work. Empty ducts and flexible connection options (Homeway) also ensure maximum flexibility for building services in case of renovation or conversion.
Due to the permeable structure with highly insulating building components, these problems are virtually eliminated. The façade construction was examined in a durability simulation so as to ensure that living costs remain as low as possible. Optimal construction, fire safety, humidity control, and a weather-proof structure go hand-in-hand.
Holz100 Canada Inc.