The conclusion was that wood is three to five times more resistant to fire than concrete or bricks. A thick wooden block does not burn, but only becomes charred on the surface. Wood’s fantastic static properties are also retained much longer at extremely high temperatures in comparison with reinforced concrete structures, for example.
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These related to the fire safety of the solid wood components, the air-tightness and safety of condensate formation within the outer wall structure, and the façade cladding.
A fire safety concept was set out for the “WOODCUBE” in conjunction with the Technical University of Darmstadt. Exemptions were granted on the design of the building components in the areas of burn rates, fire protection, and flue gas risk analysis.
Due to the system-dependent features (dowelled cross-laminated timber elements and the outer wall structure with largely non-ventilated façades), specific checks had to be carried out as part of the planning process. The fire safety requirements for multistorey residential buildings are easily met at the “WOODCUBE”, although the relevant building regulations and technical rules do not yet stipulate this level of quality. The building was approved through individual allowances in all areas.
Fire Safety
Given that the floor height of the top (fourth) floor is approximately 12.20 m above the surface at the middle of the site, and the units in use are less than 400 m2 in size, the building meets § 2 (3) of the regulations for buildings in Class 4 (GK 4). The building’s structural properties also allow construction without thick insulating material. Nevertheless, this project has similar energy properties to those of highly insulated Passive Houses. The model energy properties demonstrated here, along with the actual energy consumption, come below the calculation values stipulated by lending institutions.
The timber used in “WOODCUBE” comes from local forests. By eliminating fire-protective encapsulation, the building components could remain visible on the inside. This meant that there was no need for additional coatings or protective structures, while the indoor climate benefits from a structure that is open to diffusion, with a higher heat storage capacity.
In order to create a healthy indoor climate without building materials that contain problematic substances, the paints are mineral, the construction panels are designed to purify the air, and the interior doors are tested for harmful substances. Integral windows with a 20 per cent lower aluminium content were installed in order to increase energy efficiency.
The “WOODCUBE” is an example of a closed material cycle in construction.
The aim is a traceable, material-specific system without hazardous waste. The unglued, solid wood boarded flooring is sealed with linseed oil, while the façade cladding is made of untreated larch wood, the insulating material of soft wood fibreboard, and all of the sealing sheets and tapes have a cellulose base. This is an important factor, as solid construction is not particularly sparing in its use of wood as a renewable resource. At present, this does not present any problems in Germany, as more wood is produced than is consumed. However, in future, and particularly in view of carbon storage and the availability of timber as a resource, the re-use of building elements for ends other than as fuel, as is prevalent today, will become more important.
At the end of the building’s life cycle, the resources could therefore be broken down into their different types and used again as building components or materials. This form of recycling represents another strand to the resource efficiency concept, as re-using the materials reduces resource consumption in the future.
The majority of the energy required for processing timber comes from renewable primary energy (the sun).
During the implementation of the project, great emphasis was placed on maximum recycling potential. Avoiding bonding and sandwich building elements meant that all levels could be divided up again. The “WOODCUBE’s” concept is optimised with a view to saving non-renewable resources and ensuring that the building can be recycled at the end of its life span.
All of the building components were made of solid wood if this was technically possible. The “WOODCUBE” is the first five-storey residential building that does not use glue or fire- protective encapsulation. In addition, the building is carbon neutral: no insulating materials that require lots of energy to manufacture were used unless absolutely necessary. All of the building materials can also be disposed of singly or reused.
Resource Efficiency and Sustainability
This urban timber building, which is free of toxins within the living area, can contribute to environmentally friendly and healthy living. In addition, there is scientific evidence that solid wood has a beneficial effect on the inhabitants. The project is aimed not only at ensuring that the building can be run in an energy-efficient way, but also at considering the use of energy in producing the materials, the impact on the health of those who use the building, and the legacy of deconstruction.
The “WOODCUBE” is made entirely of wood, with the exception of the foundations and access core. The structure, walls, insulating, materials and surfaces are all timber: wood is a smart material, and the “WOODCUBE” has harnessed its positive properties.
The central access core was built in class 3 reinforced concrete throughout, as were the walls and stair landings. The flights of stairs were assembled as precast concrete components.
Sustainability was the key idea behind the “WOODCUBE” project. This informed the decision to use chemically untreated, carbon-neutral wood as a construction material. In addition, the upper sides of the floor and ceiling elements have dual-layered dry screed on 60 mm mineral fill and 30 mm mineral fibre insulation in order to ensure noise protection. On top of this is the floor structure itself, made of solid timber boards on battens. Another soft wood fibreboard lies between the battens.
In addition, these supports are also found at the joins with the ceiling-like joists for the outer wall structure and as supports for the solid timber window lintels around the medium-sized and large window openings. Below the lintels above the large window openings are more steel beams that act as core support.
The balcony slabs take the form of continuous ceiling elements, designed as cantilevered single-span girders.
In areas of higher loads due to the building components on top of them (in particular, underneath the cantilevered balcony slabs), solid timber supports are integrated into the outer wall structure. This means that the floor surfaces allow for flexible layouts and uses. The joists act as composite cross-sections of the combination of solid timber beams with a vertical UPE steel profile. The ceiling elements are attached to the solid wood beams by fully threaded screws, wedged into the steel profile with wooden fillers.
The ceiling elements stretch from the exterior walls to the staircase core built in concrete, to which they are connected by a floating T-square. Ceiling-like joists for the stacked board element supports are positioned in such a way as to take account of the staircase walls and balconies in the case of an extension.
The floor and ceiling structure consists of the following elements:
• 6 cm insulating board, including battens and solid wood floor • 2 cm dry screed elements (glued to the front end) • Kraft paper as a dividing layer • 2 cm dry screed elements (placed in the gaps) • 3 cm footfall sound insulation – Isover Akustic EP1 • 6 cm Fermacell honeycomb paper infill • Kraft paper as trickle protection • 23.5 cm Holz100 ceiling Floor and Ceiling Elements and Access
The roof structure and the floor and ceiling elements also consist of unglued cross-laminated board elements, to the top and underside of which boards are applied at right angles. These 2.5 cm thick board layers are fastened to the board stack elements with beech wood dowels. |
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