MATER I AL S
This Guidebook assumes a 9x6 metre grid for the office buildings in the Illustrative Examples in Section 6. This grid has been chosen for material optimisation and embodied carbon reduction, making it an efficient and sustainable choice. It is worth noting in this context that the 2023 update of the British Council for Offices (BCO) Key Design Criteria, has acknowledged the benefits of using 6-7m structural grids, balancing carbon reduction with the desire for efficient, column-free spaces. This approach prioritises sustainability alongside spatial efficiency. Structural grid sizes and layouts must be planned alongside services distribution from the early stages of the project. This coordination is vital for achieving a holistic design approach in mass timber construction.
The structural design commonly used in mass timber office buildings fall into two categories: full timber and hybrid (concrete/timber or steel/timber). In full timber structures the entire superstructure including the building’s core/s are exclusively made of engineered timber; materials other than timber are used only in the substructure and in the ground floor slab. In hybrid structures large part of the superstructure is made of materials other than timber, such as steel, reinforced concrete, or a mix of both. This type of structure generally makes use of concrete or steel both for columns, beams and core/s, with the use of timber confined to floor plates (made of CLT, composite RC/CLT or RC/GLT) and separating walls. The hybridisation of timber with other materials can enhance its structural, acoustic and vibrational performance, particularly in larger structures with longer spans.
CORE DESIGN
A core is a vertical distribution space for the circulation of building users and services, containing stairs, lifts, services risers, bathrooms or WC’s. In typical post and beam type mass timber structures, the core often also fulfils a structural function, providing lateral stability to the entire structure. The location, number, size and material (CLT or LVL, concrete or steel framed) of these cores is primarily determined by a building’s use, height, occupancy and the consequent fire escape distances. Cores can be classified into two main categories: in- grid and site-adaptive. In-grid cores are aligned with the building grid and occupy one or more structural bays (central, atrium and peripheral cores). In contrast, side-adaptive cores function outside of the structural grid, enabling a regularly shaped building to adapt to the irregularities of a real-world site. This is achieved by connecting or infilling the irregular shape between regular forms. Recent research has highlighted the prevalence of central core configurations in timber office buildings: a strategy that maximises both structural robustness and space efficiency. This allows a large number of users to be accommodated along a building’s perimeter, increasing
STRUCTURAL GRIDS
Property agents, building owners and investors expect office spaces to have a good spatial efficiency and large, adaptable column free spaces that can easily be reconfigured. These expectations emphasise the importance of selecting an optimal structural grid. For mass timber buildings, it is crucial to design the most efficient span for the structural timber frame from the beginning of the project to meet these requirements effectively. Trying to force timber into structural grids originally conceived for traditional building materials such as steel and concrete can lead to material inefficiencies. The structural grid dimensions (together with building height and structural material choice) influence the number and size of every system component. Considerations such as standard product sizes, transport, site logistics, construction speed, and material efficiency should be integrated with the overall spacial design.
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TIMBER OFFICES
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