## 9 Building Occupancy and Use
### Module Level
On the other hand, the bathroom, kitchen, and plant-room modules are installed on finished floors to transfer external loads [112]. Timber framing has been a prevalent construction method in the residential sector for modular housing since the 1960s, especially in the United States. Initially used in modular construction, particularly in temporary or relocatable buildings, this approach relies on prefabricated timber wall panels utilizing wall studs with a corresponding top and bottom track. Typically sheathed with plywood or oriented strand board (OSB), these wall panels incorporate one or two layers of plasterboard on the interior. The external walls are insulated externally with rigid insulation boards or with mineral wool placed between the timber studs. There is also a vapor barrier and a waterproof membrane. Floor and ceiling panels, designed with deeper joists, may include edge beams such as deep laminated beams, enabling up to 10 m spans between corner posts [93]. To optimize the strength and stability of the structure, it is a common practice to use varied stud spacings depending on the loads to which the modules are subjected: modules on lower floors have reduced stud spacing, while modules on upper floors, with less load, have larger stud spacings. Over time, timber modular systems have evolved into versatile solutions suitable for both temporary and permanent constructions, accommodating a variety of functions. The construction techniques employed in timber buildings encompass timber framing for low-rise timber structures and post-beam and paneling systems for high-rise mass-timber projects, both strategically organized according to modular principles [81]. However, systematically dividing timber construction into more general methods such as panel, frame, and solid timber construction no longer seems reasonable in this context. By intelligently combining various building elements, customized solutions can be created in practice, giving planners the greatest possible design freedom. One frequent combination is timber panel exterior walls and ceilings and load-bearing interior walls made of dowel laminated timber or glued laminated timber, using the elements' thermal insulation, soundproofing, and fire safety advantages. Planar structural components have always been combined to brace structures and enclose spaces in frame structures [86]. The widespread practice of combining timber with other materials, such as reinforced concrete or steel, in construction has led to the creation of timber-concrete composite (TCC) and steel-timber composite (STC) components [106]. TCC solutions are commonly applied to beams, floors, and walls at the module level. TCC beams consist of a timber beam coupled with reinforced concrete in the transversal or longitudinal direction. TCC slabs, a well-known hybrid component, feature a slab-type EWP or timber beams in a joisted system connected to a reinforced concrete slab through shear connectors. TCC walls are created by connecting a massive timber or framed structure to a reinforced concrete slab with various materials such as solid timber, GLT (glued laminated timber), LVL, adhesive-free EWPs, regular concrete, lightweight concrete, or high-performance concrete. TCC fabrication can occur in wet-dry or dry-dry construction systems, involving processes where wet concrete is poured onto dry timber or precast concrete is connected to the timber part, respectively [106]. STC solutions are frequently employed in construction, especially when there is a need to distribute heavy loads across multiple points. Steel elements are used as connectors in frame construction, integrated into box or slab elements, and inserted in prestressed beams or frame structures through steel cables. This integration allows for longer spans, flush beams and joists, and more slender support cross-sections in modern timber buildings.