The attitudes of residents towards new construction methods (e.g., a wooden additional floor) have an important role in the spread of these practices
[59]. Moreover, the positive attitude of residents is a critical aspect in the effective execution of extensive refurbishment
[60]. In this sense, the survey by Karjalainen et al.
[25] showed that participants generally assessed the construction of wooden additional floors positively and thought that it would contribute to the attractiveness of the residential area.
The combustibility of timber may limit its use as a construction material in Finland, as in many countries, due to constraints on building regulations
[61][62][63]. Various studies have been carried out recently on the fire behavior of wooden buildings around the world, aiming to provide fundamental data on the safe use of wood (e.g.,
[64]). As a result of extensive testing, new fire design concepts and models were developed, and existing advanced knowledge in the fire design area of wooden structures together with technical precautions, especially well-equipped fire services and sprinkler systems, ensure the safe use of wood in a wide range of applications as seen in the building code relaxations introduced in recent years
[65]. In this sense, fire safety engineering and performance-based design offer benefits and challenges for the use of timber in buildings, where the performance-based approach is primarily based on the use of fire engineering principles, calculations, and modeling instruments (e.g., structural models, thermal models) to meet building regulations, considering fire modeling, full-scale structural fire experiments, and experience from fire accidents in timber structures
[66][67][68][69]. Additionally, the following considerations stand out in terms of the implementation of fire safety design in wooden structures
[70][71][72][73]: Manual firefighting, sprinklers, encapsulation, fire retardants, fire performance and fall-off times of protective systems, the fire performance of connections between structural timber elements, details to prevent the internal spread of fire, external fire spread in the same building, and quality assurance. Furthermore, timber and steel structures have some similarities and differences in terms of fire safety measures
[65][74]. Some fire regulations, such as those in Canada, encourage full encapsulation of timber frames to ensure equivalent fire safety to the non-combustible steel frame structure. In terms of performance-based design, performance-based formulations of requirements for timber structures can be considered to provide a fire-safety equivalent to regulatory steel structures. Regarding structural modeling, wooden structures are usually easier to model than steel structures because the wood has poor thermal conductivity and does not undergo considerable thermal expansion. In the manual fire extinguishing strategy, the fire risk will be greatly reduced if immediate action is taken to contain the fire, and this reduction in fire load is adjusted for steel frames. This method is also permissible for timber structures. Moreover, in terms of external fire spread in the same building, timber facades can also be used as fire-resistant facade cladding in steel structures.
Issues with wooden structures, especially sound insulation and moisture, require special insulation and protection techniques. To obtain good air-borne sound insulation, the partitioning wall and intermediate floor structures should be built in layers and the layers should be separated from each other so that the sound does not pass through the structure
[75][76]. On the other hand, humidity issues lead to both reduced durability and mold growth, which can affect indoor air quality and have adverse health consequences
[77]. The best strategy for providing a moisture-resistant structure is to ensure that the wood is not exposed to water or high relative humidity for extended periods. Neglecting moisture safety can mean a high risk of damage, with extensive costs and consequent time delays for research, decontamination, or material replacement
[78].
Wood-based composite materials and wood frame-based hybrid structures are among the important topics in today’s wood construction literature. In general, owing to the destruction of forest resources and recently developed technologies for wood-based composite materials in particular, engineered wood products have gradually replaced traditional materials for residential construction
[79]. These materials are produced from similar materials based on wood products, e.g., timber or lumber processed into boards, or wood chips
[80], and the residential and commercial building construction industry is among the areas where wood-based composites are most in-demand
[81][82]. On the other hand, the idea of hybrid structures that combine multiple materials, such as timber, along with steel and/or concrete, is gaining increasing acceptance in the engineering community
[83]. Moreover, hybridizing timber with other structural materials is one of the most popular approaches for designing high-rise timber buildings
[84][85][86][87] as in the case of Brock Commons Tallwood House (Vancouver, BC, Canada, 2017)
[88].
The three critical components of timber frame construction are the floor, the roof, and the load-bearing wall, which have significant effects on occupants’ comfort. The wood floor, the most common system component, is in frequent physical contact with building inhabitants
[89]. The dynamic movement of people or objects caused by defects or deficiencies in the structural performance of the floor can cause occupant discomfort. Movements, e.g., walking, running, jumping, can create structural vibrations on the wooden floor, which adversely affect the efficiency of work and quality of life
[90]. However, environmental excitation and impact excitation vibration tests as well as comfort analyses of timber floors offer solutions to these undesirable situations
[91]. In addition, particularly nowadays, when standard structures are supported by contemporary technologies such as wooden floors combined with underfloor heating, it is necessary to meet technical guidelines and specifications during the operation of the floor as a whole
[92]. Moreover, in line with the ‘smart building’ concept, wood, namely wood flooring, is used as an ideal material to be applied in triboelectric nanogenerators for large-scale applications in smart houses
[93]. This ensures that mechanical energy (for example, the movements of residents) is directly converted into useful electricity
[94][95][96][97].
Although there are numerous research studies on different construction solutions with the use of engineered timber products with related technical features (e.g.,
[98][99][100][101][102][103][104][105][106][107][108][109]), several studies have focused on the use of wood as a building material from the viewpoint of construction professionals (e.g.,
[110][111][112][113][114][115][116][117][118][119]) and consumers or users (e.g.,
[120][121][122]). On the other hand, to date, there has been a limited number of studies on wooden additional floor applications, especially in the housing construction industry.
This entry maps out, organizes, and collates scattered information on the current state of the art, as well as benefits and challenges of wooden additional floor projects with their different stages, focusing on the case of Finland, and presents it in an accessible and understandable discourse for non-technical readers. This entry also provides a methodical literature analysis on international peer-reviewed studies and research projects. By highlighting the advantages and opportunities of these sustainable practices, the entry will contribute to an increase in the awareness of wooden additional floor construction, which has many advantages and therefore help to gain more widespread use in Finland and other countries.
In this entry, timber or wood refers to engineered timber products
[123][124], e.g., cross-laminated timber ((CLT) is a wood panel product made from gluing together layers of solid-sawn lumber), laminated veneer lumber ((LVL) is produced from veneer and is designed for structural framing where high strength and rigidity are required), and glue-laminated timber (glulam) ((GL) consists of layers of dimensional lumber glued together with durable, moisture-resistant structural adhesives).
The remainder of this entry is composed as follows: First, a literature survey is provided. This was followed by a section on the benefits, challenges, and drawbacks of wooden additional floor construction. Finally, the conclusions and prospects of the research are presented.