Korslimmat trä (KL-trä) för byggnadsändamål är en produkt som togs fram i Centraleuropa i mitten av 1990-talet. Syftet med förstudien är att i samverkan utforska förslag för hur en framtida resurseffektivare KL-träprodukt kan utformas. Målet är att ta fram underlag för utveckling och genera en samling kring frågan. Det finns en medvetenhet för de omvärldsfaktorer som påverkar byggandet med KL-trä. Det finns en ökad efterfrågan på trä i byggsektorn och det finns ett dynamiskt tänkesätt för att ersätta betong med KL-trä. Ökad användning av skogsråvara, global uppvärmning och minskad tillgång via begränsningar i skogsbruk väcker frågor. Vilken råvara har vi i framtiden, vilka trädslag och hur ser tillgången ut? Det resulterande materialet har analyserats utifrån de olika perspektiven som representeras av intressentgrupperna i värdekedjan för byggande med KL-trä. Rapporten avslutas med projektidéer som framkom under arbetet med förstudien.

Cross-laminated timber (CLT) for house construction is a product that was developed in Central Europe in the mid-1990s. The purpose of this study is to collaboratively explore proposals for how a more efficient CLT product can be designed for the future. The goal is to produce a basis for development and generate a consensus around the issue. There is an awareness of the environmental factors that affect design with CLT. In addition, an increased demand for wood in the building sector has resulted in a dynamic mindset to replace concrete with CLT. Increased use of forest raw materials, global warming and reduced access via restrictions in forestry raise questions such as: What raw materials will we have in the future? Which tree species will be available? How large will the supply of raw materials be? The resulting material has been analysed based on the different perspectives represented by the stakeholder groups in the value chain for building with CLT. The report concludes with project ideas that emerged during the work on the feasibility study.

The limitations in performance of band-pass filters to accurately process rapid decaying signals in lower frequency bands is an obstacle for some measurements within building acoustics. For instance, it would be beneficial to be able to accurately measure reverberation times down to the 20 Hz one-third octave band for impact sound in timber buildings. Here, it is tested whether calculations with FFT with small incremental steps may be a way to achieve discrete frequency time signals with faster performance than traditional band-pass filters. The tests show that incremental FFT gives accurate estimations of the reverberation time corresponding down to 0.1 s at 20 Hz with a spectral resolution of 2 Hz. Using the one-third octave limits it is possible to form approximate one-third octave band results. It is seen that accurate estimations of reverberation time are achievable for BT⩾0.5 (T=0.1 seconds for the 20 Hz one-third octave band) and possibly even lower, if the dynamic range in the interrupted noise signal is sufficient. The higher one-third octave results show to work as well. A disadvantage with the method is that during short reverberation times (0.1 s) there is a severe spectral leakage to the side bands. Also, the method requires higher dynamic range decay signals compared to band-pass filtered signals. If a one-third octave resolution is requested, a dynamic range of 50 dB or greater is preferable. With a coarse resolution of e.g., 10 Hz and having no averaging into one-third octave bands, it is possible to measure short reverberation times (0.1 s) with signals having close to the same dynamic range used in classical band-pass filtered reverberation time measurements. © 2022 The Author(s)

The most popular single-number quantities (SNQs) of impact sound insulation in Europe are L’n, w and L’nT, w. They are based on measurements within 100-3150 Hz. Recently, it was proposed that the measurements should be extended down to 25 Hz for wooden floors, and L’nT, w+CI, 25 should replace L’nT, w. The purpose of this study is to analyze which of the two SNQs, Ln, w or LnT, w+CI, 25, predicts the annoyance of natural impact sounds better for wooden floors. We conducted a psychoacoustic experiment, where 52 participants rated the annoyance of 75 impact sounds. As stimuli, five types of natural impact sounds were used. They were recorded for 15 different wooden floors built in an impact sound insulation laboratory, where also their SNQs were measured. Based on correlation analysis, Ln, w explained annoyance of natural impact sounds equally well or better than Ln, w+CI, 25, depending on impact sound type Therefore, based on perception, it seems to be sufficient to conduct measurements within 100-3150 Hz for wooden floors and assess their sound insulation using L’nT, w or L’n, w © 2023 First author et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Prefabricated external wall elements for CLT systems

This is a first pre-study to how building with cross-laminated timber (CLT) as a frame system in buildings could be made more efficient using prefabricated exterior wall elements as frame completion for CLT buildings. In carrying out this study, CLT building in Sweden as a rule involves an efficient frame erection of the CLT elements, but with a relatively slow phase to assemble the exterior frame completion. External frame completion of CLT buildings is usually carried out on construction scaffolding, where the layers of insulation and surface layer are built up on site. Prefabrication of the outer layers of the CLT frame that is lifted into place has the potential to save a lot of labor time and thus costs. The report presents requirements and practical aspects that must be taken into account in order for prefabricated exterior wall elements to be feasible in terms of requirements and in practice. The purpose of the report has also been to give tips, inspiration and ideas to consider when producing prefabricated exterior wall elements. In the study, an example solution has been developed with the aim of being wood based to as high degree as possible. The result shows that with relatively simple means it is possible to build a prefabricated wall element that meets established requirements. It is desirable that the outer wall elements are hung in place with the minimum possible finishing work on the facade. When it comes to the division of external wall elements, it is practical to follow a similar division and measurements as for the CLT boards to facilitate handling, assembly and lifting. It should be avoided to have sockets (window panes, door holes and the like) that are broken in its interface between the external wall elements to facilitate uniformity in the dimensioning of the elements. The study shows that it is realistic to create prefabricated exterior wall elements for CLT frames.

In a Finnish-Swedish consortium project, a large amount of sound insulation tests was conducted for several intermediate floors in laboratory conditions to serve various scientific research questions. The dataset contains 30 wooden and 8 concrete constructions which are commonly used between apartments in multistorey buildings. Impact sound insulation was determined according to ISO 10140-3 standard using both tapping machine and rubber ball as standard sound sources. Airborne sound insulation was determined according to the ISO 10140-2 standard. The data are special since they have a broad frequency range: 20−5000 Hz. Data are reported in 1/3-octave frequency bands and the single-number values of ISO 717-1 and ISO 717-2 are also reported. Detailed construction drawings are available for all reported constructions. The data are highly valuable for research, education, and development purposes since all data were obtained in the same laboratory (Turku University of Applied Sciences, Turku, Finland), and all the constructions were built by the same installation team. © 2023 The Authors

Wooden floors usually have worse impact sound insulation (ISI) at low frequencies than concrete floors having the same rating level. Rating level is usually expressed by single-number quantities (SNQs), such as weighted normalized impact sound pressure level Ln,w. Psychoacoustic research among wooden floors is very limited although a controlled laboratory experiment is the strongest method to point out the most adequate SNQs to be declared for the floors. The purpose of our study was to determine how four standardized SNQs of ISO 717-2, Ln,w, Ln,w + CI, Ln,w + CI,50, and LiA,Fmax,V,T, and a recently proposed SNQ, Ln,w + CI,25, are associated with the annoyance of natural impact sounds transmitted through wooden floors. Fifteen floors were built in the laboratory based either on cross-laminated timber (heavy) or open box wood (light) slabs. Different coverings and suspended ceilings were applied on these slabs. The ISI was tested within 25–3150 Hz using both tapping machine and rubber ball. Thereafter, five natural impact sounds were recorded for each floor: rubber ball drops, steel ball drops, walking, jumping, and chair pushing. Fifty-two people rated the annoyance of these 75 recorded natural impact sounds in psychophysics laboratory. Annoyance was best associated with Ln,w for all the five impact sound types. That is, measurement of ISI within 100–3150 Hz is sufficient from subjective point of view. All four SNQs based on tapping machine explained annoyance better than the SNQ based on rubber ball. Our results can significantly guide the future research, development, and regulations of wooden floors.

Increased construction with timber is a potential way to improve environmental impact of the construction sector. If it is done right, timber is a renewable, sustainable and requires low amount of energy in the construction phase and during its service life. Vertical extensions of buildings are a potential way to increase a buildings relevant service life and to adapt the building to the increased needs of a city. It is also a way to contribute to densify cities with less resources compared to demolish the building and to construct a new one. Vertical extensions made with timber is light, compared to for instance concrete. This decrease the need for, or amount of, reinforcements needed in the existing building that is to be extended. There is a large unused potential in vertical extensions. Only a small amount of buildings is extended during its service life. The main purpose with this guide is to support developers and people that are involved in early stages of discussions and planning vertical extension of a building. It should also be useful as a support for technical people involved vertical extensions. Interviews with consultants and construction companies have shown that projects with vertical extensions is best run slightly different compared to normal projects were one start from “an empty plot”. In a project where you start from an empty plot, the developer and architects may normally be able to work rather free and independent from designers and heating, ventilation, and air conditioning engineers, in the early part of the project. For vertical extension projects the situation is different. The existing building possess special qualities and boundary conditions. For a successful project it is important to understand these technical possibilities and limitations. This is conveniently done by educate the developer in some of these parts, in order to understand what potential different buildings may have with vertical extensions and how some selections of concepts may complicate the extension. For the architect it is also important to work closely with the structural designer and the heating, ventilation, and air conditioning engineer from the beginning of the project, as a team. Experience have shown that not doing so may give concepts that is difficult to accomplish and needs for costly revisions. The first part of the process to decide if a building is suitable for vertical extensions is to investigate the condition of the existing building. Especially the load carrying capacity of the ground and the building, possible need for reinforcement and how reinforcements may be done. This is important understandings in the earliest parts of a project that usually need to be investigated or clarified. Building vertical extensions with timber may be done with a variety of building systems. Each have its benefits and limitations. Cross Laminated Timber (CLT) and post and beam building systems may be tailored in rather detailed dimensions adapted to the existing building. However, they require usually more installation work on building site compared to pre-fabricated modules. Post and beam are usually better for larger buildings. Pre-fabricated modules allows more of efficient pre-production in a factory but may require more framing structure and a higher connection part between the existing building and the extension. This due to modular systems tend to have more standard sizes which is not adapted to the existing building. In total, it is usually possible to achieve effective and aesthetical vertical extensions with timber building systems.

Traditionally, product development concerning acoustics in the building industry is measurement oriented. For lightweight floors, frequencies that are lower than the frequency range for heavy concrete floors are an issue. The frequency range of from 50 Hz down to 20 Hz influences the human perception of impact sound in multi-story apartment buildings with lightweight floor constructions, such as timber floors, for example. It is well known that a lower frequency range of interest makes finite element simulations more feasible. Strategies for reducing impact sound tend to be less straightforward for timber floors because they have a larger variation of designs when compared to concrete floors. This implies that reliable finite element simulations of impact sound can save time and money for the building industry. This study researches the impact sound transmission of lightweight timber floors. Frequency response functions, from forces on excitation points to sound pressure in the receiving cavity below, are calculated. By using fluid elements connected to reflection-free boundary elements under the floors in the models, the transmission and insulation can be studied without involving reverberation. A floor model with a hard screed surface will have a larger impact force than a softer floor, although this issue seems less pronounced at the lowest frequencies. To characterize floor surfaces, the point mobilities of the impact points are also calculated and presented. The vibration and sound transmission levels are dependent on the selection of the excitation points. © The Author(s) 2020.