Four key classifications

There are four basic fire safety classifications for structures and one classification specifically developed for timber structures. The first deals with ignition and fire spread on the surface of the structure, sometimes referred to as 'reaction to fire'. This classification can be used to select appropriate finishes in escape routes, for example, to minimise the risk of rapid fire spread that could impede evacuation. The extent to which a finish or building product contributes to the development of a fire when installed on both the walls and ceiling of a standardised room is the starting point for the classification. Exposed wood in escape routes must be treated to ensure a sufficiently low risk of ignition and fire spread.

The second classification concerns the fire resistance of the structure. It classifies the ability of a structure or building component to maintain its function when subjected to a standardised fire exposure. The standardised fire exposure is called the standard fire curve which can be seen as a kind of simplified representation of a fully developed fire in a room. The standard fire curve is simulated using fire test furnaces. After testing, the structure receives a classification where the most common classes are R the load-bearing capacity, E the integrity and I the insulating capacity. The different classes are always followed by a time indication, for example, when a wall that does not carry any load has the class EI90, it means that it encloses and isolates the standard fire for 90 minutes.

The third classification, the so-called K-class originally developed for timber structures, relates to fire resistance. The classification indicates how long a protective layer protects the structure from ignition at the standardised fire exposure.

The fourth classification refers to the resistance of the façade structure, including any air gaps, to vertical fire spread. This property is tested in a facade rig where a 6 metre high and 4 metre wide facade is exposed to flames emanating from a window during a fully developed fire in a room. The classifications of finishes, structures and fire resistance can be determined using standardised fire tests. The fire resistance class can also be determined by theoretical calculations according to the instructions in the common European construction rules, the Eurocodes. We therefore have a common European system for both classifications and theoretical calculations, but each country decides which requirement level should apply nationally. Only the fire classification of facade structures is done according to national standards.

Achieving robust fire protection - more than just classifications

A common approach to meeting fire resistance requirements is to use different types of protective layers such as plasterboard to form a protective membrane that delays the spread of fire, protects the supporting structure and prevents fire from entering hidden spaces in the structure. All installations, penetrations through the membrane and all connection details between elements must be fire rated, designed and installed correctly as they could otherwise jeopardise the performance of the protective layer. A German study (from 2006 for different types of houses) showed that 50 % of the installations inspected in the study compromised the fire protection membrane. During the lifetime of a building, there is a risk of damage to the fire protection membrane, for example through holes from removed or new installations. If there are combustible materials behind the protective membrane, the risk of a possible fire continuing and spreading in the timber structure increases.Post-extinguishing in structures where the fire has spread through the protective membrane to the timber frame requires more effort than in completely non-combustible frames.

Experience from previous high damage fire incidents shows that improvements to a few strategic details would have significantly reduced the spread of fire A robust and well thought-out fire protection strategy that stands the test of time is an important step in the sustainability and insurability of timber multi-storey buildings. A strategy to keep track of all important details should be the first step for the whole industry.

This is an article from our magazine Trävärden, view it here! (Link)

Roofing with rafters provides a stable base for roofing with roofing felt, tiles and sheet metal. The use of prefabricated underlayment shutters allows for faster roofing. The unprotected roof surface and building are exposed to climate and external influences for a shorter time, reducing the risk of future problems in the finished building. Prefabricated underlay shutters produced in a controlled production environment provide the conditions for consistently high quality.

A type approval for the manufacture of underlayment shutters allows you to demonstrate that the product has been manufactured under controlled conditions and fulfils the requirements for its intended use, giving you a competitive advantage. The certification rule for a product describes the certification process when applying for a type approval, the requirements, checks and labelling to be done for the product. To minimise the risk of different interpretations, the certification rule for the type approval of underlay shutters was updated in September 2023.

Type approval of manufactured products is done by an authorised independent party. Boverket has appointed RISE as a competent organisation to issue type approval for construction products and accredited by Swedac for it. Type approval of underlay shutters is unique in the market and RISE is the only organisation that can issue type approval, perform accredited inspection and offer accredited testing of all the properties included in the certification rule for underlay shutters. 

RISE develops certification rules for type approvals and certifies product type approvals.

When RISE develops new rules for type approval, we start from the rules and regulations developed by authorities, in this case the Swedish National Board of Housing, Building and Planning, and RISE's long experience of testing and type approval of products in the field. When you then hire RISE to issue a type approval for your product, you can be sure that an issued type approval maintains a high level and that the type-approved products meet the requirements of the building regulations. Type approval is carried out according to the certification rule through testing and review that ensures that materials, function and documentation have the conditions to fulfil, such as for underlayment shutters, applicable requirements for durability, moisture and roof safety.

This is an article from our magazine Trävärden, view it here! (Link)

The Swedish Building Regulations (BBR 18 6:52) state that well-researched and documented critical moisture conditions should be used during the design and construction period. If this does not exist, 75% RH should be used as the critical moisture condition for mould growth. Moisture levels in building components vary in different parts of a building, as different activities and premises are more humid than others. Choosing a product that has a higher critical moisture condition than the expected moisture level in the building element reduces the risk of mould growth. 

Mould growth in a building is a consequence of moisture either as humidity or the introduction of free water through, for example, water damage or condensation. If the relative humidity RF in a building section exceeds 75% at room temperature, there is a risk of mould growth on the building materials. This level is a general minimum level but not all products will grow mould at this level. This is because the threshold for mould growth on a material varies between different products. Some products can be exposed to high moisture levels without mould growing on them, while others grow at lower levels. This property is described by the critical moisture state of the material with respect to mould growth. The difference between different products' critical moisture conditions for mould growth is that they contain different amounts of organic nutrients for the moulds to grow on.

There are no standardised values for the critical moisture condition for groups of building materials. The critical moisture condition can be affected by various factors, including any additives in the material and layers on the material surface. Research shows that different products within the same material group, such as plasterboard, wood fibre board or wood fibre insulation, can have significantly different properties and limit values for mould growth. Therefore, it is impossible to estimate or guess the critical moisture condition for a product group; it needs to be determined for each individual product within the group.

The critical moisture content of a material is determined by testing the product in the laboratory in a standardised way. According to the test method, the products are tested at four different moisture levels at +22°C The critical moisture state is affected by temperature and if it is colder, more moisture is needed for mould to grow. The method includes an equation to calculate the critical moisture condition at temperatures other than the constant temperature of +22 °C used in the test. It is important to point out that the critical moisture condition of a product is not a measure of how good or bad it is. Instead, it is an aid to making informed decisions on the choice of materials for building elements where the moisture level is known. To reduce the risk of mould-related damage in buildings, more actors in the industry would need to recognise the importance of using critical moisture conditions in the design of buildings. To facilitate this work, more material manufacturers need to choose to test and report the critical moisture condition on their products.

This is an article from our magazine Trävärden, view it here! (Link)

The environmental impact of the built environment and the construction industry is huge due to the extensive use of energy and resources. To change this, the transition to a circular economy is one of the key approaches to sustainable development and the solution to its environmental impact. A newly launched project DUET - Circular Design and Use of Wood Building Elements will increase the resource efficiency of wood use by studying the technical feasibility of using recycled wood and/or industrial wood waste together with new wood to produce new building elements for load-bearing walls and floors.

Using both recycled materials and/or residues can facilitate the manufacturing and market acceptance of the new products. The project studies both technical and environmental feasibility, but also the possibility of circular use of the new building elements. A future circular use means that the building elements will be easier to dismantle and reuse as elements or in parts for recycling of the sub-materials. This increases the lifetime of the building elements and helps to significantly extend the time of carbon storage and thus the strategies and targets for net zero emissions in society.

The development work with regard to material flows is done in co-operation with Forestia and Gällö Timber AB. The circular use of wall and floor elements is developed in collaboration with IsoTimber Holding AB and Masonite Beams AB. In the project, prototypes for wall and floor elements will be built and tested to verify that the technical and mechanical requirements for building products are met.

This is an article from our magazine Trävärden, view it here! (Link)

Building with wood is an opportunity for the construction industry to reduce its negative environmental impact. Interest in building with cross-laminated timber, or CLT as it is called, is growing even among builders who have traditionally used other materials. Developed in the mid-1990s in Central Europe, CLT is a wooden board glued together from sawn, strength graded boards (usually spruce). The structure of CLT boards with crosswise layers of boards means that the strength and stiffness of the board is largely equal in both directions in the plane of the board. In load-bearing structures, this property is not always the most optimal in terms of utilisation of the material. This means that relatively large amounts of wood raw material are required when building with CLT. In today's CLT, high quality timber is often used in all layers of boards. However, using the same type of timber in all layers makes the production process easier to handle than using multiple wood qualities, species or changing the direction of the layers of boards in the panel.

Since the players who manufacture and build with CLT use high quality timber, they are more affected by the availability and increased prices of wood raw material compared with manufacturers and suppliers of other timber construction systems. The effect of price increases is reduced competitiveness in relation to other timber construction systems available on the market. For Sweden, global warming may mean longer periods of drought or longer periods of abundant rainfall, which will change the conditions for forestry and the choice of tree species. In such a future scenario, it becomes more interesting to look at optimised solutions to change the design of today's CLT products.

Building with CLT
Building with CLT is similar to conventional construction with prefabricated concrete elements. Customised building elements are manufactured in the factory and adapted for assembly on the construction site based on design drawings. The size of the CLT panels is limited by production capacity and full-sized panels are cut to exact dimensions and customised with holes for doors, windows and wiring according to the customer's wishes. These customised board elements are then assembled at the construction site to form the load-bearing frame of the house and are then completed with insulation and façade systems on the outside and often with plasterboard on the inside. CLT panels are stable and self-supporting and with few types of structural elements the load-bearing frame of a house can be built. The relatively low density of the wood material compared to concrete means that more building elements, a larger volume, can be lifted and transported in the same transport. This contributes to better shipping and lifting logistics in the construction phase, which in turn contributes to better overall project economics. Good dimensional stability together with good workability makes it possible to manufacture elements with exact dimensions and small tolerances, another advantage over conventional construction with concrete. Building with CLT is also perceived as flexible because it is easy to use simple tools to make adjustments and drill holes etc. both in the factory and on the construction site. The production-related disadvantages of CLT are that wood as a material is sensitive to moisture and there is therefore a risk of microorganism growth. Measures to manage moisture throughout the construction process are a factor that can make construction more expensive than conventional construction with other materials such as concrete. As a rule, a CLT frame is supplemented with surface layers on the construction site, and the work of completing the facades of tall CLT buildings tends to be resource-intensive and inefficient, as scaffolding is needed and insulation and facade materials are installed at various stages. The work can be protracted before a complete climate shell is in place.

Looking to the future - resource efficiency
At RISE, a future exploration has been carried out together with researchers and actors from the value chain for construction with CLT. Proposals for how a future resource-efficient CLT product could be designed, how production can be carried out and how it can be designed were discussed. A summary of the proposals is presented below.

Raw material for CLT
There is potential for improvement to become more efficient in the use of raw materials by developing the logistics from the forest to the manufacture of CLT panels. In the forest, this may involve investigating which stands in the forest are suitable for use in the manufacture of CLT, selecting the timber already in the forest and optimising for more or fewer varieties of tree species. With regard to the CLT panel as a final product, start optimising the use of the timber against current orders for CLT panels. In order to reduce the costs of producing panels, the availability of raw material and the use of lower quality timber need to be investigated. Specifically, it would be possible to investigate the advantages and disadvantages and the possibility of using timber that is currently used for paper and pulp and firewood in the manufacture of CLT, but also whether changes to the cant rules could enable the use of timber with cant in the centre layers of CLT panels. In order to create incentives and evidence to increase the use of CLT, environmental impact analyses need to be developed to assess how the use of an increased proportion of lower quality wood in CLT panels, which are long-lived products, can increase the overall effect on carbon sequestration compared to using lower quality wood for short-lived products, such as packaging material or energy.

CLT as a material
With regard to the properties of CLT panels, a development is desired to adapt the structure of the panel to the final panel's use as a structural element in the building. The possibility of concentrating materials with good load-bearing capacity in the parts where loads are to be transferred and fixings made. Reinforcement in those zones possibly also with other materials such as LVL, which is stronger than ordinary timber. However, the parts of the CLT panel that are not to carry loads or where windows and doorways are to be located, inferior and/or smaller amounts of material can be used.

Building with CLT
In a desired future situation with regard to building with CLT, it would be desirable to see a wide range of skilled contractors who know about and build with CLT. Economic evidence that it is profitable is needed for more people to start building.
In order to increase resource efficiency with regard to the use of wood raw materials, greater knowledge is needed about where CLT is most useful in a building structure so that CLT panels are used in the most efficient way. This could mean, for example, combining different building systems with CLT to create hybrid structures using both other wooden building systems and other materials such as concrete and steel, such as a combination with concrete floors on a load-bearing CLT frame. Development of frames where the load-bearing capacity of the CLT panel in both directions would be utilised to a greater extent. One such advanced example is column decks in CLT that would provide new design opportunities for architects who want open spaces. Ongoing development that would need to be done is the development of load-bearing joints between CLT panels and column tops and foot connections that can handle high loads.

In a desired future situation, assembly and carcass completion on the construction site also needs to be more efficient. There is a need for a greater degree of customisation, processing and prefabrication in the factory for future assembly on the construction site. This requires the development of joints and connections to ensure high precision and speed of assembly. Frame completion with windows, doors, insulation and facade materials needs to be rationalised, to reduce the time between erection of the frame and a tight house. Carcass completion inside the house also needs to be rationalised, for example, apartment separating floors currently require many different work steps to be completed. In addition, maintenance of the built environment needs to be done cost-effectively and with sustainable materials. To future-proof construction, circularity and reuse - being able to dismantle and reassemble buildings - must be possible. RISE's offer in the field of CLT includes testing and/or calculation for verification of product properties, product certification (CE marking or type approval) and inspection.

Further reading
This article is based on the report The future of CLT from a project conducted at RISE and financed by RISE, Swedish Wood and TMF Trä- och möbelföretagen.

This is an article from our magazine Trävärden, it is available in full here! (Link)

In 2020, the country's 4333 wind turbines produced 16% of our energy in Sweden (Energi myndigheten 2020, Ny statistik över installerad vindkraft 2020 (energimyndigheten.se). That's a lot of power plants and more are expected in the coming years. They produce renewable energy, but also contribute to greenhouse gas emissions. In general, today's wind turbines are built with materials such as steel and concrete. Strong materials that can withstand the forces a wind turbine is subjected to, but the traditional choice of materials contributes to high greenhouse gas emissions. The largest contributor to the climate impact of wind power comes from the raw materials used in the manufacture of the turbines.

The wind power industry has a need to reduce the climate impact when manufacturing new power plants. The Gothenburg-based company Modvion is helping to reduce the climate impact of the wind power industry by replacing the tower, which is usually made of steel, with a wooden tower of the same height. In 2020, the first 30-metre-high wooden wind power tower was erected on Björkö in the Gothenburg archipelago. Another tower was recently erected in Skara, reaching 105 metres. Subsequently, even higher towers are planned to support turbines with even greater production capacity.

Advantages of wooden wind towers
Wood is a renewable material that also sequesters carbon over the life of the wind turbine. Steel is strong - stronger than wood - but it is also heavy. When comparing the strength of materials in relation to their weight, wood outperforms steel. In increasingly tall towers, the weight of the tower means that the steel tower needs to be reinforced to support its own weight. Wooden towers, which are lighter, do not have the same problem with their own weight and so it is possible to build tall and slender with wood. To cope with the extreme forces of the massive rotor blades at the top of the tower and the strong winds to which a wind turbine is exposed, Modvion has developed and now manufactures wooden frames for wind towers. The construction consists of thin wood laminates that are glued and pressed together into curved 15 metre long wooden modules. The modules are erected, joined and then stacked on top of each other to erect the tower. The relatively small size of the modules allows them to be transported to the construction site by smaller lorries compared to today's steel towers where specialised vehicles are used to transport larger components.

Development work
One challenge has been to develop strong joints for joining the modules that can be efficiently assembled on site and withstand the extreme forces on the tower. The solution used is inspired by a relatively new technique where a steel plate with holes is glued between the wooden elements to be joined. This differs from traditional jointing solutions where steel plates are used in combination with, for example, screws, bolts or dowels. Using glue instead of metal connectors results in very strong and rigid joints. The manufacture of glued wood structures is usually done in a factory in a controlled environment and under controlled conditions. On the construction site, temperature, humidity and working conditions vary and thus it can be difficult to control the quality of the gluing. In the project Stuck in the middle with you (SIMWY), funded by Vinnova, Modvion, Henkel and RISE are collaborating to develop Modvion's method for construction gluing on the construction site. You can read more about the project on the project website, (Link).

Developing new technology means that it needs to be tested and evaluated. RISE has experts in various subject areas and laboratories for testing and evaluating materials and structures, both on a small and large scale. Together with Modvion, RISE has tested the the new hybrid joint for different types of loads that mimic those it needs to withstand in reality in a completed wind turbine tower. The joint has also been subjected to fatigue through cyclic tests where it has been loaded and unloaded thousands of times over a long period of time to failure. Fatigue is rarely relevant in ordinary wooden buildings, but in structures such as bridges and nowadays tall towers that are loaded with high varying loads during their lifetime, the phenomenon becomes relevant. 

This is an article from our magazine Trävärden, it is available in full here! (Link)

Reusing materials is an important way to meet society's climate challenges and reduce waste. Leaving the linear flow of materials and creating a more circular mindset is also important in housing construction. There is a need for knowledge about how to build today in order to be able to reuse in the future and thereby save the planet's resources.

The research institute RISE and IVL Swedish Environmental Research Institute, together with 16 partners from the construction value chain, are conducting a project entitled "Future design - Reuse of wooden buildings in a circular economy". The project is developing demountable and reusable wooden buildings to increase environmental benefits and at the same time increase collaboration in the circular value chain for residential construction. The wooden buildings should be easy to disassemble and flexible to change so that they can be used for different applications over a long period of time while maintaining value and reducing construction waste. The aim is to demonstrate opportunities and systems suitable for disassembly, reassembly and reuse. 

Everyone is needed to create circular flows 

To leave the linear material flow and create a more circular way of thinking, it is important to engage all parties and build a common understanding of the interaction in the circular value chain. The project participants' competencies and experiences have been the basis for assumptions and scenarios that have then been used to estimate and simulate disassembly, reassembly, reusability and calculate climate benefits (such as waste quantities and additional new materials during construction, energy use in the factory and on the construction site). This created a common methodology that was used to simulate disassembly and reassembly on two buildings.

Two timber buildings as examples for future design

Documentation was produced for two building projects to demonstrate reusability and climate benefits from different perspectives. The building projects are Folkhem's planned construction of five new residential buildings in the Klockelund block in Farsta and the "Flexibility House" around Kiruna and Skellefteå municipality. One building project is based on industrially manufactured house volumes and the other on plan elements from the partnership's representatives of the wooden house industry. 

Demountable and reassemblable wooden building with industrially manufactured volumes

The Folkhemmets building project is a planned building in the Klockelund neighborhood in Farsta. In the project, a dismantling plan was developed with instructions for information management for dismantling construction with volume elements. The plan describes steps for dismantling such as securing walls and floors for fire and strength, details for dismantling installations, joints, lifts, balconies, stairs, attics, roofs, facades and lifting of roof and volume elements. There is great potential to reduce the climate impact when reusing industrially produced wooden volume elements. The climate impact was calculated using LCA (life cycle analysis) for the product phase (A1-A3 in the standard), the construction production phase (A4-A5) and the final phase (C1), which includes dismantling and demolition.

"Flexibility House" a flexible timber building with reusable plan elements 

The great need for housing in a changing housing market in the north presents both short-term and long-term challenges. Many homes are already being built today with simple modular solutions for incoming entrepreneurs and students, but to attract skills and labor, attractive living environments and services are required. Based on this challenge and the need to respond to the constant changes in society, the concept of the 'Flexibility House' was developed. It is a flexible dismountable building that can be modified, moved and added to as needed, adapting to its context and enriching the site on which it stands.

The aim is for the Flexibility House to save resources in all phases of its life cycle and thus have a low climate impact. The climate benefits of reuse are significant in both projects, with the advantage that it is already possible to reuse industrially manufactured volume elements. Reuse is facilitated by the industrial production because all information from the design is available, which the manufacturers of volume elements Derome, Lindbäcks Bygg and OBOS confirm.

The buildings developed according to the method of the Future Design project can already be ordered today, but it is important to contact the suppliers at an early stage of your project to increase the accuracy of what you want and to ensure that both design and construction are efficient.

This is an article from our magazine Trävärden, view it here! (Link)

Taller buildings with timber frames are still uncommon, although examples as high as 20 storeys can be found in Sweden, but buildings up to eight storeys are very widely built. Building high, regardless of the materials used, poses some new challenges compared to building lower buildings. Challenges drive the development of construction in timber, which benefits construction in general for the industry.

For high-rise timber buildings, the challenges are mainly related to stabilisation, fire safety and production aspects. The "High-rise timber buildings" project has established that it is entirely possible to design and build 22-storey buildings with a timber frame that meet the requirements for stability, vibration and fire safety. Two critical aspects were fire safety and the risk of movement caused by wind loads at the top of the building. RISE and the consulting companies BRIAB and Brandskyddslaget have developed guidelines for fire safety challenges that have been developed to support similar design processes. Wind-induced movements proved to be a challenge already at 10-12 storeys, but became manageable even for 22-storey buildings with the help of related projects. The magnitude of wind-induced movements depends on the weight, stiffness and damping of the building, but due to the few other examples of tall timber buildings, there is great uncertainty as to how large the damping can be. To increase the understanding, it was studied in a European co-operation project, with RISE as coordinator, by evaluating the damping in eight large timber buildings in Europe.

In Sweden, Linnaeus University and RISE carried out measurements in a building in Mariestad to evaluate the properties of the building with respect to wind load. Results from the project will be summarised in recommendations for how calculation models for wind load of tall buildings should be designed to best describe the actual load. Funding Formas, Vinnova, Energimydnigheten and ForestValue.

Further reading
Tall timber buildings - concept study (Link)

This is an article from our magazine Trävärden, view it here! (Link)

We face a major need for renovation, especially of buildings constructed between the 1950s and 1990s. From a societal perspective, it is important to improve the building stock by extending its lifespan and updating it to current energy requirements. In renovations, additional insulation is a common measure that often negatively affects the aesthetic appearance of the façade. This means an operational gain but often a loss of the original design. In a previous project Fasaden i Staden, Snabb, Snygg, Smart (financed via BioInnovation), led by RISE Träbyggande, an innovative wooden façade system was developed for new construction in the urban environment.

Through the project "E2B2 Climate-smart renovation with innovative wooden facade (funded by the Swedish Energy Agency), it is possible to save energy by continuing to develop and adapt the facade system to the renovation of million program buildings.

-In addition, the facade system will be designed with a focus on an adaptable and digitalized design process, and the components will be possible to dismantle in the future, says project manager Karin Sandberg, RISE. 

The façade system should also be designed so that it can be manufactured in the factory and then easily assembled on the construction site.

-Case studies will be used to verify how well the façade system is designed for manufacturing, LCA energy optimization, digital management of information and variation in design possibilities for the architect. The result will be presented in a digital platform model, says Camilla Schlyter, RISE, who works as the institute's doctoral student on the issue.

The aim of the project is to ensure that the entire chain from design to production works in practice. Prototypes are being manufactured by the project partners Hedlunda Industrier and SCA with Kiruna Bostäder's renovation of Lombolo in mind, and Equator Arkitekter is contributing design expertise.

-We see an increased demand for facade systems that are climate neutral and optimized for low material and energy consumption, and provide the opportunity for aesthetic freedom and variation for architects, developers and managers, says Camilla Schlyter.

-The project contributes to the development of attractive bio-based facades central to the transition of the civil engineering industry towards a reduced fossil dependence, concludes Karin Sandberg.

This is an article from our magazine Trävärden, view it here! (Link)

The Swedish sawmill industry is very dependent on spruce and pine, so RISE has now produced documentation showing how two "new" types of wood could be used in structural applications. The wood species are birch, which is Sweden's third most common wood species, and contorta pine, which is the third most common coniferous species. Neither contorta pine nor birch has been able to be graded and CE marked for structural timber in Sweden or Europe1 before. Using more wood species could broaden the raw material base for structural timber and potentially provide higher strength classes than today. Two recent projects, BizWOOD Småland2 and Konstruktionsvirke - Contorta3 have investigated the possibility of strength grading of birch and contorta pine.

Birch as a sawn product is used in the furniture industry, but the use is currently small and is about 50,000 m3fub4. The birch, which actually consists of two sawn wood species, spring birch (Betula pendula) and glass birch (Betula pubesens), has been tested by RISE through a part of the BizWOOD Småland project. The studies show that birch has a significantly higher strength, stiffness and density than our normally used softwood species. In addition, it shows that it would be possible to sort birch with the same approach as conifers both visually and mechanically. The sorting could provide a high yield and sort out high strength classes, in classes up to C45 for construction timber.

Continuation follows and the results from the project will be co-published together with Norwegian results from tests made at RISE for NIBIO, the Norwegian Institute of Bioeconomy. A report will also be presented to CEN/ WG123/TG1, which forms the basis for an AGR (Approves Grading Report) which is an approval for grading for Norwegian and Swedish birch. When the report is published, it will be possible to grade structural timber from birch.

The contorta pine is Sweden's third most common coniferous tree species and originates from North America, where it can be found all the way from California in the south to Alaska in the north. In this vast natural range, it exists as several subspecies. The Swedish contorta originates in the inner parts of central British Columbia in Canada. Today, we speak of contorta, contorta pine or twisted pine. In its natural habitat in Canada it goes by the names. Lodgepole pine and Shore pine. Contorta pine grows quickly in the right soils in the Swedish climate, with up to 40% better volume growth than our native pine.

In the project Konstruktionsvirke - Contorta, machine manufacturers of sorting machines were given the opportunity to carry out measurements in their own machines on collected sample material. In combination with fracture tests conducted at RISE, setting values were calculated for the sorting machines. At present, one machine manufacturer has had an AGR report approved and the other participating companies have data to produce their AGR reports. Once the machine manufacturers have had their report approved, it is possible for sawmills that use sorting machines from them to sort construction timber from contorta. Results from the project show that contorta pine has both lower bending strength and stiffness than domestic pine, which was expected due to the higher growth rate. However, it should be emphasized that grading could give a high yield for strength class C16, which is good enough for many purposes.

This is an article from our magazine Trävärden, view it here! (Link)