Text: Liisa Akimof, founding partner, producer, WLT developer
Richard Sirén, founding partner, architect and WLT-design

Aaltopuu, or Wave Layered Timber (WLT®), is a Finnish glue-free innovation for mass-timber structures. WLT targets the core of today’s timber construction revolution, offering a sustainable, green, and grounded alternative to carbon-intensive concrete-dominated construction. In contrast to modern laminated massive timber solutions, WLT provides unique opportunities due to its glue-free nature, the applicability of timber raw materials, and logistical ease.The WLT technique allows the use of local wood, regardless of species, grade, or location. The patented WLT technique is glue-free, dimensionally stable, dense, and uses a composite-like element technology based on mechanical tightening.

More than ten buildings and bridges have already been constructed in Finland using WLT technology. There are also individual buildings abroad that utilise the WLT technique. The company is launching the WLT 1.0 guideline, along with a web-based database, next spring, and aims to become a licensed supplier for both the construction industry and small-scale producers. WLT has been a patented solution and a registered trademark since 2018. WLT is suitable for both DIY construction and industrial element production.

The WLT element can be assembled upright, flat, or even at an angle by stacking individual wave-shaped lamellas on a steel threaded rod. Lifting equipment is not necessarily needed for WLT construction, as the elements can be transported to the construction site in parts. Thus, WLT elements can also be disassembled, moved, and reused. The technique is adaptable to a wide range of solutions, from small to large constructions.

For designers, an exciting aspect of the WLT technique is the free-form language and technical features it enables – it can be made curved or straight, thick or long, much like Lego bricks or tiles.

WLT production does not require a large manufacturing facility; for smaller-scale production, simple woodworking equipment will suffice. In Finland, the first licensed WLT manufacturer will begin operations in Leppävirta at the end of 2024, with more to follow. As new manufacturing plants emerge, specialised manufacturing equipment and certified products will be developed to meet market needs. At this stage, it is known that WLT-based solutions intended for mass production in the construction industry can be manufactured very competitively.

In the Southern Cone region—Uruguay, Argentina, Chile, and recently Paraguay—there has been a surge in timber construction. Local softwoods like fast-growing eucalyptus and pine are most valuable as lumber, while WLT enables the use of weak and softwood species in mass timber structures.

WLT and timber construction

Finnish WLT buildings have used domestic pine, as it has been readily available and reasonably priced, but other wood species can also be used. One advantage of massive timber structures is that all parts and surfaces of a building can be made from the same material. There’s no need to consider how different materials interact with each other or how their availability may vary over time and across locations.

The so-called “low-tech” approach of the WLT technique enables the use of mixed and recycled wood species locally. This means that obtaining and processing wood can be done locally, regardless of location.

The beauty and durability of wood are part of the appeal of timber construction. With the growing population and urbanization, there is once again increasing demand for new solutions. Timber construction and wood hold great potential, and WLT could offer a clear and simple universal system for timber construction where the wood grows.

The WLT 1.0 construction system will be launched in spring 2025

WLT solutions do not yet have product certifications, and the structural adequacy is currently verified, if necessary, through site-specific approvals as part of the building permit process. WLT 1.0, the design and production guidelines, will be launched next spring, providing a comprehensive information package and database for WLT production and design. The guideline follows European standards (EN or Eurocodes) and can also be applied with other standardization systems.

The Finnish research institutions VTT and Luke have examined the carbon footprint of the WLT-built workspace located at Huopalahti station in Helsinki – the largest carbon dioxide load comes from the steel threaded rods. Through product development, efforts are being made to reduce their amount, which will lower not only the carbon footprint but also construction costs. In the future, significantly fewer steel components will be required.

WLT CAPITAL OY

WLT Capital Oy has focused on pilot projects and research on WLT technology, where various WLT solutions have been applied. Notably, a 400 m² two-story residential building called “Asuinkasarmi” (Residential Barracks) was built at the Huopalahti station area. It was selected as the second most beautiful new building in Finland in 2024 and has been featured in several architectural publications on “sustainable and beautiful construction.” Asuinkasarmi has also been nominated for the Nordic Council’s Environmental Friendly Building Award.

Other projects designed with WLT building techniques have also received recognition; last year, a housing development competition received an honorable mention in Uruguay and won in Argentina last month. The Mäntsälä Guesthouse (Pinewood Guesthouse) was selected as one of the Top 25 timber construction projects in the Nordic Council’s 2019 ranking.

Aiming for the global market

WLT Capital Oy is dedicated to developing the productisation of WLT technology with the aim of expanding into the global market through WLT production licensing.

A key part of WLT technology’s global development is a collaboration with the University of Arkansas in the United States. Under the university’s architecture faculty, the Fay Jones School of Architecture + Design and the Urban Design Build Studio (UDBS) program, three 60 m² residential houses are being built using WLT technology.

The program’s goal is to promote the use of regional timber resources and less-skilled labor, creating new jobs and affordable housing. The objective is to develop a cost-effective process for building sustainable and high-quality housing while addressing national affordable housing goals. The UDBS program is led by Professor John Folan, who works at the Fay Jones School of Architecture and Design, University of Arkansas, which is headed by Dean Peter MacKeith. Dean MacKeith has decades of experience in collaboration with Finland.

In the U.S., as in other parts of the world, there is a growing trend toward timber construction. As a result, new, more practical production and building solutions are being sought for both the construction industry and individual builders.

WLT Capital Oy is ready to expand its operations in Europe and the United States. The company is negotiating new license-based manufacturing agreements in Europe and preparing support and consulting services for new products and building projects. Collaboration with the University of Arkansas provides a strong foundation for the company’s expansion into the U.S. market.

WLT in a nutshell

• Glue-free, simple massive timber construction technology that enables the use of unclassified and softwood species in construction
• Over ten pilot projects completed, including buildings and bridges since 2018
• One licensed manufacturer operating in Finland by the end of 2024, and four internationally by 2025
• Focus on developing manufacturing techniques for scalable production, product certification, and approvals by 2025
• A web-based WLT database and WLT 1.0 guidelines will be launched in spring 2025

The company’s board and founders include Lauri Rautkari (Professor, Head of the Department of Bioproducts and Biosystems, Aalto University), Esko Kolli (Trustee of the Marjatta and Eino Kolli Foundation, Kolli Invest Oy), Ari Kolehmainen (Chairman of the Board, Flowmedik Oy), and Liisa Akimof (Producer, Musician, Developer of WLT-Asuinkasarmi).