Stavneblokka – Upcycled timber bricks for the Future
Anne Sigrid Nordby outlines the original Trondheim based research project that developed the Stavneblokka reclaimed wood building system long before the Circular Economy was being talked about, and which has taken further steps in a major pan-Nordic research project
Working together with employees from Stavne and NTNU and Sør-Trøndelag University College students and staff, the primary result were two block types produced in 2010 at Stavne Rebygg, which supplied components for two small pilot projects. The first was an interior wall, forming a part of a meeting room for an open office area, while the second project was a “quiet room” within an office for Atelier Ilsvika.
1 - Up-cycling of reclaimed wood
Basing the reuse on upcycling reclaimed wood was central to the project. Our initial 2009 research on reclaimed and reuse/incineration use across Trøndelag found there was plentiful supply with up to 15 000 tons processed annually, and expected to grow on a national basis (3). Today, there is more available wood waste than can be used at regional incineration plants, with some additional waste transported to distant Norwegian regions and to Sweden. An agreement with the recycling company Franzefoss was made, enabling free access to reclaiming wood from their plant, as well as helping the Stavne Work and Competence groups and NTNU architecture students collect scrap-wood from their plant.
The research focused on developing relevant waste material uses, which would also achieve environmental benefits such as reduced GHG emissions. Although well understood and documented (4)(5) efficient material use, through reduced production related emissions and prolonged lifecycles, contrast with the general trend of measures for climate mitigation for buildings, which are primarily focused on legislation and fiscal measures aimed at improving operational energy efficiency. As a result, often outsiders’ first questions concern the U-values of the blocks and it has appeared unusual and even provocative that the Stavneblokke project’s primary goal isn’t focused on energy efficiency. Indeed, one, if not the primary, goal has been designing a usable block for low-energy housing, with analyses of the blocks overall environmental efficiency in both production and operation phases pursued.
The question is how to evaluate the environmental efficiency of this building material. It is clear that the system boundary for such an analysis is essential to accurately estimate targets such as carbon emission factors. Given biomass sequesteres carbon when growing making carbon storage in wood is real, our research argued Stavneblokka are carbon negative even if it is generally not considered in building materials assessments (6). Stavneblokka’s carbon reduction effects based on upcycling, and their potential use through several generations of building presupposes long-term management and a design that facilitates reuse. It is estimated that the captured carbon equals 1,8 kg CO2 per kg wood. 1 m2 of wall correspondingly stores an amount of carbon equivalent to 150 kg CO2. The block also uses some energy for production from scrap-wood, though no more than the production of whole timber, which is approximately 50 g CO2 eq. per kg (7). Compared with operational emissions, carbon storage in biomass materials could possibly outweigh impacts from heating and thus make massive wood components perform better than non-biomass constructions with far better U-values.
production measures
As already mentioned, one of the Stavneblokka research goals was to develop a building system appropriate for low-energy buildings, and developing a flexible component that could be combined with layers of suitable insulation materials adapted to various needs. Architecturally, the design challenge consists of developing a system which optimises the use of short pieces a challenge, as using scrap-wood as building material has a limited set of historic examples. In addition, a wooden block wall will tend to resemble brickwork more than conventional wood constructions, such as logging or wood framework, which employ longer pieces.Tectonics at a structural level, that considers the design's technological parameters, may also be relevant, including material properties, and structural and production conditions (8). Further, the Stavne timber block assumes familiarity with the waste hierarchy, and that reuse is more environmentally advantageous than recycling. If the challenge of reuse rather than recycling is taken seriously, the tectonic problem of converting small pieces of scrap-wood into novel building components can be related to the development of building systems in other waste materials as well.
Traditional materials that fit into the 19th century architectural theorist, Gottfried Semper’s two wall and frame categories, were typically wood or bamboo for the frame, and bricks or mud for the solid wall (9). The original prototype Klimablokka was considered as a solid wall, taking care of both structural and heat insulating properties. In the redesign process, however, priority has been given to a leaner component that, both structurally and regarding heat insulation, is more dependent on secondary members and layers. Thus, the new prototype is, according to Semper’s definitions, geared towards constituting a frame rather than solid mass.
First Wall
Discussion of how the block meets the various demands of the functions of the wall have been essential, even if it has been problematic designing according to a fixed scheme of criteria. Since wood is used for a range of different functions including structural purposes, thermal insulation, hygroscopic control, for interior and exterior finishes, as well as for storing carbon, choosing the right re-used wood can be decisive. We therefore asked, paraphrasing Louis Khan’s famous formulation(10); “So what do you want to be, scrap-wood?” This helped in contemplating on the block’s inherent material properties.
The ideas for the block were manifold, with general design criteria placed under four headings; Life cycle design, User needs, Material properties and Production line. Two objectives were regarded as particularly relevant for the redesign. Firstly; smaller dimension of the block, and secondly; easily accessed flexible joints. An additional aim emerged; ensuring the block design also utilised the component’s potential for architectural articulation, after several iterative design exercises highlighted prioritising the primary objectives, while builders enquiries about using the block spurred the need for practical manufacturing processes and design detailing. The pilot commissions helped us arrive at a testable block design, which was then retrospectively evaluated.
The redesign goals are now discussed in more depth.
I - Life cycle design or salvageability of building components, addressing design for reuse and recycling as well as adaptability once in use. Relevant criteria to achieve this are: Limited Material Selection, Durable Design, High Generality, Flexible Connections, Suitable layering and Information and Access5. Also, after the components last service life, the blocks should be suitable for heat recovery in standard wood-burning stoves.
Limited material selection is a basic principle for both the original and the redesigned block. Wooden boards fastened with wooden dowels make up a mono-material component without glues or metal fasteners, suitable for recycling and heat recovery. In addition, the block is designed with flexible connections to facilitate reuse. By changing the outer dimensions, the prototype was improved by adapting it directly to the 6M (600 mm) Norwegian norm.
After several radically new block designs, the final concept for the pilot projects was closer to the original type based on cross-laid boards, although unlike the original Klimablokk, the new blocks have tongue and groove connections between the blocks. This measure enabled independence from other fasteners, assisting demounting the blocks after use without damaging the connections. Stabilisation of the wall is achieved through stacking the blocks in a herringbone-pattern so that long gaps between rows of blocks are avoided. However, the structure becomes dependent on a closing frame for locking the system. Thus, the goal of flexible joints is achieved, but the joints are not visible and easily accessed.
II - User needs - Unlike large-scale and often custom-made contemporary massive wood components, the Stavneblokka system aims at easy handling of small units and suitability for self-building. It is thought that the new block is better suited for self-building than the original, due to reductions in size and weight from approximately 26 kg to 15 kg. The blocks can also be stacked in various patterns that adapt to different spatial situations and result in different visual expressions.
Other user aspects regarded economic feasibility as well as low energy demand for heating, and easy maintenance and flexibility during reconstruction. Since the new block’s additional tongue and groove system is more complicated to produce production labour and thus costs increases, although if it is also more flexible. Originally the existing thermal insulation requirements were meant to be met by single layer blocks with only a complementing layer of fibreboard sheeting and aerated cladding. However, the new block can more easily adapt to different interior and exterior wall requirements, including different thermal standards. Finally, both the original and new block perform equally well regarding ease of maintenance and flexibility for remodeling.
III - Material Properties focuses on wood being used in the best possible manner including optimising wood’s technical properties relating to shrinkage/swelling, moisture transport and structural strength. The redesign process enabled assessing different block designs, while also clarifing the benefits of the original block. This included the cross laying of boards preventing large movements caused by shrinkage/swelling, the dowels helping keep each board in place. Furthermore, when the heat transfer from inside to outside is perpendicular to the fibres, the thermal insulation property of the wood is at its best11. In both the original and the new design indoor air quality will benefit from the hygroscopic capacity of wood which, as long as not covered with impermeable varnishes or paint, will regulate air humidity.
IV – Production Line at Stavne Gård, focused on work adaptation. The blocks need to be suitable for uncomplicated, local production and be designed sensitive to ease of handling, transport and storage.
Some difficulties were on the pilot production. The tongue and groove of each block required careful sorting of boards of different dimensions, so that three layers of boards could make up exactly the dimension of the offset core piece, a labour-intensive job, and also often requiring grading of some of the boards. The offset tongue and groove made the dowelling more complicated because the dowels had to meet each layer of boards, while also not hitting too close to the board end. While the original Klimablokk’s simpler shape was unproblematic the leaner new block’s advantages, with its shorter dowels, is that it should be easier to insert. Also, as the new blocks were prepared in custom-made frames, there was no need for extra pressure before dowelling.
V - Further potential design improvements were proposed after difficulties in producing a uniform tongue and groove core of the block. These include a core of single 2 inch pieces rather than three layers of cross-laid boards, and sourcing boards as ‘stubs’ at building sites instead of reclaiming waste wood from recycling plants. Stubs contain fewer nails and other metal pieces and their need removal easing preparation of the boards before manufacturing. In general, it is believed that it would be beneficial if material supply and design were brought closer. This means that each series of blocks could be designed according to the available dimensions of the boards.
Conclusions
The Stavne timber block project is motivated by finding relevant and innovative use for wood waste, which is abundant across Trøndelag. Climate mitigation is achieved through low-impact material use and processing, lifecycle design and through carbon storage. Re-use is prioritised over recycling and incineration, in line with waste hierarchy thinking. The redesign process investigation of the component identified some advantages and some challenges compared with the original prototype Klimablokken. Firstly, new dimensions and lighter weight of the block give higher generality and eases handling for self-building. Secondly, the tongue and groove system enables flexible joints, which facilitate reuse, although joints remain difficult to access, and the closing frame is not ideal in the context of remodelling. Thirdly, the new block is considered to have greater architectural flexibility, specifically in the variety of different interior and exterior walls that the blocks can constitute, either as a separate layer or combined with insulation, sheeting and cladding. Also, in terms of visual expression, the new block is flexible for use in various patterns, adapted to the context.
In the two pilot projects, the Stavne timber block system was used for constructive purposes in different ways. In the Svartlamon wall (5m x 2,4m), the framed blocks did not structurally support the balcony room above, but acted first of all as an eye-catching interior finish. In the ‘quiet room’ in Aterlier Ilsvika, the two main walls (2,1m x 2,1m) worked as load bearing frames set on wheels. Particular attention is paid to noise insulation, gaps between blocks and between the other building parts, which were insulated with strips of cellulose fiber. In both projects, the wooden blocks function as means for hygroscopic control of the indoor air, as well as for storing carbon.
The inputs across the project network gave invaluable information and inspiration, not least for HIST employees and NTNU students. New ideas developed after the original, self-building system for exterior walls of dwellings concept. These included sheds and cabins with no thermal insulation, and other exterior uses such as windscreens, noise barriers and outdoor furniture where reusability could be emphasised.
Commercialisation has been a background aspiration. The blocks labour intensive production process remains an important concern, although different time-saving measures have been proposed. The Stavneblokka has, maybe more importantly, provoked reactions regarding its fundamental scopes and aims, and the project can be seen as an arena for discussion and dissemination as well as a provocative statement. The Stavne timber block questions the ways in which the building industry operates, and point to alternative ways of reasoning about environmental priorities.
This is an edited version of a research paper by Anne Sigrid Nordby on the Stavneblokka project, which was live between 2008 and 2010. The Stavne Rebygg salvage yard closed down in late 2010, which brought a halt to its production. However the two pilot prototypes continue to be in use.
The paper builds upon work experience, discussions and ideas belonging to the project team, which in addition to Anne Sigrid Nordby, consisted of project leader and industrial designer Kristin Støren Wigum at Gaia Trondheim and section leader Kenneth Urdshals at Stavne Rebygg. The project was financially supported by Innovasjon Norge (Innovation Norway), Framtidens byer (Cities of the Future) and Husbanken (the Norwegian State Housing Bank.)
Anne Sigrid Nordby’s research and consultancy has continued and is now part of the multidisciplinary consultancy company Asplan Viak. In a collaborative project led by Tegnestuen Vandkunsten 2014-2016 Nordic Built Component Reuse, similar ideas as for Stavneblokka were pursued for a greater range of building material waste fractions.
1. Bjørn Berge, Klimablokken,Gaia Lista (2006).
2. Kristin Støren Wigum, Anne Sigrid Nordby & Kenneth Urdshals, Gjenbruk av byggematerialer og
komponenter – betingelser og muligheter. Stavne/ Gaia Trondheim (2009)
3. Rannveig Ravnanger Landet, Nasjonal handlingsplan for bygg- og anleggsavfall (NHP) 2007-2012 (2007). Available from www.byggemiljo.no
4. Bjørn Berge, Ecology of Building Materials, Architectural Press (2009).
5. Anne Sigrid Nordby, Salvageability of building materials, Thesis, NTNU (2009).
6. Eric Johnsen, ‘Goodbye to carbon neutral: Getting biomass footprints right’, in Environmental Impact Assessment Review 29, pp. 165-168, 2009.
7. Eivind Selvig, Klimagassregnskap for utbyggingsprosjekter. Civitas/ Statsbygg, Oslo (2007).
8. Anne Beim, Tektoniske visioner i arkitektur. Kunstakademiets Arkitektskoles Forlag, København (2004)
9. Kenneth Frampton, ‘Rappel à l’Ordre: The Case for the Tectonic’ in Architectural design, vol. 60, nr. 3/4, pp.19-25 (1990).
10. Referred to in 8, p. 56.
11. See 1, p. 297.