As a general contractor specializing in prefab-timber construction, we work closely with architects and planners daily. It gives us chances to communicate with each other and to address potential issues at an early stage of the projects.
1. Does timber construction have constraints on architecture? What should we consider in ad-vance?
The architectural design of a building project defines its individuality and reflects the thoughts and requirements of users and architects. This principle remains the same in the timber constructions, for example, there’s no so-called “standardized column classification” in the timber construction, and instead, we always develop project-specific solutions to support architects to realize their designs.
When comparing to concrete and steel constructions, modern timber constructions do have some different features that need to be integrated into the architectural designs, better at an early stage. The goal is to find out the optimal solutions and system based on the thorough consideration of all the key factors, including spans, riser zone, building energy standard, interior surface, etc. Our experience has shown that early involvement of timber construction experts can prepare the project team in advance and build a solid foundation for the design and planning to ensure an accurate and efficient realization of the projects.
The fast-evolving technological development in the timber construction industry has kept pushing the limit in the timber architecture and changing the perceptions of typical timber buildings. The new Vidy Theater Pavilion in Lausanne is a good example: the construction is reminiscent of Japanese origami art, in which the folds alone, without any fixings, provide the statics. It is not only a striking architectural design but also a masterpiece of engineering. In the residential and commercial sector, we also see a variety of timber architecture applications worldwide, in particular in low- to mid-rise buildings.
2. Is timber construction cheaper or more expensive than conventional concrete construction? Is it possible to have a per-square-meter price from the general (or turnkey) contractor?
Well, to answer this question, we first need to make sure that we are comparing apples with apples. Many factors affect the cost of a building project, not only the building material and construction approach but also other requirements like quality standard, building energy efficiency, room sizes, etc. Both concrete and timber construction approaches can realize building projects with either higher or lower budgets.
Our experiences have shown that, comparing to conventional concrete construction, the additional or reduced costs of timber construction range from 0 to 5% (accurate cost estimation must be conducted based on project-specific analysis). However, if we consider the lifecycle that includes the production of building materials, construction, maintenance, dismantling, disposal, and recycling, the cost of timber construction is usually cheaper.
The key to cost-effectiveness is the correct planning: if a building has been designed to be in concrete, it will be costly to convert it into timber construction. Therefore, we recommend architects and building owners/investors decide the construction system, either in timber, or concrete, or hybrid structure, at the beginning of the planning stage.
Theoretically, one could offer the per-square-meter price for a building. However, we would not include the ancillary services cost, which is usually not project-specific, such as crane, transport, site access, etc. To provide accurate cost estimation for timber construction, we must consider many important factors, such as size, complexity, building static, etc. Our engineers in the cost estimation department would be glad to discuss with you about your project.
3. How long can wooden façade cladding last? How often should the post-treatment be applied to the treated wooden facade?
Many factors have decisive influences on the maintenance of the wooden façade and the post-treatment interval. In principle, you can assume an interval of approximately 5 to 10 years. Correct planning and execution, necessary regular checks and maintenance can avoid damages that could potentially impair the wooden façade cladding. Many factors have significant impacts on how long the wooden cladding can last, including the type of wood, the surface treatment system, and the correct detailed design (the distance to the ground). Besides, the correct maintenance can prolong the service time. The input from experienced experts can help meet the various requirements of building owners at different projects.
The interval of post-treatment of treated wooden façade depends on the specific project. Also, to meet the practical requirements such as weather protection, it should fulfill the design elements. Besides, other factors like the location and direction of the building, the surroundings, and the protection of constructive wood all play important roles. In principle, you can assume an interval of approximately 5 to 10 years.
4. Is it necessary to have vapor and/or airtight layer?
Firstly, it depends on the construction type. For example, a vapor barrier is not indispensable in the diffusion-open construction. The building superstructure in each project must be planned, tested, and approved by the building physicists.
The airtightness of each building must follow the regulation of local building codes, for example, the SIA Standard 180, in Switzerland. The airtight layer can prevent energy loss that could be caused by the outwards flowing of indoor air and inwards flowing of outdoor air through the structural joints and connections in the exterior skin. Therefore, all connections must be airtight and connected through the correct planning and realization, including windows, doors, electrical installations, etc. It is critical to meet the building energy standard and to avoid any structural damages.
The combined vapor layer is also common in practice, for example, by using the same material. It does not only prevent moisture penetration but also provides thermal insulation, and avoids the condensed water in the insulation.
More questions about timber construction?
If you have more questions, please do not hesitate to contact us. We look forward to supporting you at your projects.
Photos: Ilka Kramer, Lausanne; Zeljko Gataric, Zürich