Building elements with a high degree of prefabrication, produced in a workshop are typical characteristics of modern timber construction. While to build economically and to improve quality prefabrication is essential, it demands greater planning effort, as the production of components, their transport logistics and the assembly process must all be taken into account. For decades traditional construction methods have shaped the development of projects and legislation. Standardorganization based on separate, consecutive steps - planning, specifications, production and construction - seriously restrict prefabricated timber construction; the requisite timber building expertise is integrated in the planning process at too late a stage and the knowledge needed for detail planning is lacking. A timber contruction specialist is often indispensable for complex multi-storey timber buildings. It would be advantageous to work from the start on a construction project in a production-oriented way with a team of architects, engineers and timber construction planners. This is where the international research project leanWood begins, with the following objectives:
• Optimizing organizational and process models for prefabricated timber construction
• Developing innovative procurement and cooperation models based on existing national legal frameworks
• Clarifying interfaces and responsibilities between the experts involved in the planning process.
• Identifying resources for competence in wood construction and integrating these in the planning process.
The international research team consisted of Finnish, French, Swiss and German universities and institutes as well as the respective practitioners from planning and production.
After exchanging knowledge, the individual countries drew their own conclusions based on their particular national situations and reached results with a national stamp.
Planning process suited to timber construction
In terms of planning prefabrication and timber's properties as a building material are the main differences to conventional massive construction.
Prefabrication requires close examination of the construction process at an earlier stage. Building component and assembly procedures must be taken into account, as they impact design, construction and choice of material. Any alterations made during the course of planning affect deadlines, quality and costs. The complexity of timber construction means that all components must always be viewed together with all layers: above all protection of internal elements from fire and noise, as well as protection against moisture and heat in the envelope, are almost always provided jointly by the shell and the fit-out. Consequently, all the layers must be conceived together. Conventional, step-by-step planning of shell, facade and fit-out simply does not work in timber construction.
Unlike the countries of the other research participants, in the German-speaking world procurement directives have established the separation of planning and execution, which guarantees independence from economic interests. In a series of phases - preliminary design, design and execution planning - a team of separately commissioned architects and specialist planners produces planning that becomes increasingly concrete and can be implemented by the firms. The task of the individual company is then confined to organising and later implementing these requirements in planning their production and assembly work. According to Hoai 2013 the initial architect-contractor contact takes place after the seventh of the nine phases of the planner's services. By this stage the architect has already delivered 66 % of his work.
If expertise in wood construction is lacking at the early design stage, a "re-design" phase is often required after awarding the contract. A further complication is that timber construction companies often have specific characteristics such as production method, level of experience, planning competence and the supply network that can influence the construction. A certain standardization in wood construction, as in the Austrian building component platform dataholz.at, would help reduce such restrictions and lead towards a neutral planning. Within the context of separation of planning and execution, there are two possible strategies for organizing the planning process to better suit timber construction.
In the first the planning team brings with it the necessary competence - through the consultancy of a timber construction firm or an independent expert, e.g. a timber construction engineer, as is done in Switzerland, where this profession has been established for years. The role of the timber construction engineer differs, depending on the competence of the others involved in the planning. As a rule he or she deals with the structural design and the specifications, works on the detailing and is often also trained to carry out the plant and assembly planning for the construction firm. The engineer may also offers planning services for fire protection and building physics. The remuneration depends on the services that the engineer is actually commissioned to provide.
In the second case competence is ensured by awarding the contract for timber construction services at an earlier stage. In the public sector this is only possible in exceptional cases and is described in the section "Awarding Contracts for Services".
Clarifying of interfaces in planning and execution
Architects and planners should always provide their services in harmony with the project phases and in good time. Unclear allocation of responsbilities often leads to gaps in planning and misunderstandings, particularly at the interface between timber construction, fire protection and building technology.
Currently, the areas of responsibility of architect, structural engineer, technical services and fire protection planners are often not precisely defined. Methods developed within the framework of leanWood allow planning processes to be visualized and responsibilities to be clearly allocated. In addition to determining timber-specific plan contents and defining the level of detail (LOD), the responsibilities of the individual actors have been formulated and will be available as an Excel checklist and a web-based application. A matrix offering a detailed description of the component hierarchy facilitates cooperation between architects, structuralengineers and specialist planners in timber construction projects.
Awarding contracts for planning services
In awarding planning contracts public authorities must comply with procurement law, which in recent years has become increasingly complex. The development on the basis of European law and the application to national law has focussed largely on the demands of conventional construction, without considering the different design types, construction and planning processes involved in prefabricated timber building.
leanWood describes the implementation of a prefabricated timber building on the basis of current public procurement law. A negotiation procedure preceded by an (architectural) competition was chosen, as (among other advantages) this system ensures better architectural quality.
The description is accompanied by an example of how a competition is organised. The measures required to prepare the project and describe the various tasks are explained and the creation of an interdisciplinary planning team is outlined. Important aspects include integrating timber construction expertise and interdisciplinary know-how, not only in the planning team, but also in the preliminary phase and in forming the jury. The aim of the model is to assist authorities responsible for public procurement procedures in implementing a prefabricated timber building. Here it is essential that the client should have a basic understanding of the specific requirements of prefabricated timber construction.
Prefabricated building requires adaptations of services as formulated in the specifications. In the Hoai (German Fee Structure for Architects and Engineers), these are based on the principles of conventional construction, which envisages in-depth, detailed planning only at Stage 5 and, partly, in accordance with the progress of the construction work. In contrast, prefabricated timber building requires detailed plans by the end of the design phase. However, Hoai does allow a response to planning procedures specific to timber building. In leanWood, the descriptions of the services provided by all planners (based on the existing hoai) were formulated so as to ensure the necessary level of detail in good time.
The individual descriptions of services, in particular the percentage allocation of basic services among the planning team, are specific to each project and should be examined when the contract is awarded and agreed upon contractually.
Awarding contracts for construction-related services
There are two ways to award construction services: the service description with specifications, which, as well as a general description of the building also includes detailed descriptions of individual services, or service specifications with a performance program, often called a functional specification. With this form of specification tenders are submitted on the basis of a detailed description of the building. This system entails certain risks: often construction work is optimised in economic terms at the expense of design and construction quality, or interfaces and responsibilities may not be precisely clarified. However, if the timber construction firm is involved at an early stage this method can make sense for less complex buildings. A further advantage is that it allows bidders to offer solutions optimised for their particular company.
Unlike private clients, public authorities must abide by public procurement regulations. Function-based specifications are permitted only under certain conditions. In prefabricated timber construction there is an undeniable need to deviate from conventional methods: in addition to the growth of knowledge on the bidder's side and the existence of numerous technical solutions, transferring parts of the (works) planning to the contractor can also make sense. On the basis of a specification system, leanWood describes what is needed to ensure that functional specifications work.
In choosing a building firm the themes of assessing and awarding are often neglected. According to the German Public Procurement Ordinance, the contract be awarded to the most economical rather than the lowest bidder. With prefabricated timber construction, the quality assessment criteria applied to the implementing company are of particular importance. The advantages of prefabricated construction can only be exploited fully if all processes, from workshop planning to prefabrication to assembly, are implemented in an optimal way. leanWood here provides a criteria matrix for weighting price and quality of execution: topics such as providing the quality required by the specifications or executing the work on time are already familiar. For prefabricated timber building several other aspects such as the quality of workshop planning, the experience of the technical office, the building component concept, the logistics concept, phasing delivery of modules, and the assembly concept are also important.
Public authorities are required by law to award contracts in separate specialist or part lots. Reasons for not complying with this requirement must be stated in the contract report. In modern timber construction it makes sense to combine the trades "construction-related carpentry work" and "building envelope (facades, windows and temporary roof)". Issues such as responsibility and liability make combining the specialist trades that produce the "weatherproof shell" unavoidable. The technical reasons for combining contract units lie in prefabrication.
Awarding planning and execution contracts - alternative cooperation models
The leanWood interviews and discussions showed that traditional contract award and cooperation models do not always adequately support interdisciplinary and cross-sector cooperation.
The research project examines different contract award and cooperation models, some of which can be applied in the area of public procurement, some only by private clients. It looks at the extent to which these models provide a legally secured area for trust, reliability and a sense of mutual responsibility among cooperating teams of planners and executing firms.
For example: what is called the building team model can offer private clients an alternative. This model means equal collaboration between client, architect, specialist planners and executing firms at a very early stage. An approach based on partnership contributes to cost and deadline certainty, combined with high execution standards. To optimise the project continuous, monitored dialogue is essential. Here contractual and liability agreements play an important role.
Essentially, public clients can also avail of early cooperation between all actors involved, namely within the framework of what is called "competitive dialogue":
"In the case of competitive dialogue, the client, after publicly inviting an unrestricted number of contractors to submit applications for participation, engages in a dialogue with selected candidates about all aspects of the contract. The aim of this dialogue is to identify the solution or solutions that best meet the client's needs and requirements, on the basis of which the respective applicants are then invited to submit a tender.3 S. 2 GWB)
leanWood examines this process with the help of a scenario appropriate to prefabricated timber construction: to develop optimal solutions with the team of planning and executing companies through competitive dialogue, and to ensure real competitiveness in terms ofdesign and implementation. This represent an opportunity for public clients but the procedure is complex and time-demanding for all involved.
Outlook
To ensure a successful timber construction project it is imperative to find and apply measures suitable for both project and client. For this reason the results of leanWood can be seen as a toolbox that offers tools for different constellations in the planning process and represents a kind of decision-making aid for planners, public and private building clients as well as businesses.
