Swedish Article: Passive House Construction - What is the Difference Compared to Traditional Construction? (Boqvist. et al, 2010)
Introduction
The passive house concept is not only starting to appear on the Swedish market but is becoming a popular construction approach world wide. "The passive house concept is based on the optimisation of all energy relevant components: building elements of the opaque building shell, windows and doors, ventilation, heating, hot water and electricity use" (Passive house institute, 2011).
The question that the article poses is; how will reducing construction costs, which is priority among all competitive developers in Sweden, affect traditional housing construction methods which are integrated into the Passive House approach, while still trying to achieve low energy houses at a realistic cost.
The paper examines how traditional construction activities may be affected, when the end product is aiming at achieving passive standard.
The Traditional & Passive building process
The building phases highlighted in figure 1.1 for the traditional building process in Sweden are similar to passive house concept in their approach, but may vary in time durations, costs etc while being carried out.
Fig 1.1 Building Phases (McCartney. D, 2007)
Conventional Construction in Sweden
The traditional construction phase in Sweden consists of six main stages with associated activities as follows:
- Ground works - excavations, pipe runs, landscaping (continuous process)
- Foundation works - insulated reinforced concrete slab
- Load bearing structural works - concrete or timber frame or steel, prefabricated or developed on site
- Structural completion works - finishing the building envelope, facade, roof, windows, doors etc
- Interior completion - Internal walls and floor
- Installations - external tubing, control systems, etc, most time consuming stage.
With the construction industry aspiring to reduce building costs, waste is one of the main area where savings can be made during the construction phase. A Swedish report (Report not available online) carried out on waste generation in Swedish building projects, estimated 30-35% of the project's construction cost are generated by waste.
Passive house construction and production
A qualitative investigation of how on site construction of a passive house varies from the development of a conventional house, was carried out in the form of in-depth interviews. Six Swedish passive house projects were chosen, along with the six construction managers that overlooked the projects. The reason behind the decision to choose construction managers over other qualified experts e.g. Architects, was due to their better overview of the projects from design/planning stage to construction phase. The Interview questions focused on aspects where problems may arise with passive construction methods through the use of traditional techniques. All results from the interviews were compiled and categorised under the following seven sections which are described below:
1) Systems design: Load bering structures were of the same materials, with thermal bridge minimisation highlighted. The building envelope design was affected, where plastic foil was used as vapour barrier to maximise air tightness, increased workmanship and quality was required.The foundation works were very similar with more emphasis on thermal bridge free design. The external walls had a far greater thickness of insulation, e.g. increased material prices compared to conventional construction. The window bays took more time to construct due to the recessed angle which decreased air tightness achievability. Wooden roof construction was estimated to take eight times as long to conduct due to increased accuracy to achieve air tightness for passive standard.
2) Building documents: Construction managers that witnessed increased detail in documentation, found less problem solving was required. It was established that any project that witnessed stoppage due to energy performance design aspects were delayed for considerable lengths of time.
3 Construction Planning: It was figured that in project where construction managers participated in early stages; many unnecessary problems were bypassed at development stage. A contiuous information feed with increased teamwork proved majorly beneficial.
4) Working Methods: Prefabrication was seen as less accurate in relation to thermal bridge free design.
5) Quality control: Cheek lists for air tightness, thermal bridging and control of moisture in organic material were pivotal to the cause, of achieving passive standard.
6) Leadership: It was figured that the leader must never loose control of construction activities as consequences will be to severe.
7) Attitudes: Project's where more time was spent planning and preparing witnessed increased satisfaction during construction. Quality was considered a higher priority than time.
Conclusion & Critical aspects of paper
The investigation aimed to identify whether, current construction techniques, which are used in the Passive house developments carried out in Sweden, are the most effective, I feel that interviewing construction managers was possibly not the most accurate way of establishing the most effective methods of achieving an energy efficient development. The quality level of previous work carried out by the six interviewees was never investigated. I feel an analysis on specifics would have been more accurate and promotional from a passive house perspective, e.g. carry out tests on air tightness of roof structures between traditional and passive constructions, estimate the potential life cycle savings and offset these savings against the extra labour required or additional material costs.
Cost savings is a major priority in the paper where it is highlighted that the passive house concept, results in excessive charges on the client due to longer working periods, during the interviews it was established that at construction planning stage three prototype projects, the size of a garden sheds was conducted by three different companies, where it was possible for the construction personnel to carry out "practise work", it was stated that this technique saved time and money. How was the time and cost saving calculated, how is it possible to estimate or quantify problems that never arose.
It was stated in the concluding section of the paper that there was "a clear need to find alternative construction methods" to cut construction time and costs, "Prefabrication could become a good substitute". In my opinion I believe this is completely contradicting what one company suggested in relation to working methods [seen above in 4)]. Prefabrication option is shown below.
