Identification of differences between Passive house & Conventional style construction phases

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.

      

Belfast Passive House construction methods and materials used

The GO Passive house is situated in Belfast, Maine, USA; the development is the first certified Passive house in Maine and the twelfth Passive house to be constructed in the entire United States. The dwelling was a model for a 36-home eco-village that began construction in spring 2010. The Geological Prototype home was a design and build collaboration, with the aim of achieving a 1500 sq/ft super energy efficient home that uses 90% less energy compared to conventional buildings. In recent years Ireland's weather patterns are quite similar to those seen in Maine, where winters are very cold with severe frosts occurring and summers providing occasional heat waves, this is why I feel that some of unique details and construction methods used in the GO Passive house to achieve the required thermal performance and also keep the price at affordable levels could potentially work in Ireland.  

The Slab on Grade foundation system was used in the Belfast development, where a compacted gravel base was installed then a sand and concrete flow-able self levelling mixture on top of this base was poured. A layer of high density insulation was then installed running approximately two foot outside the house boundary to hold the heat in during the winter months. This high density insulation is the material upon which the Insulated Concrete Form (ICF) footings bear on, this provides a complete thermal and moisture break between the concrete and the footings to ensure the dwelling will be isolated from the ground. The ICF prefabricated formwork comes in clip together sections which hold the rebar in place. The services/utilities entrance area includes the water line, electric cable, sewer outflow pipe and heat sensing probes to monitor the septic area and under-slab temperatures for the geothermal heating system, this is sufficiently sealed with expanding foam. There are two peeks tubing pipes entering the services inlet, one is buried and run at 5 foot below the ground with the water line for convenience, and the other pipe is inserted in the sewer pipe, as a lot of warm water exits the building into the septic tank, this provides the pre-heat for the heat recovery ventilation system installed.

An 8 inch layer of rigid insulation is placed on the internal surface, with a layer of plastic also added that acts as a vapour barrier and is run up the walls. Once the footings were cast the pressure treated mud sill or wall plate was attached and then a second plate added so the structural insulated panels (SIP) which consist of orientated strand board on both faces with a foam centre, could be easily installed. The SIPs were pre-cut in a factory in Vermont, the 4" wide by 24" long panels slide and lock systems means accuracy, speed of production and speed of construction was achieved which in turn reduced labour costs. The panels were attached, to locally sawn white pine timber frame 6 inch x 6 inch beams which were attached beforehand to the foundation with steel brackets and bolted and plated together, which was all subsequently sealed with caulk to ensure no air leakage. The panels were installed with an intentional vertical void left internally so expanding foam spray and the external surface of the panel connections was primed to remove grit so the insulated tape could be attached sufficiently.                               

The triple glazed tilt-turn windows were imported from Germany; with a pine wood frame and an aluminium clad exterior finish which conducts energy. There is an Argon gas between each layer that provides excellent thermal performance and the insulated glass optimises solar gains with a 60% acceptance ratio and reduces heat loss which has a low e-coating that increases the energy insulation of the windows. The external finish is a board and batten effect and the roof is a metal clad.

"Out of the Blue" Passive house Wicklow

Today we looked at some of the building details and systems used in  the 400sq. ft. passive house "out of the blue" in County Wicklow, the dwelling is a 2-stoery single family detached structure, the first of its kind to be built in Ireland and is owned and occupied by architect Tomas O Leary and his family. The dwelling was designed, specified and supervised through his own company MosArt . The house is officially certified as a passive house by the German Passive House Institute. The external walls are 560mm thick with U-values of 27 W/m2K taken for the BER certificate purposes, the exterior walls consist of  block clad and 315mm  expanded polystyrene insulation supplied by greenspan products ltd.

The windows and doors were a very complex section of the dwelling in both sourcing and installing, Optiwin Ireland was the  chosen company to conduct the procedure as they sourced all the required certified data and calculations from the Optiwin company in Austria. The windows are a triple glass pane cavity 12mm thick filled with Argon, and provides a glass U-value of 0.6 W/m2K and a Frame U-value of 0.73 W/m2K.The Ventilation system installed in out of the blue dwelling is a high end Paul HRV (heat recovery ventilation) unit and was installed by pure renewable energy.

O' Leary first became interested in the Passive house concept at a conference in Co Kerry when a Swedish architect explained how he designed houses without any conventional heating system even in the coolest of climates, many Passive house do not install a heating system at all, but Tomas installed a Calimax pellet stove with a back boiler which heats a small number of rooms and bathrooms through radiators if required. The radiators and stove heated proportions within the house via the pellet stove are exceeding the 30% required by the Deap, so the stove must be entered as the principle heating system.

In Out of the Blue however, there is a Calimax pellet stove with a back boiler supplied by Greenheat. This back boiler heats a small number of rooms/bathrooms with radiators, if required. Quite inadvertently, these few radiators, along with the space heated directly by the stove means the proportion of the house heat-able by the pellet boiler is over the 30% required by Deap, and so the stove can be entered as the principal heating system.

Retrieving the relevant certified, translated, accredited test data for all the different products installed was a very strenuous task, but Tomas persisted with the view of a clean, low energy house for his family’s benefits’, compared to the  conventional terraced house they previously lived in.

First steps

It has occurred in the past that passive house building techniques did not suit specific areas for example Californian passive solar building techniques were directly copied and applied to European passive construction projects, this was a major mistake and should never be repeated due to the fact that insulation, ventilation and window details should be designed and integrated to suit the climate and geographic conditions of differing location from China to California to Central European locations, so the Passive concept can achieve maximum capabilities, while taking the local building traditions and specific climatic conditions into consideration. The mistake leads to poor results from the development due to the difference in solar gains between sunny and cloudy locations.

It must be identified that the laws of physics or general principle will remain identical for all passive houses worldwide be it a warm or cool climate, where levels of efficiency must be achieved when cooling, heating, lighting or other energy demanding elements are in operation. Heating in a cool climate during the peak of the cold season must not exceed 10 W/msq, Passive methods to reduce energy demand include increased insulation, heat recovery via ventilation system, super windows, passive solar gains etc. Peak heating loads should be set at design stage and is easier to achieve internal comfort in warmer climates compared to cold climates where more thought is required at design stage. Cooling is viewed as essential to heating depending on location and can achieve reductions in energy demand in the form of shading, insulation, subsoil heat exchangers and by reducing the internal heat loads with the incorporation of highly efficient appliances.

If affordability in comparison to conventional buildings is achieved, the high level comforts provided by a passive house along with reduced energy use and less associated cost compared to achieving a zero energy building will entice clients towards the passive concept. The high costs associated with ground coupled systems used for heating and cooling need addressing where alternative option may prove more beneficial from the budget provided by the client.

The parametric study of the building design is essential to understand energy demands, financial investment and the level of healthy environment provided, this study will effectively develop passive solutions for varying climates worldwide.

Regards,

Martinkeanepass.

setting up my passive blog.

25-1-11 passive blog up and running.