This article is based on a paper published in Protocol Volume No. 55 of the Research Group for Cost-effective Passive Houses with the title “Multi-storey social housing: Cost-effective and energy efficient – (not) mutually exclusive?”. The original article by Esther Gollwitzer is available in German and can be accessed here.

The topic of energy efficient construction is often accompanied by the question of costs. What do these depend on, and how can they be kept low? This article will point out various dependences and also possibilities for influencing these. It will deal only with construction costs, independent of any later savings through reduced energy costs. These will be discussed in the next article in this Protocol Volume.

In recent years, construction costs have continued to rise in Germany. Figure 1 shows the progression of construction costs and the dates of the energy ordinances (Thermal Insulation Ordinance, EnEV). One would expect that the more stringent statutory requirements for the energy standard would be reflected in an increase in the construction costs at the respective times. However, this is clearly not the case; instead a correlation can be seen between the increasing number of new builds and rising construction costs.

Fig. 1: Progression of construction costs (€/m²) compared with the number of newly built residential units; more stringent regulatory provisions are indicated as blue points. Source: Schulze Darup 2019

Construction costs consist of different parts and are influenced by many different criteria and boundary conditions: configuration, statics, fire safety, energy efficiency, function, design, urban development etc. There are several ways to filter out the actual cost share for energy efficiency:

• by comparing different implemented projects by comparing two buildings which differ only with regard to the energy standard
• by comparing the costs for an implemented building with the calculated costs for a variant implemented with a different energy standard
• by comparing different calculated costs

Below we will present various studies which deal with the construction costs for different energy standards.

In this study relating to rented housing construction in Hamburg [Leutner 2016], new builds (2011 – 2014) for which the costs had been billed were compared: subsidised rented housing, 117 projects with 4,780 residential units, cost group 300 – 700. Figure 2 shows the costs sorted according to the energy standard. With each energy standard there is diversification of low-cost and expensive projects; however, the average values of the energy standards from EnEV to Passive House are at the same cost level. The differences are negligible.

Fig. 2: Charged costs for multi-storey buildings in Hamburg do not show any differences between the different energy standards; source: [Leutner 2016].

In these studies from Austria [Ploss 2017] [Ploss 2019], which have been presented in more detail in a separate article in this Protocol Volume, various quotations were obtained for a project and the costs for a large number of design variants were determined in this way. These are shown in the cluster of points in Figure 3. Here it can clearly be seen that with an identical primary energy demand in each case the costs differ by around 200 €/m² depending on the design, but with a different primary energy demand the fluctuation margin is only around 100 €/m². This shows that extra costs for more efficient buildings are lower than cost differences which arise as a result of other decisions.

Fig. 3: 30,000 variant: quoted net costs for construction (KG 1-9 ÖNORM) presented as a function of the primary energy demand (PEB) based on OIB 2011; source: [Ploss 2017]

In studies relating to building renovations for Hoheloogstrasse and Schlesierstrasse in Ludwigshafen, the renovation costs were analysed [Kaufmann 2010]. These were two retrofitting projects using Passive House components (2006 – 2008), with 12 and 15 residential units respectively. For the first project, additional costs of approximately 175 €/m²living area were determined for retrofitting with Passive House components in comparison with a low energy building variant (uncertainty ± 20 €/m²). Although the prices for insulation materials had increased by the time of the second project, this project could be implemented at a cost that was lower by 27 €/m²living area due to reduced prices for windows and planning experience. In retrospect, another potential for further optimising the costs was recognised: in subsequent projects the perimeter insulation could be implemented differently and therefore more cost-effectively. The report also shows how the costs are spread across individual disciplines and building components.

An exact analysis of the composition of costs would be interesting. Unfortunately, except for the building renovation mentioned above, very little has been published regarding the breakdown of costs. However, two studies have performed interesting evaluations relating to the influencing variables. The first is the above-mentioned study from Hamburg with a large number of projects and the other is a study from Austria [Treberspurg 2009] with 24 projects (newly built housing complexes 2003 – 2008, 1500 apartments, construction costs (CG 1 – 9)). The absolute costs in the two studies differ as follows: the Austrian study refers to projects from the years 2003 – 2008 and shows the costs CG 1 – 9 (ÖIB - Austrian Institute of Construction Engineering). The Hamburg study relates to projects from the years 2011 – 2014 with cost groups 300 – 700, so in contrast to the Austrian/Vienna study, development costs and reserves are not included in this.

Both studies show that there is a correlation between the building size and costs. Larger buildings tend to be built at lower prices. Even if the statistical evaluation of the Hamburg study only yields a weak correlation, it is still systematic, i.e. reproducible, because the probability of error is very small with 3 %.

Fig. 4: Austrian study: costs (CG 1 – 9) in relation to living area; source : Treberspurg 2009

Fig. 5: Study from Hamburg: costs in relation to living area: there is a weak, but systematic correlation (probability of error: 3 %); cost group 300 – 700; source: Leutner 2016

However, the studies differ with regard to the influence of compactness of the buildings. The Hamburg study comes to the conclusion that there is no statistically significant correlation between compactness and costs. In contrast, the Vienna study (without exact statistical evaluation) shows that a good level of compactness has a positive effect on the costs. It is hardly conceivable that compactness would not have an effect; costs can certainly be saved with compactness if all other costs remain the same.

Fig. 6: Study from Vienna: costs (CG 1 – 9) in relation to the SA/V ratio; source: [Treberspurg 2009].

Fig. 7: Study from Hamburg: costs in relation to the SA/V ratio: no statistically significant correlation; cost group 300 – 700; source [Leutner 2016].

Both studies show that there is no correlation between the energy demand (i.e. level of efficiency) and the costs. Of course, thicker insulation costs more than thinner insulation, but this small difference is overlaid by other cost influences (e.g. selected material, design, features etc.). In addition, investment costs relating to technical systems can be saved with good Passive House planning.

Fig. 8: Study from Vienna: costs (size of circles) in dependence on the primary energy demand and SA/V ratio; costs CG KG 1 – 9; source: [Treberspurg 2009].

From the construction of the first Passive House in Darmstadt in 1990/1991 until today, a clear learning curve can be observed with regard to the costs, meaning that additional investments for a higher level of energy efficiency have decreased. Besides this overall learning curve in energy efficient planning and also in product development, a personal learning curve is of decisive importance. From project to project, every Passive House designer saves more planning time and investment costs. For this reason, it would be of great advantage for housing construction companies to have their own planning departments which can develop their own solutions for different areas in the interest of cost-efficiency. This can not only reduce costs and the energy demand but also user satisfaction and durability can be increased.

Studies on low-cost residential building construction [Potyka 2007] by Hugo Potyka point out 150 suggestions for saving costs. These were worked out in 1996 and in 2007 were again discussed, reassessed and amended. The following key statements can be made about specific suggestions which can be reviewed [Potyka 2007, pages 1 – 4]:

• “Cost reduction … more likely to be achieved only through an amount of smaller savings”
• “Every little bit counts”
• “No construction method has been found which is always the most cost-effective everywhere”
• “However, Stamm-Teske, a Swiss architect with experience gained in Austria and the Netherlands as well, is of the opinion that the existence of regulations not (only) prevents construction of low-cost housing, but also their acceptance.”

Apart from this, the study offers a little perspective on the construction method in the Netherlands which in 2007 was 40 – 50 % more cost-efficient than in Germany. The reasons lie in simpler development standards and also in rationalisation. The statement regarding prefabricated elements is interesting: these are cheaper only if the design is already geared to this, if contractors have experience with prefabricated elements and if this concerns large projects.

The report by [Schulze Darup 2019] is the latest of these studies. Besides background information, it also presents variants and gives planning tips in great detail. There are separate sections on various disciplines and building assemblies, and at the end of each section a table with precise information is provided. This can be used as a checklist by building owners and designers already in the early design phase. Besides many cost comparisons for individual building assemblies (see Figure 10), the report shows the differences in costs from the KfW 55 standard up to the Passive House standard together with their large fluctuation margin, always presented in comparison with an EnEV building. Different variants are shown for the Passive House energy standard. Thus, one square metre of a high quality exterior wall for a Passive House may mean an additional cost of €10 to €26. With the optimised Passive House variant, this difference is reduced to an additional cost of €5 to €10 in contrast with an EnEV building.

Fig. 10: Exterior walls: additional cost range in comparison with an EnEV building; source: [Schulze Darup 2019].

Fig. 11: Additional or reduced costs for Passive House buildings compared to EnEV 2016 are shown with their fluctuation margins. (Diagram prepared using data from [Schulze Darup 2019]).

The design of a building has a big influence on the overall costs. The possibility of influencing construction costs is greatest in the early planning phase. That is why it is important to pay attention to the costs already in the design phase. Housing developers can steer this by stipulating e.g. the size of rooms, balconies instead of loggias, parapet windows instead of floor-to-ceiling windows, and the type of building structure. They should review the preliminary design also from the cost point of view (e.g. SA/V ratio, standard dimensions, space efficiency of the floor plan design). Checklists, evaluation systems and designPH (see below) can serve as tools. Finally, enough time should be planned for optimisation of the design.

Unfortunately, the opportunity to influence the costs with the design is often missed. Since precisely housing developers repeatedly go through this process, it is worth investing money and time in this design phase. The effort for it is small in comparison to the saved construction costs. This has been demonstrated by the experiences of housing developers who have prepared their own assessment systems for this purpose.

DesignPH is a plug-in for SketchUp which enables the graphic input of building data. An energy balance is immediately calculated in this program, which allows designPH to compare different designs with one another. The associated heating demand of each design is displayed for an identical quality of building assemblies. As a result, an overall assessment of the compactness, orientation, windows sizes and shading is obtained. The KliNaWo project has made use of this advantage. After the first sketch, cost optimisation was carried out using designPH. The differences in the design of the new variant and the original design are not very noticeable (see Figure 12): with the same heating demand of 15 kWh/(m²a), the costs could be reduced by 50 – 75 €/m² living area through optimisation of the design. The influences on the construction costs become apparent here.

Fig. 12: KliNaWo: Model with designPH: on the left is the initial sketch, on the right is the variant optimised for cost and energy; source: PHI

The PopUpDorms student hostel is a successful example of a cost-optimised residential building. It is a Passive House construction that was built in 2015 at a cost of 1140 €/m², which is far less than the usual construction costs in Austria. In this way, 40 students can live here for a “warm rent” (basic rent plus heating) price of €350 each and can enjoy Passive House comfort at the same time. It was built without any housing subsidy. The building consists of a timber frame construction without chemical wood preservatives which can be assembled and disassembled four times, and can thus change its location as needed [Lang 2015].

Fig. 13: PopUpDorms: mobile student hostel as a Passive House construction for 1140 €/m²; picture: LANG consulting.

In summary, it can be said that it is not easy to filter out the actual additional costs for energy efficient construction because these are always interdependent on other planning decisions (e.g. type of façade, interior finishing, window area, design etc.) and are overlaid by their fluctuation margins. The difference in costs between the Passive House standard and poorer energy standards is substantially lower than frequently discussed. In part, the total costs of buildings with different energy standards do not differ at all. This is because the small cost differences in terms of energy efficiency (more insulation naturally costs more) disappears in a much wider range of other costs for the relevant elements (e.g. floor coverings, bathroom facilities, design). In addition, the better level of energy efficiency of a building offers more comfort for users and more protection from structural damage and price increases. The economic advantages of long-term energy cost savings with Passive House buildings have been presented in detail in Protocol Volume No. 42 of the Research Group for Cost-effective Passive Houses [AkkP 42] and have also been confirmed by current experiences with implemented projects.

Whether the objective of cost-effective residential buildings is achieved is determined by the question of whether the opportunity is taken to influence costs by means of the design. Cost optimisation and energy-related optimisation often go hand in hand (e.g. there are no costly head starts and setbacks???) z. B. keine aufwändigen Vor- und Rücksprünge). Implemented projects demonstrate the success of this approach. Housing development associations have the advantage that they are able to use their personal or entrepreneurial learning curve relating to the Passive House construction method for many other projects.

[Schulze Darup 2019] B. Schulze Darup: Kostengünstiger und zukunftsfähiger Geschosswohnungsbau im Quartier (Cost-effective and future-oriented multi-storey residential buildings in districts); Berlin 2019

[Leutner 2016] Leutner, B. et al.: Analyse des Einflusses des energetischen Standards auf die Baukosten im öffentlich geförderten Wohnungsbau in Hamburg (Analysis of the influence of the energy standard on construction costs in publicly subsidised housing construction in Hamburg); Forschung + Beratung für Wohnen Immobilien und Umwelt GmbH; Hamburg, 2016

[Ploss 2017] Ploss, M. et al.: Model project KliNaWo, Klimagerechter Nachhaltiger Wohnbau (“KliNaWo” climate-compatible sustainable housing construction), Interim Report 2017

[Ploss 2019] Ploss, M. et al.: Model project KliNaWo, Klimagerechter Nachhaltiger Wohnbau (“KliNaWo” climate-compatible sustainable housing construction), Monitoring Report), July 2019 – short version

[Treberspurg 2009] Treberspurg, M., Smutny, R. et al.: Nachhaltigkeits-Monitoring Ausgewählter Passivhaus–Wohnanlagen in Wien (Projekt NaMAP) (Monitoring sustainability of selected Passive House residential complexes in Vienna, NaMAP Project), Final Report, University of Natural Resources and Life Sciences (BOKU) 2009

[Potyka 2007] Potyka, H.: Kostengünstiger Wohnungsbau (Cost-effective housing construction), ÖIAV 2007

[Kaufmann 2010] Kaufmann, B.; Ebel, W.; Feist, W.: Ökonomische Evaluierung zweier Sanierungsprojekte mit Dokumentation der abgerechneten Kosten: Hoheloogstraße und Schlesierstraße in Ludwigshafen, Abschlussbericht zum Projekt im Rahmen IEA Task 37 (Economic evaluation of two building renovation projects with documentation of charged costs: Hoheloogstrasse and Schlesierstrasse in Ludwigshafen, final report on the project in the context of IEA Task 37), funded by the Federal Ministry of Economics and Technology BMWi, represented by the project sponsor BEO Forschungszentrum Jülich GmbH, 2010

[Lang 2015] Lang, G.: Press release – PopUp Dorms – GreenFlexStudios – Economical Passive House for Students in Record Time, Vienna/Schwanenstadt 2015

[AkkP 42] Research Group for Cost-effective Passive Houses Protocol Volume No. 42: Economic evaluation of energy efficiency measures, Passive House Institute, Darmstadt 2013

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PB 55: Multi-storey social housing: Cost effective and energy efficient – (not) mutually exclusive?