Life cycle costs and environmental performance assessment for a NZEB

One of the first tasks within AZEB project has been the analysis of life cycle economic and environmental performance of existing ‘nearly zero energy buildings’.

This detailed analysis will be discussed through stakeholder collaborative workshops, and will serve to discuss how  the solution adopted, if any other solutions would be nowadays available, and barriers and potential improvements through the building process.

The building studied is in the neighborhood of Salburua, city of Vitoria-Gasteiz, in the Basque Country, North of Spain.

  • Location-  Salburua, Vitoria-Gasteiz
  • Building type – Apartment block
  • Number of dwellings – 176
  • Gross floor area – 15,079 m2
  • Heated floor area – 12,417 m2
  • Garages – 184
  • Storage spaces – 176

Affordable Zero Energy Buildings


The building façades are composed of precast concrete panels with internal plasterboard and high levels of insulation, reaching a transmittance value of 0.35 W / m2K. Particular attention has been paid to the correct insulation in the edges of the slabs in the encounter with the concrete panels and to the joints of exterior carpentry with facade in order to minimize the thermal bridges. The exterior carpentries are aluminum with frames whose transmittance is 1.9 W / m2K.

The frame and glass assembly has a transmittance for the hollow of 1.5 W / m2K. In the case of the cover, the transmittance is lower than 0.24 W / m2K, all these values being below the normative requirements in force at that time. In order to ensure good indoor air quality and user comfort, a double-flow controlled mechanical ventilation system with heat recovery and regulation modules at the inlets and outlets (damp rooms) of the air has been installed, allowing a greater energy savings. Likewise, potential energy losses due to air infiltration have been taken care of, paying special attention to the main leakage points through cracks in the dwellings (floor / wall joints with walls, joints of doors and windows and steps of installations) and seals have been made to reduce such infiltrations.

The energy installations are made up of two high performance natural gas boilers and 240 kW each, complemented by cogeneration engines with an electric power of 5.5 kW and a thermal power of 12.5 kW each. The building also includes a photovoltaic installation with a power of 59 kW, which covers 430 m2 on the south facade.


According to the monitoring data, the cogeneration is currently not in use and the photovoltaic installation delivers its whole electricity production to the grid.
In order to evaluate the economic and environmental performance of A32, a life cycle analysis (LCA), and a life cycle cost analysis (LCCA) have been carried out. The standard EN 16627: 2015 Sustainability Of Construction Works – Assessment Of Economic Performance Of Buildings – Calculation Methods and the standard EN 15978:2011 Sustainability of construction works. Assessment of environmental performance of buildings. Calculation method, describe the main steps for assessment of environmental and economic performance of buildings through its life cycle, and have been used for this study.
The calculation performed considers a 50-year service life for the building, and the life cycle phases included are the product manufacture and construction of the building, and its use and operation.

Two initial conclusions

Overall, LCA environmental results show that environmental impacts for ‘nearly zero energy buildings’ are dominated by the product manufacture and building construction, which are the major contributors to the environmental impact throughout the life cycle.  This is a significant difference with ‘conventional’ or old buildings, where the operational stage with associated large energy use has very large environmental impacts, much larger than the construction phase.  Two initial conclusions from this environmental analysis are a) that minimizing operational energy use is a first priority, and b) that once that energy use is ‘nearly zero’, attention should be focused in environmental impact associated to building materials and products.

Construction phase 70% total cost

As far as economic analysis is concerned, the construction phase of the building is responsible for more than 70% of the total cost of the building during its lifetime (50 years), followed by the operation phase, where energy expenditure represents about 17% total life cycle costs.  This is also substantially different to ‘conventional’ buildings, where operational costs through building life cycle can be comparable to initial costs of the building.

Economic payback

It is important to highlight the particularly large importance of the initial investment in nearly zero energy buildings. The initial additional investment costs of about 3% represent a benefit for the occupants of about 67% of their operational costs. And analyzing life cycle cost of these investment (regardless of who invests and who pays the energy bills), the economic payback is of about 6 years.

Building energy efficient at a cost similar to social housing possible

The figure below shows the share of GHG emissions and costs per each life-cycle stage for the building.

case study life cycle costs

If we focus on the investments made, it is interesting to note in this regard that the additional investment in facilities (0.43%) and energy improvements of the building (2.51%), which amount to 2.94% of the initial investment, have an impact on energy savings for the user of 67%. Compared with a traditional building, the economic return of the additional investment would be 6 years, and more important, it impacts on the end user, in this case, the occupants of social housing. The data show, therefore, that it is possible to build energy efficient homes (meeting the European requirements for 2020) at a cost similar to the social housing currently promoted by Visesa and achieving savings of close to 70% for future users.