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Multi-family apartment building Šparna hiža, Koprvnica, Croatia

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Multi-family house Šparna hiža, Koprvnica, Croatia


Project summary

This multi-family apartment building in Croatia was planned and constructed to meet the requirements for a Class A energy performance with less than 15 kWh/m².year for heating. It is comprised of 28 apartments distributed between three floors. The walls have been insulated with 20 cm thick stone wool, the roof with 30 cm extruded polystyrene (XPS). The windows are triple-glazed. Heating and cooling are provided by an underfloor system connected to a reversible heat pump and a gas boiler. A ventilation system with a high recuperation factor ensures good indoor air quality. The domestic hot water (DHW) is generated by solar thermal collectors used in combination with the gas boiler. The total final energy includes heating, hot water, cooling, ventilation and lighting and amounts to 66 kWh/m².year, which is 78% lower than the national building energy performance requirements. Twenty two percent (22%) of the final energy is provided by the solar thermal collectors. The most impressive result of the project is that the building was constructed without having any superior cost difference when compared to that of a regular building which fulfils national requirements. The total costs amounted to 912 €/m².


Construction costs

Costs of land, design, management and construction amounted to 11,485,000.00 HRK (~ 1,500,000.00 €) for 1,644.00 m² (28 apartments). There were no additional costs for the A⁺ energy class type of building compared to a standard quality building.


Building size

1,539 m² net usable floor area (28 apartments, basement, ground floor and three floors with a ground area of 612 m²) which can be recalculated to 912 €/m².


Building envelope

The structural walls are made of reinforced concrete, 20 cm thick, or of brick masonry block, 25 cm thick. The building envelope is thermally insulated with stone wool of a 20 cm thickness for concrete walls and 15 cm for brick walls. The roof is flat and is made out of 20 cm thick concrete and is thermally insulated with 30 cm XPS. The Polyvinyl chloride (PVC) windows are made with triple low e-coated glazing filled with argon, mounted according to RAL installation. (RAL is a German quality assurance association of windows and front door producers, which publish guidelines for correct window installations).

Building envelope U-values:

  • Wall: 0.19 W/m².K (concrete wall) – 0.22 W/m².K (brick wall); allowed Umax = 0.45 W/m².K
  • Window: 0.99 W/m².K; allowed Umax = 1.80 W/m².K
  • Roof/ceiling to the attic: 0.10 W/m².K; allowed Umax = 0.30 W/m².K
  • Cellar ceiling: 0.21 W/m².K; allowed Umax = 0.50 W/m².K
  • Ground slab: 0.13 W/m².K; allowed Umax = 0.50 W/m².K 


Building service systems

Heating and cooling are provided by an underfloor system using the same pipes for both heating and cooling. Heating is generated by a compact heat pump with a coefficient of performance (COP) = 2.8 (90%) or by boilers using natural gas (10%). Each apartment has its own energy meters. The ventilation system runs constantly to supply 0.5 air changes per hour for the entire volume of the apartment. The waste air heat is taken through a high performance energy recuperation system. Hot water is primarily generated by solar thermal collectors, and, if necessary, complemented by gas boilers.


Renewable energy systems

Solar energy for centralised DHW preparation: solar thermal collectors on the roof of the building, connected to the DHW storage tank with a volume of 4,000 liters. The system is designed to primarily use solar energy for hot water generation, with gas boilers as support.


Building Energy Performance


Final energy use:



Calculation method:

HRN EN ISO 13790/PHPP 2009



Monitored in year:



14.95 kWh/m².year

(~ 10% gas boiler,

90% el. heat pump)


Hot water

29.10 kWh/m².year

(50% solar energy)


15.65 kWh/m².year


  4.17 kWh/m².year


  1.69 kWh/m².year


65.56 kWh/m².year

Electrical appli­ances (household electricity)

21.54 kWh/m².year

Primary energy use:


78.95 kWh/m².year

Primary energy factor: 3

Natural gas

17.65 kWh/m².year

Primary energy factor: 1.1


96.30 kWh/m².year


Renewable energy contribution ratio:

22% (solar thermal energy) of the total final energy

Improvement compared to national requirements:


Compared to:

Maximum heating energy demand allowed for new buildings



  • ManagEnergy award winner, “The bold new face of Koprivnica” (European Commission, EACI, Sustainable energy week 24.-28. June 2013)
  • Recognition for best practice in local government in the energy efficiency category (IN PLUS, Association of Croatian cities)

Author(s) information


Nada Marđetko Škoro (Croatian Ministry of Construction and Physical Planning)


Ivana Banjad Pečur (University of Zagreb, Faculty of Engineering)

Lessons learnt

Positive: This building has reached a higher standard than that prescribed by the national legislation with the aim of improving the quality of life of the residents. This includes incorporating renewable energy and also considering environmental protection and shows that it is possible at an affordable price for the users. Problematic: The project showed insufficient experience of the workforce regarding the application of new technology (e.g. RAL installation of windows), quality of works (e.g., airtightness of the envelope) and a lack of information on how the building service system works under real conditions. The users did not have sufficient awareness and also demonstrated a lack of knowledge of using such systems.

Award labels

Available link languages


The two multifamily buildings 'Šparne hiže', energy class A⁺, are unique in Croatia. Marketing efforts were aimed at informing the public of the advantages of low-energy buildings through public lectures, debates, articles in print media and broadcasts on TV.

Funding description

The City of Koprivnica, the investor of the project, has also spent funds on a public awareness campaign, yet the money spent was relatively modest compared to the media attention that followed the construction and promotion.