The first passive modular kindergarten in Slovenia Sentlovrenc TN

The first passive modular kindergarten in Slovenia

Due to a lack of space in the existing kindergarten, the municipality of Trebnje decided to build a new kindergarten in the town of Šentlovrenc. To shorten the building phase, the municipality opted for a prefabricated modular construction system. However, upon completion of the construction, the kindergarten was required to meet the standards of a nearly zero-energy building.

Building design

The new kindergarten is designed as a kindergarten for four groups of children with a total net area of 620 m². In addition to the playrooms, the kindergarten also has a central multi-purpose common room, as well as the obligatory changing rooms, toilets, individual learning spaces, storage for toys and other materials, and spaces for the teaching staff. The floor plan also includes the kindergarten’s own kitchen, which is able to prepare approximately 150 meals per day.

The building consists of 29 prefabricated modules, which rest on isolated foundations. It has a gable roof with a steel structure and sheet metal roofing, which is treated on the inside with an anti-condensation coating. The ridge of the roof is running from east to west and the classrooms therefore face south. The kitchen and the engine room above it are located on the far eastern side of the building.

To construct the building, the REM modul PLUS modular construction system was used. REM modul PLUS allows for a high degree of customisation of the floor plan and is also adapted to meet the highest energy standards. It is the most sophisticated modular construction system used by REM to construct public buildings.

How the work was carried out

After REM was selected as the main contractor for the kindergarten in Šentlovrenc within a public call for tenders, the contract was signed in November 2018 and the planning of the building began. Our team of engineers carefully designed the modules in December 2018 and January 2019, allowing for the manufacturing process to be started in February. All the modules were manufactured by the end of March and the on-site assembly of the building started on 8 April 2019. All 29 modules were placed on the building site in just four days. The roof of the building was completed within eight days from the start of the installation process. This was followed by the final construction works, which included the installation of doors and windows, erection of partition walls, laying of the flooring, construction of the external wall insulation facade, and final finishing of the visible materials. At the same time, electrical, HVAC and water supply works were carried out. This was followed by the “blower-door” airtightness test and the technical handover of the building.

Challenge: Airtightness and sound insulation

The biggest challenge in setting up a nearly zero-energy modular building was to ensure that the building envelope is airtight.

The modular building is made up of several individual modules, meaning that there is a large number of joints. Due to this, particular care was taken when sealing the joints between the modules to prevent uncontrolled and unintentional leakage of warm air through gaps and cracks in the building envelope. The blower door test showed less than 0.6 exchanges of the building’s total air volume per hour (ACH) at a pressure difference of 50 Pa, a condition for obtaining the subsidy by Eko sklad (Slovenian Environmental Public Fund).

For buildings used for educational purposes and scientific research, the requirements for noise transmittance between the rooms are high. It was therefore necessary to design partition walls with such composition that prevents the formation of sound bridges. To meet the requirements, the design of the partition walls was tested by the Laboratory for Thermal Protection and Acoustics at the Slovenian National Building and Civil Engineering Institute before the actual production. The tests provided the necessary information on sound insulation performance of wall assemblies, which were then installed into the building itself.

Energy efficiency

The building is designed to be nearly zero-energy with a heating energy efficiency (Qh) of less than 6 kWh/m³a. As part of the documentation, the “PHPP” calculation was carried out using the method prescribed for passive buildings. The building envelope is additionally improved with the external wall facade featuring stone wool insulation and a finishing layer. In total, the mineral wool insulation of the external wall is therefore 30 cm thick, resulting in thermal transmittance of 0.12 W/m²K for the entire wall envelope. Polyurethane insulation was injected in between the floor profile joists in a 15 cm thick layer. In addition, a 5 cm layer of extruded polystyrene insulation was laid to prevent the transmission of impact sound. The calculated thermal transmittance is 0.13 W/m²K for the floor and 0.11 W/m²K for the ceiling. The building is fitted with wooden windows with triple glazing and doors according to the RAL installation system. The shading system features slat blinds and electric motor control.     

The kindergarten is heated by two heat exchanger pumps via a central heating system, and the same goes for the cooling system. The engine room is located in an unused part of the attic, which also houses the hot water central system and tanks. Mechanical ventilation with heat recovery is installed in all rooms to be occupied. The finished building met all the standards set by the client who also worked with other external contractors to provide all the necessary interior fittings and landscaping.

We have obtained the individual solutions and details required for the construction of the nearly zero-energy buildings and specifically for the design of this kindergarten within the framework of the FlexModNZEB development project under the EUREKA initiative, which was co-funded by the Republic of Slovenia and the European Union through the European Regional Development Fund. We applied for the tender together with the Italian company Piva Group S.p.A., one of the leading manufacturers of windows, doors, walls and ceiling insulation systems. The project was carried out in the period from February 2018 to January 2020. Financial support amounted to EUR 222,250.00. The main objective of the project was to develop a prototype combining five key features: modularity, pre-fabrication, construction flexibility, high energy efficiency and integration of smart installations. We believe that with all five core features combined in an innovative common concept, we have caught up with other prefabricated and conventional construction systems.

Two key project objectives were

  • to ensure that 50 % of the volume of all materials used in the final product were made of wood and wood-based materials;
  • and to develop airtight joints between the modules.


The first objective was achieved by replacing steel floor joists with timber I-joists, injecting wood fibres and using timber in the framing of the external walls and ceilings. According to the final calculations, we have exceeded the first target by more than 20 %, as the share of the wood installed exceeded 70 %.

To achieve the second objective, we carried out two measures. In collaboration with Trelleborg, we have developed a dedicated sealing system to ensure airtight joints between the modules for which the patent application has been filled. Secondly, a service plane was set up along the inner perimeter of the structure. Together, these two measures ensured airtightness of the modular construction system.

Together with the project partner PIVA Group S.p.A., a passive window for modular systems has been developed within the scope of the project. The window’s suitability has been attested by the German Passive House Institute certification.