## 2 Literature Review
In both ways, LSF structures as well as any other NZEBs or passive houses should have airtight building envelopes in order to reduce the ventilation heat losses, reduce the risk of condensation, ensure indoor air quality, eliminate drafts and improve comfort, improve noise insulation of building components, and retain efficiency of the ventilation system. On the other hand, a breathable but wind-tight layer located on the wall exterior should be installed to reduce the impact of wind on the performance of the insulation layer. Both airtightness and wind-tightness require attention and must be optimised in the design stage. Furthermore, being lightweight and thinner than conventional building envelope elements, LSF structures have lower thermal inertia, thus reducing the possibility of passive energy storage in the building envelope and decreasing the overheating problems in buildings with high internal gains, or, on the other hand, increasing the summer overheating risk, especially in southern European climates [29]. Despite generally resulting in a more versatile indoor thermal environment in case of LSF, the analysis in [29] showed that lower thermal inertia of LSFs may have benefits considering the intermittent occupancy of the building. Regarding the load-bearing properties, the main disadvantage of this system is that individual profiles are usually unable to transfer loads independently, so two or more profiles must be connected to each other, and only then do they form a load-bearing panel. Therefore, the performance is more sensitive to imperfections related to dimensions, and in terms of budget, proving sufficient resistance is much more complex [21]. LSF structures can be classified into three types [23; 30], depending on the position of the thermal insulation: (a) cold frame construction; (b) warm frame construction; (c) hybrid frame construction (Figure 1). In conclusion, each type of LSF structure has their advantages and drawbacks. The common drawback would be the difficulty to achieve airtight layer, keeping in mind that one needs to run installations (electrical, water, sewage, and possibly heating, cooling, ventilation, etc.) through the structure. The other deficiency of the LSFs shown in Figure 1 would be free moving air, which would increase heat losses due to convection within the LSF structure. In order to avoid the issues of inadequate airtightness and freely moving air, this paper proposes the further development of existing LSF typology (Figure 2) by introducing the installation layer from the inside with two-fold function: (i) to enable continuity of airtight membrane with minimal penetrations, and (ii) easier access to installations. Moreover, by filling the entire thickness of the structure with thermal insulation, one avoids convection due to free air circulating (Figure 2). Figure 1: Classification of LSF structures: (**a**) cold frame construction; (**b**) warm frame construction; (**c**) hybrid frame construction. This newly proposed LSF structure is considered to have significantly improved thermal behaviour compared to conventional LSF structures; however, extensive calculations should be performed in order to evaluate its performance. Therefore, the influence of thermal bridges on the thermal behaviour of the building envelope elements, but also on the energy consumption of the entire building, is investigated using the example of a single module with a useful floor area of less than 50 m\({}^{2}\). This paper presents the study of 2D thermal bridges, in which proposed LSF walls (Figure 2) meet other building elements, such as a corner between two walls or a junction with the floor, roof, and a window. Secondly, the research is focused on whether the proposed LSF design approach can reach the NZEB levels as prescribed in the Croatian legislation [14] and simultaneously fulfil the EU targets.