In order to maintain the quality of construction for nearly zero energy buildings and to reduce the pressure on construction workers with the addition of the need for faster and simpler structures, the use of cavity-insulated LSF (lightweight steel frame) panels is increasing. Requirements for performance quality, quality of life, and low energy consumption have led to the need for closer examination of heat transfer through building elements. Due to the impact on increased heat losses, thermal bridges can cause structural damage due to the increased risk of water vapor condensation on the interior surface. In this paper, numerical heat transfer analysis with the optimization of thermal bridges for LSF cavity insulated walls was made in order to reduce the overall transmission heat losses. The effects of different cavity insulation materials (mineral wool and polyurethane foam) on overall heat transferred through the building elements were analyzed. Additionally, in order to reduce the effect of thermal bridges caused by the steel frame structure, the PVC spacers between the steel and sheathing panels are introduced into calculation models. Lastly, additional layers of insulation were added on the internal and external sides of the LFS panels in order to minimize the effect of thermal bridges and maximize air tightness. Combinations of all three setups were made for wall–window, ceiling–wall, wall–floor joints for the numerical calculation. For each setup, the temperature distribution and overall heat transferred through the building elements were calculated. Different thermal bridge designs have a significant influence on the overall heat transfer, and by choosing the optimal design, the transmission heat losses can be reduced by up to 67%.

This study investigates the influence of mechanically recycled EPS on the mechanical and thermal properties of EPS composites for use in thermal insulation. Composites containing 5%, 10%, 25%, and 50% recycled EPS were produced using two recycled sources (construction EPS and packaging EPS). The tested properties included density, compressive strength at 10% deformation, bending strength, and thermal conductivity. Results show that increasing recycled content leads to a decline in density, with a more pronounced drop at higher recycled levels, particularly above 10% recycled content in the S1–25 series and 25% in the other series. Compressive strength correlates closely with density regardless of recycled content or origin and the behavior largely aligns with EN 13163 predictive models for virgin EPS. Thermal conductivity remains unchanged at lower recycled contents, with minor increases (up to 6%) observed at 50% recycled content. Bending strength decreases with increasing recycled content with greater losses noted in specimens containing packaging EPS. However, despite containing recycled materials, the empirical equations stated in EN 13163:2016 for predicting thermal conductivity and compressive stress at 10% deformation remain closely correlated regardless of recycled material content, indicating that density remains the main parameter for predicting the tested properties. These findings suggest that EPS with moderate recycled content can meet performance expectations, though further research on microstructure is recommended to understand property degradation mechanisms at higher recycled levels.

Despite emphasizing sustainability, the dominant method of waste management in the region is still landfill, rather than recycling. An analysis of previous EPS recycling research reveals inconsistent conclusions regarding the degradation of recycled EPS. One proposed application of recycled EPS is in the production of boards for underfloor heating and cooling. An overview of the minimal requirements for such boards, existing underfloor heating systems, and an analysis of the advantages and disadvantages of technical solutions for pipe installation in the boards are provided. The aim of the article is to highlight the results of previous research, the lack of knowledge, and to encourage further research into EPS recycling and its future applications.

The mechanical performance of expanded polystyrene (EPS) thermal insulation produced with mechanically recycled content has received limited investigation beyond the single point compressive stress at 10% strain (${\mathcal{\sigma }}_{10}$) declared under EN 13163. This study quantifies the cumulative volumetric energy absorption W(ε) and the specific energy absorption SEA(ε) of EPS containing recycled material from two distinct end-of-life sources. Construction waste (S1) and packaging waste (S2) were tested to find whether energy-based metrics reveal source effects masked by σ₁₀. Two nominal density classes, corresponding to the EPS 100 and EPS 150 types, five recycled content levels (0%, 5%, 10%, 25%, 50% by volume), and 235 specimens were tested under EN ISO 29469:2022. A two-way ANOVA framework decomposed the recycling effect into source, content, and interaction components, with Welch’s ANOVA, classical ANOVA, and Kruskal–Wallis applied in parallel as robustness checks. Recycled content was the dominant factor across all metrics. The two types behaved differently with respect to source: EPS 100 showed an additive source effect throughout the dose range, while EPS 150 was dominated by a strong source × content interaction, with the sources equivalent at low doses and S1 substantially outperforming S2 at 50% substitution. A recycled fraction of 5% was statistically equivalent to virgin material in every configuration tested. The findings show that energy-based metrics resolve recycled material source effects that are not detectable on σ₁₀ alone, and that the substitution is type-specific rather than universal.