Purpose: This study investigates how internal and external insulation affect the energy
performance of an existing multifamily building from the Swedish Million Programme era.
The aim is to evaluate how different insulation materials and thicknesses influence the
building’s energy use, heating demand, and compliance with the requirements of BBR 29.
Method: Dynamic energy simulations were conducted using IDA ICE 5.0. A detailed
building model was created and calibrated against measured data from the building’s energy
declaration to ensure realistic operating conditions. Three insulation materials—mineral
wool, expanded polystyrene (EPS), and polyisocyanurate (PIR)—were analysed in different
thicknesses (50, 100, and 150 mm). Both internal and external insulation scenarios were
evaluated. The study also examined the impact of increased window area and solar gains on
the building’s energy balance.
Results: The results indicate that all insulation measures reduce the building’s energy use,
with external insulation providing the most significant improvement. The greatest reduction
was achieved with 100 mm PIR insulation, which decreased total energy demand by
approximately 23% compared to the reference case. Increasing insulation thickness beyond
100 mm resulted in diminishing returns. Internal insulation showed lower energy savings
and introduced higher risks related to moisture and thermal bridges. The analysis also
showed that increased window area alone had minimal impact on heating demand, as higher
transmission losses were offset by solar gains. However, when combined with insulation,
solar gains contributed to improved energy performance.
Conclusion: External insulation is identified as the most effective and reliable strategy for
improving energy performance in the studied building. A thickness of approximately 100 mm
provides an optimal balance between energy savings and material efficiency. The study
highlights the importance of considering insulation, solar gains, and building envelope
performance as an integrated system. Properly calibrated simulation models, such as IDA
ICE, are shown to be valuable tools for evaluating energy efficiency measures in existing
buildings.