Building energy assessment of conventional and sustainable wall systems for realistic net zero energy buildings (RNZEB)

The building sector is a major contributor to global energy consumption and carbon emissions through both operational energy demand and the embodied carbon of construction materials. While Net Zero Energy Building (NZEB) concepts focus mainly on reducing operational energy, the Realistic Net Zero Energy Building (RNZEB) framework additionally incorporates embodied carbon into lifecycle sustainability assessment. However, few studies have compared the influence of different wall materials on lifecycle environmental performance under a single geometry-controlled RNZEB workflow. This study evaluates and compares the sustainability performance of three residential wall systems: conventional Brick Walls (BRW), Lightweight Concrete Block Walls (LWCBW) and Timber Walls (TW). A detailed Building Information Model (BIM) of a G + 1 residential building was developed in Autodesk Revit, and Autodesk Forma Carbon Insights was used to estimate embodied carbon, operational carbon, total lifecycle energy and Energy Use Intensity (EUI). Three separate wall-material models were created while keeping building geometry, dimensions and orientation identical to isolate the effect of the wall material. Lifecycle assessment was performed for 1-year, 10-year and 20-year periods. Carbon (kgCO₂e) is the primary quantity reported throughout; the kilowatt-hour figures are uniformly-scaled, carbon-derived energy-equivalents presented only as secondary indicators for cross-material comparison, and they are distinct from the simulated operational energy from which the Energy Use Intensity is obtained. Results show that operational energy dominates lifecycle impacts over long horizons, while embodied impacts remain fixed after construction. Within the assumptions and the software framework used, the Timber Wall system returned the lowest modelled lifecycle carbon, about 2.28% below brick and 2.89% below lightweight concrete block corresponding to the lowest 20-year carbon-derived energy-equivalent of approximately 3.25 × 10⁶ kWh. On operational Energy Use Intensity (EUI) the three systems were essentially equivalent (within about 3.3%), with timber marginally highest; timber’s lower modelled lifecycle total is therefore driven by its lower embodied carbon and not by any demonstrated operational advantage; the 2–3% differences are best read as screening-level indications obtained within the adopted software framework and the A1–A3 plus B6 lifecycle boundary, rather than as definitive evidence that any one wall system is superior. The findings support Sustainable Development Goals 7, 9, 11, 12 and 13 by promoting energy-efficient, low-carbon residential construction through BIM-integrated RNZEB assessment.