Production-stage life cycle assessment of core materials for structural insulated panels used in building façades

Structural insulated panels (SIPs) are increasingly used in energy-efficient building envelopes, but their environmental performance depends strongly on the core material. This study assesses the production-stage environmental impacts of alternative SIP core materials developed from Portuguese industrial by-products: low-calcium fly ash (FA), municipal solid-waste incineration slag (MSWIS), and marble waste powder (MWP). Three selected alkali-activated formulations were compared with two reference solutions: expanded polystyrene (EPS) and a Portland-cement-based lightweight core. A cradle-to-gate life cycle assessment (A1–A3) was performed using SimaPro, the ecoinvent database and the ReCiPe Midpoint (H) method. The functional unit was 1 m² of SIP core material with a thickness of 150 mm. The results showed considerable variation among the waste-based formulations. The best-performing waste-based option was fly-ash based, whereas the highest-impact formulation was penalised by higher mass per functional unit and greater sodium hydroxide demand. Across the waste-based alternatives, sodium silicate solution, sodium hydroxide and, where applicable, accelerated curing were the main environmental hotspots. EPS showed the lowest impacts overall, mainly because of its very low density and reduced material demand. The results show that using industrial by-products does not automatically ensure lower environmental impacts. Future optimisation of waste-based SIP cores should prioritise density reduction, lower-impact activator systems and reduced curing energy demand.