Empirical and computational evidence for thermal mass assessment: The example of insulating concrete formwork

•First evidence base of the transient thermal behaviour of ICF.•ICF's thermal mass was the most sensitive parameter affecting internal temperatures.•ICF's concrete core not decoupled from interior, showing high thermal inertia.•ICF reduces transmission losses by 37% compared to lightweight construction.•ICF could lead to higher overheating risk compared to heavyweight construction.