Façade fires in tall buildings are currently occurring more than once a month globally that are responsible for many casualties and billions of dollars in losses. In particular, the tragic Grenfell Tower fire in London with more than 70 fatalities raised the profile of façade fire hazard. This work used well-controlled irradiation up to 60 kW/m2 to re-assess the fire hazard of typical flame-retardant aluminum composite panels (ACPs) with a dimension of 10 cm × 10 cm × 0.5 cm. We found that the vertically oriented ACPs with the “non-combustible” A2-grade and “limited-combustible” B-grade cores could still be ignited above 35 kW/m2 and 25 kW/m2, after the front aluminum layer peeled off. The peak heat release rate per unit area of these ACPs could be higher than common materials like timber and PVC. Moreover, compared to the B-core panel, the A2-core panel showed a greater fire hazard in terms of a shorter ignition delay time, a higher possibility of the core peel-off, and a longer flaming duration under current test size and fixing condition. Because the ACP is a complex system, its fire hazard is not simply controlled by the core material. The structural failure of ACP in fire, including peel-off, bending, softening and cracking, may further increase the fire hazard depending on the scale effect, boundary and fixing conditions. This research improves our understanding of the systematic fire behaviors of façade panels and helps rethink the fire risk and test methods of the building façade. Graphical Abstract: [Figure not available: see fulltext.].