Fire in houses are a significant hazard often resulting in loss of life and substantial repair costs due to damage to the structure and contents. There is a clear need to prevent its ignition and spread to adjacent areas. This article presents the steps taken, namely: contacts, data collection, tests, analysis, and conclusions regarding the accident resulting from the outbreak and spread of a fire, on December 25, 2020, in a traditional Portuguese house in Arganil, Portugal. An expert with specialized technical-scientific knowledge was requested to conduct this investigation, which involved observations and data analysis followed by laboratory tests the work consists of carrying out observations and data analysis. Then, the observed and analysed data were laboratory tested to consistently identify characteristics that lead to the ignition and propagation of the fire. This work identified construction problems, materials used and heat sources that are responsible for the accident. The conclusions may be used to avoid future incidents or accidents with houses of same construction type.