Purpose: Crawl space ventilation became essential to avoid moisture damage. Historical houses with wood floor and crawl spaces unventilated correctly often face problems of biological degradation. This paper seeks to address these issues. Design/methodology/approach: In this work a case study of the Egas Moniz museum house, in Estarreja, Portugal, with different building pathologies, such as biological degradation and development of micro-organisms and fungi, is presented. An experimental campaign was carried out with continuous monitoring of the relative humidity and temperature, to validate the real climatic conditions in the crawl spaces. Additionally, the authors analyse the treatment technologies used in the past and the characteristics of the rehabilitation solutions in order to control the hygrothermal behaviour. Simultaneously, numerical simulation was done using the software tool WUFI-2D to simulate the hygrothermal building behaviour and a sensitivity study of parameters used was done. Findings: The in-situ experimental results showed that high values of relative humidity imply biological degradation of the wood floor and the numerical and analytical models used showed the same tendency. The numerical results showed the importance of crawl spaces with a good ventilation to avoid mould growth and, also, suggested that controlled mechanical ventilation is preferable to strongly continuous mechanical ventilation in this type of spaces. The experimental study shows that the continuous functioning of a ventilation system may lead to the occurrence of interior condensation, so a hygro-regulated system is thus essential to control unwanted condensation, with an appropriate functioning criterion. Practical implications: In accordance with the numerical and experimental results, the authors proceeded to the implementation of a hygro-regulated system to ventilate the crawl spaces of the Egas Moniz museum house. Originality/value: This paper presents a new proposed intervention methodology, in crawl spaces, to avoid mould growth, based on an extraction controlled by a hygro-regulated ventilator. © Emerald Group Publishing Limited.