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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.

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.

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.

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.

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.

Rising damp affects the deterioration and conservation of architectural heritage. Air cavities built next to the base of these buildings on an unsaturated floor can reduce the damage to foundations and walls due to this. These are passive systems, which are usually designed with no objective data to show their functioning and effectiveness. This is why the authors are presenting this study.

This study is presented starting with simple field equipment for representative types for a previous cataloguing of cases in Spain. The physical parameters of the air in this research are air speed and evaporation in the cavities and the base, taking the local climate and the particular formal and construction characteristics of each case study as a reference.

The results of the analysis validate the method and the efficiency of such cavities, whose performance is greater in systems with a variety of features, that is to say, those which work by thermal or wind flow rather than those which only use hygric flow.

This work is novel because there are not in situ experimental works which prove the functioning and effectiveness of these systems.