Treatment of Rising Damp in Historical Buildings

Abstract

Humidity is one of the main causes of decay in buildings, particularly rising damp, caused by the migration of moisture from the ground through the materials of the walls and floors via capillary action. This water comes from groundwater and surface water. The height that moisture will reach through capillary action depends upon factors such as the quantity of water in contact with the particular part of the building, surface evaporation conditions, wall thickness, building orientation and the presence of salts. In historic buildings, rising damp is particularly difficult to treat, due to the thickness and heterogeneity of the walls. Traditional methods of dealing with this problem (chemical or physical barriers, electro-osmosis, etc.) have proved somewhat ineffective. There is therefore a need to study new systems. In recent years, experimental research into the effectiveness of wall base ventilation systems (natural or hygro-regulated) to reduce the level of rising damp, conducted at the Building Physics Laboratory, Faculty of Engineering, University of Oporto, has yielded interesting results. Numerical simulation studies, using the software WUFI-2D, have given similar findings. This paper describes a new system for treating rising damp in historic buildings based upon a hygro-regulated wall base ventilation system, and analyses the results obtained following implementation of the system in churches in Portugal. It was defined criterions to avoid condensation problems inside the system and crystallizations/dissolutions problems at the walls.