Air Gap Method: drying of a concrete slab on ground construction

Purpose - The purpose of this paper is to report on a study which has been carried out on a timber floor construction above a ground-supported concrete slab, which was used in small detached houses built in Sweden during the period 1960-1990. This method of building has turned out to be a risky construction nowadays, but there are 800,000 houses built this way in Sweden.Design methodology approach - By using the patented Air Gap Method inside building constructions, harmful water can be dried out. The method ventilates air gaps inside walls and floors with an air flow driven by thermal buoyancy caused by a heating cable in the vertical air gaps. The drying out process has been studied both by measuring the moisture level in the slab and also by measuring the humidity transport and comparing this with air flow measurements.Findings - The paper shows that the Air Gap Method manages to dry out water from both the slab and the overlaying wooden construction. The study shows also that the relative humidity (RH) levels in the air space below the floor are reduced in a significant way, thus minimizing mould growth. It is also shown that a thin layer of concrete upon floor beams prevents mould to grow even in a humid situation.Research limitations implications - The research reported in this paper is only concerned with timber-framed small detached houses. Similar studies of apartment buildings are ongoing.Practical implications - The Air Gap Method can thus be useful in the context of renovating a water damaged house of this type built during this 30-year period. The method provides a possibility of drying out such damage without a separate drying period. The inhabitants could therefore be able to use a renovated water-damaged kitchen six eight weeks earlier compared to ordinary building methods.Originality value - The paper is useful because it provides better understanding of the mechanism of RH inside a building construction and how this parameter could be lowered. The paper is also useful in the context of renovating water-damaged small detached houses built by the risky method of construction used in the last decades of the twentieth century.