condensation

The current German Standard specifies a minimum thermal insulation. However even with excellent insulation, if the air change rate is too low, condensation can form. High humidity emissions in dwellings can require air change rates of more than 2/hour. The use of mechanical ventilation, possibly humidity-controlled and with a heat recovery system, is suggested to minimize ventilation heat losses. The user has to be educated to provide adequate ventilation in spring and autumn, but during the cold season the ventilation rate can be reduced to two thirds of the minimum value.

The determining parameters for the formation of condensation are 1) the surface temperature of the building section and 2) the dew point temperature of the air in the room. Thermal bridges in intensively insulated outside walls and decreased ventilation due to tighter windows both increase the risk of condensation. Mechanical ventilation reduces the risk, but natural ventilation is dependent on occupant behaviour.

Over the last few years frequent cases of mould growth in dwellings have occurred. The problem is essentially due to an excessive moisture content of the building elements, which can result from hygroscopic adsorption or from frequent surface condensation.

Surface condensation and mould affect about 15% of the UK housing stock. This paper reports BRE work undertaken in occupied dwellings to identify the effectiveness of a range of remedial measures in various situations. The remedies investigated include the improvements to insulation levels, andheating systems, the provision of extract fans and dehumidifiers. The studies were undertaken in both flats and 2-storey houses, all of traditional construction with brick walls and pitched roofs.

Discusses case histories of rehabilitation work in flats and maisonettes in London, UK. It is clear from the results of these that the ventilation rate is inadequate for the lifestyle in the dwellings considered. Discusses provision of adequate ventilation by use of fans, vents and windows and use of thermal insulation.

Discusses ventilation efficiency and production rates of water vapour in residential buildings, using a three person flat of 100 m2 living area as amodel. The cold outer surfaces of a building are the critical ones regarding condensation. To avoid surface condensation, the ventilation requirement is that the air change rate must reduce the vapour content in the room air at least so far as to reduce the dew point temperature below the lowest surface temperature.

Summarizes the state of knowledge about combustion products, surface condensation and mould, formaldehyde and radon, and the guidance currently offered on their control in the UK. Statutory ventilation requirements are outlined and various measurement techniques described.

Final report on the performance of 177 low-energy houses at Pennyland, Milton Keynes, UK. Pressurization tests showed an air change rate of 0.3 ach for the Pennyland houses, compared to 0.7 ach for the control Neath Hill houses. Three quarters of the houses had some condensation and over a half had some mould growth.

A series of laboratory tests for moisture problems were conducted on an air infiltration barrier. One series involved the condition where warm and moist indoor air circulates through wall cavities. 

Notes that the trend to airtight window constructions has upset the balance in buildings between moisture generation and its removal. Treats the factors which combine to determine whether a building will have moisture problems. Presents a procedure for the straightforward determination of the specific minimum air flow required in a particular building to prevent condensation on the inner surface of corners formed by two dimensional external walls. Determines the base air flow and the supplementary air flow for four models of representative apartments.