A brief synopsis of recent analytic and experimental studies is given. Conclusions are that convective transfer of water vapour into an attic from the living space below often transports more moisture than diffusive transfer through the ceiling construction. Large quantities of moisture are stored in the roof sheathing during warm spring and summer periods. Solar loading during mild winter periods can produce desorption of moisture from the sheathing. This paper reviews the formulation of mathematical relationships among physical parameters governing moisture transfer within attics.
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.
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.
This report addresses the factors causing water vapour problems and provides insights into the solutions available with particular emphasis on vapour barrier paints. Concludes that 1. moisture flow in structures is a dynamic, systemic process of multiple variables, and therefore requires an integrated approach for management, 2. retrofit applications offer an entirely different set of physical and economic considerations than are found in new construction and therefore require a different approach, 3.
When indoor air concentrations from indoor combustion processes are estimated, source strengths and ventilation rates are usually considered. Recent studies, conducted in the Energy Research House at Iowa State University, indicate that seve
Roof space ventilation is necessary to evacuate water vapour to avoid condensation and to conserve the wooden roof supports. It has been affected by 1. increased insulation, 2. snow screens fitted under the roof, 3. increased humidity due to
For the transient analysis of the thermal and moisture conditions in multilayer constructions a numerical algorithm and a computer program based on the Crank-Nicholson method and quasi linearisation are formulated. Temperature and moisture content are used as transport potentials. In energy balance equations and conditions, convention and accumulation of moisture, the diffusion flow of water vapour, the capillary and surface diffusion flow of liquid water and the viscous flow of humid air and water are considered. The boundary layer and interfacial balance equations are derived.
Uses a multi-channel infra-red gas analyser to measure nitrous oxide tracer gas concentration at six points round a house. Combines concentrations to give overall house ventilation rates and to estimate the air exchange between individual rooms. The gas analyser is also used to measure air movement between the house and its roof (with 5 sampling points in the house and one in the roof). Results show that typically 20-30% of the air that enters a houseleaves via the roof space through gaps in the ceiling.
Calculations of water vapour flow through walls and ceilings are frequently based on the permeability of building materials and implicitly assume that most of the vapour transport takes place by diffusion. Finds that this model is generally inval
Discusses causes of condensation between the panes of a double window. Treats movement of water vapour by diffusion and by air leakage separately. Describes tests made to determine air flow and vapour diffusion through test windows finds that relative importance of the mechanisms depends largely on the inside to outside pressure difference so that the higher the pressure difference, the greater the importance of air leakage. Suggests venting of windows to overcome condensation.
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