roof

Aerodynamic phenomena affecting the ventilation process, such as aerodynamic mixing, generation of secondary and slightly turbulent flows, roof contours, infiltration and convection and their connection with geometric parameters of the object and energy expenditure for ventilation are analysed.

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

A previous paper analysed a mathematical model of a non-condensing cavity. This paper extends the analysis of the first paper to analyse the seasonal moisture behaviour of a condensing building cavity. Climate statistics are used to calculate the duration of the winter wet-up period, and a rate of condensation formula is integrated to give total winter condensation. Although engineering design calculations cannot yet be attempted, some illustrative examples are given based on field data. The results give preliminary verification of the model analysed in both papers.

This paper, the first of two, presents a conceptual model of moisture concentrations in a building cavity. The model is comprehensive and general considering air infiltration, vapour diffusion and material hygroscopicity under non-steady state conditions. The resulting linearised coupled differential equations are analytically solved to study the case of long term cavity moisture behaviour. Dimensionless parameters and algebraic formulae are presented describing all important moisture performance parameters for a non-condensing cavity.

Evidence of the importance of air infiltration in moisture control in building structures has been steadily accumulating. A general model of moisture behaviour in structures has been built up including for the effects of cavity air leakage, for the hygroscopic behaviour of timber, for the effects of condensation and various geometric factors.

The heating and cooling loads due to air infiltration may be estimated by a mathematical model that requires knowledge of the leakage characteristics of each component of the envelope. To extend the modelisation to the pitched roofs common in Portugal, characteristics of roofs were determined by a differential pressure method.

Moisture enters an attic both from the house and from the ventilation air. It has been assumed that when the roof sheathing temperature cools below the attic air dew point, condensation occurs on the roof sheathing. If this were true, then increased attic insulation levels would require increased attic ventilation rates. Results from an experimental study are presented which show that in fact the roof sheathing is in dynamic equilibrium with moisture in the attic air, and that several hundred pounds of water can be stored in the attic wood without ill effects.

Examines the causes of condensation problems and ways of reducing or eliminating them. Deals with diffusion through the building envelope, mechanical dehumidification and ventilation. Considers condensation inside cavities and roof spaces.

Measures the pressure on the outlet of a flue on a free-standing scale model in the wind tunnel at IG-TNO, as a function of the height of the flue outlet above the roof, of its position on the sloping roof and the pitch of the roof.

One of a series of investigations of the improper functioning of ventilation and smoke stacks. The problem is essentially one of town planning in which the layout of low and high rise buildings can cause unknown influences at the outlet of vertical stacks on low rise buildings. The study concerns thepressure distribution on and above the roof of a low rise building upwind or downwind of a high rise building as a function of the separation between them for various heights of the high rise buildings.