AIVC - Air Infiltration and Ventilation Centre

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moisture

A field study of moisture damage in walls insulated without a vapour barrier.

Describes the results of a major study to find out whether or not wall insulation installed without a vapour barrier causes an increased risk of moisture damage within walls. The exterior walls of 96 homes in Portland, Oregon were opened. Presents results of field and laboratory tests which show the absence of indications of moisture damage. Gives data on shrinkage and settling of insulation and results of air leakage measurements by fan pressurization tests. Concludes that the addition of wallinsulation without a vapour barrier does not cause moisture damage in existing homes.

Moisture in a timber-based flat roof of cold deck construction

Reports tests made to examine moisture problems in a flat roof of cold deck construction. Tests simulated the effect of normal, wet and very wet conditions below the roof with no ventilation of the roof. Found that without ventilation there is a substantial risk of moisture degrade and condensation problems. Roof was then ventilated at five air changes per hour and this was found to be effective in solving moisture problems. Suggests this as a minimum ventilation rate and that where it is difficult to provide ventilation in a flat roof, a warm deck design should be considered.

Influence of mechanical ventilation on moisture content of bathroom air.

Reports experimental investigation of moisture content of bathroom air during and after a shower. Describes test apparatus and procedure. Gives graphs of dry and wet bulb temperature, relative humidity and absolute humidity for various mechanical ventilation rates as functions of time. Gives results of measurements of tracer-gas decay rates for various mechanical ventilation rates. Presents theoretical model for calculations of moisture content in air in bathrooms and finds excellent agreement with experimental data.

Jointing system for outer walls. Fogtatningssystem for yttervaggar

The building industry has always had considerable difficulty with joints in outer walls, at windows, doors and between building units. Damage caused by damp has meant considerable economic losses. New building methods and materials and stronger requirements in the indoor climate have accentuated the problem. Discusses use of fibreglass strips as a sealing agent. These can accommodate large movements in the joints, but the hermetic sealing properties are insufficient if there is a heavy damp load on the joint. Glass combined with plastic sheet can increase the hermetic sealing.

Condensation in attics : are vapor barriers really the answer ?.

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

Cavity barriers and ventilation in flat and low-pitched roofs.

Reviews the requirement in building regulations for cavity barriers in roofs. States need for providing ventilation in the cavities of certain forms of roof construction,particularly those with a continuous waterproof vapour barrier to avoid moisture build-up. Examines how adequate air movement can be provided in both new and existing flat roof voids, designed with or having installed cavity barriers.

Fundamentals of moisture and energy flow in capillary-porous building materials

Discusses basic physical features of combined energy and moisture flow in porous building material. Discusses mathematical and physical structure of these dynamic processes in terms of local thermodynamic equilibrium, flows induced by gradients in intensive state variables and conservation of energy, moisture and other components. Gives conditions for thermodynamic equilibrium, discusses peculiarities of pore-water tension, and problems concerning energy flow. Deals with the causes of hysteresis and the complications due to hysteresis.

Heat and moisture flow through openings by convection

Gives equations and charts for the calculation of heat and moisture flow due to natural convection through openings in vertical partitions separating spaces at different air conditions. Finds that heat and moisture transfer coefficients depend on the Grashof number and to some extent on the ratio of opening height to thickness. Also gives chart and equations for flow across an opening in a horizontal partition when the higher density air is above the opening.

Moisture accumulation in walls due to air leakage.

A number of cases of water and frost damage in masonry and non loadbearing walls have been examined. This damage could not have resulted from vapour diffusion or rain penetration and is primarily caused by condensation due to exfiltration of air. Air exfiltrates through the many cracks and joints and in this connection the result of chimney action and wind is explained in some detail, including the pattern and magnitude of building pressure differences that induce ex-filtration together with a discussion regarding the moisture that is transferred.

Intermittent ventilation of domestic premises from the energy aspect. Die Stosslufting von Wohnraumen aus energetischer Sicht.

Discusses oxygen requirements and moisture emission of individuals and generation of CO2, odours, and aerosols in inhabited rooms. Treats calculation of hygienically necessary air flow rates. Notes characteristics of continuous andintermittent ventilation, whereby additional outside air is discharged into a room at set intervals when continuous airflow rate falls below hygiene requirements. Compares hygienically adequate, continuous ventilation with intermittent ventilation by calculating hygienically-necessary outside air flowrate using a mathematical mode.

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