AIVC - Air Infiltration and Ventilation Centre

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condensation

Avoidance of condensation in roofs.

Sets out in general terms the design principles for avoiding condensation in roofs, pitched and flat. Recommends providing arain shield permeable to water vapour, a vapour barrier on thewarm side of the structure and in roofs with air spaces to ventilate the air space or blow dry air into the roof space.Discusses application of these to particular types of roofs.

Design and performance of roofs.

Surveys factors influencing roof design with respect to energy conservation. Discusses thermal insulation, condensation, ventilation and insolation.

Air leakage in buildings

Examines ways in which air leakage affects building performance. Heating load and building relative humidity in winter are affected by over-all air infiltration and ventilation rates. Windows and doors usually represent the major source of air leakage in buildings. Condensation problems occur when exfiltrating air deposits moisture on surfaces such as atticsand inside double windows. Discusses ways of reducing condensation. Finds that air tightness in inside of enclosure must always be many times greater than that of the outer cladding.

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.

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

Condensation risk and improved thermal performance of housing.

Considers the likely impact of alternative conservation measures on the incidence of surface and interstitial condensation on or within the elements of the building fabric. Considers specifically domestic buildings in temperate climates such as in the U.K. and Ireland. Outlines the mechanisms whereby condensation occurs and considers broadly the effect of reducing heating levels, reducing ventilation and increasing insulation.

Condensation between the panes of a double window

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.

Retrofitting an existing wood-frame residence for energy conservation-an experimental study

Describes retrofitting a wood-frame residence, having only limited insulation in the attic, to reduce its energy requirements for heating and cooling. The three retrofit stages comprised : reducing air leaks ; adding storm windows : andinstalling insulation in the floor, ceiling and walls. The housewas extensively insulated to evaluate energy savings and other performance factors. an economic model was used to evaluate the cost effectiveness of the retrofit options.

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.

The effects of ventilation and building design factors on the risk of condensation and mould growth in dwellings.

Presents calculations of mean temperatures and relative humidities , shown graphically for three typical housing types assuming different heat and moisture inputs: 1) whole house uniformly heated with moisture from household activities uniformly distributed; 2) kitchen at constant temperature with high moisture emission rate; 3) unheated bedroom with two occupants assumed to be in thermalequilibrium with a room below at 15 c. Concludes that there is a certain critical amount of heat needed to give a relative humidity of less than 70% and thus avoid the danger of mould growth .

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