roof

One of a series of articles focussing on problem areas in buildings. 1) Examines condensation risks in buildings. Treats condensation processes, water vapour input and movement, conditions for surface and interstitial condensation in walls and roofs. 2) Treats condensation avoidance in general, humidity control, controlling vapour flow, adding insulation, heating, mould. Illustrates numerous examples diagrammatically from various building types.

Failure to understand the principles appropriate to a particular roof makes it all too easy to introduce condensation problems, often serious ones. A distinction between surface condensation and interstitial condensation is made. Before attempting work on any roof it is necessary to determine how the roof is designed to work. If the principles are wrong, the whole design should be checked and if necessary corrected.

Discusses problems of condensation in cavity roofs of industrial buildings, including ventilation air as a moisture source. Lists points to watch when foam filling the cavity.

Flat wood-frame house roofs with insulation applied between joists are susceptible to condensation problems in cold climates. Investigation of difficulties experienced in a wood-frame row housing project in Eastern Canada showed that many interrelated factors contribute to the occurrence of problems and demonstrated that control of air leakage through the ceiling is the one primary requirement for successful performance.

Roof space ventilation is important in warm weather to dry out moisture that may have accumulated in the roof space. It is important to reduce the movement of moisture from the living areas to the roof space and to ventilate the latter by means of vents distributed between the upper and lower parts of theroof to take advantage of both wind action and stack action.

Presents four short articles treating aspects of building ventilation: 1) Achieving a balance - the work of the AIC, 2) House full of horrors - indoor air pollution and progress in eradicating hazards, 3) Letting off steam - test houses with ventilation system for condensation control, and 4) High and dry - condensation in the roof, eaves to eaves ridge ventilation.

Buildings in cold climates must provide an indoor environment that is markedly different from that outdoors. The materials and components of the exterior envelope are subjected to large variations in conditions and greater demands are placed on the indoor environmental control system. Air pressure differences across building elements are augmented by buoyancy forces that influence air movement and indoor air quality. The potential for moisture condensation on and within the envelope is increased as is the danger of freezing in liquid systems.