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The rates of moisture production and removal determine the humidity level in houses and the likelihood of condensation problems. Causes and cures of these problems are reviewed.

Heating load and building relative humidity in winter are affected by over-all air infiltration and ventilation rates. Since windows and doors usually represent the major source of air leakage in buildings, significant reductions of overall air infiltration are achieved principally by increasing the air-tightness of these components. Reduction of the air infiltration rate through windows, however, will not reduce exfiltration through other cracks and porous condensation. To overcome condensation problems resulting from exfiltration, cracks and porous construction must be eliminated on the warm side of the structure. In multi- story buildings air flow between floors should be restricted to reduce pressure differences resulting from chimney action.

This Digest attempts to outline the principles involved in approaching the problem of dripping in curling rinks, and to discuss some of the methods that might lead to a solution. The analysis suggests that some means of introducing heat into the building is probably the most generally applicable and effective condensation control, particularly in the colder areas in Canada. In conjunction with heating, a roof deck having some thermal insulation value should be used for reasons of heat economy and to provide maximum ceiling surface temperatures. Ceiling finishes having water- absorbing characteristics offer considerable advantages over finishes incapable of taking up moisture. Wood roof decking is an ideal ceiling finish as it not only provides thermal insulation but is also capable of absorbing water.

Comfort conditions for the users of indoor swimming pool rooms are discussed establishing the thermal and moisture conditions to be expected in these spaces. The implications of these conditions and their effects upon the building fabric are discussed with some suggestions for the design of trouble-free enclosures being offered.

Interior surface temperatures at the edges of sealed double- glazing units are lower than those of many conventional double window arrangements, and the building humidities that can be carried without excessive condensation on these surfaces are correspondingly lower. They must be sealed initially with dry air between the panes, and in spite of the stresses imposed by service conditions must retain the seal over their required service life. Units can fail by either breakage or condensation and the scumming that results from excessive moisture gain. On the other hand, sealed glazing units have advantages in the elimination of storm sash, reduction of surfaces that need cleaning to two, and prevention of condensation between panes. These may often outweigh the potential problems in their use.

Some problems that have developed in walls which incorporate precast panels in the conventional manner are described. The underlying causes are explained and shown to be linked to a basically faulty concept of wall design.

This Digest describes a method whereby the designer can choose and position his materials so that harmful accumulation of water resulting from diffusion can be prevented.