Abstract: What is radiation; which part of it is involved in durability problems; how does it affect the organic materials used in and on buildings? Ultraviolet light between 350 and 300 nm is shown to be the most damaging radiation. It acts by changing the chemical structure of the polymers used in organic building materials, consequently affecting their physical properties. Fortunately, the intensity of destructive UV is a small part of the total solar radiation and is reduced as the angle of the sun decreases and by clouds and smoke. Unfortunately, enough UV is received on the surfaces of buildings to cause degradation of materials, particularly when it acts in conjunction with oxygen, water, heat or a combination of these elements.
Abstract: This Digest discusses how radiation affects organic building materials when its action is associated with the action of other elements of weather. Because the severity of damage is increased with the combined attack, preventive action must be taken to reduce degradation to an acceptable level. This includes production of polymers unaffected by UV or incorporation of compounds that reflect or absorb UV. Although these steps are normally in the hands of the material producer, building designers should be aware of their importance and of the limitations they may place on performance.
Abstract: Masonry of excellent quality can be laid up using traditional cold weather procedures that do not meet requirements in the National Building Code of Canada. Explanations based on the nature of the materials and some of the critical parameters are examined.
Abstract: This Digest discusses the organisms responsible for biological attack, the reasons for it, the conditions that lead to it, and the organic building materials that are subject to it. The qualitative prediction of deterioration through biological action is difficult because of the many factors involved and the variability of environmental conditions. The manufacturer is best able to provide the basic information relating to his product. Designers and builders must be aware of the nature and likelihood of biological attack in order that optimum selection and application of materials are achieved.
Abstract: Problems with cladding are frequently the result of movement of supporting concrete building frames due to creep and shrinkage, a source of trouble that is often not recognized. Although frame deformation is frequently the prime cause, diagnosis is difficult owing to the fact that workmanship, materials, moisture, temperature and design factors aggravate the situation. The physical and chemical mechanisms involved in creep and shrinkage as natural phenomena were discussed in CBD 119. It is the purpose of the present Digest to draw particular attention to their effects on cladding.
Abstract: Orientation influences the severity of the exposure to which walls are subjected. Temperatures at any given time can vary as much as 90 degrees due to solar radiation; and the number of freeze-thaw cycles can subsequently be increased as the result of solar radiation. Wetting of walls, as influenced by prevailing winds and air leakage patterns, is also of significance with respect to the environment in which materials must serve.
Abstract: Porous materials such as stone, brick, concrete and wood are far from being the simple materials their extensive use suggests. Understanding of their structure is essential, therefore, if reliable prediction is to be made of their response to various conditions of exposure.
Abstract: This Digest is intended to draw attention to the problem of foundation heave resulting from adfreezing for such structures as attached garages and carports, basement garages, separate garages, unheated warehouses, cottages and mechanical and electrical service units sensitive to differential movements.
Abstract: Both panes of factory-sealed double-glazing units are susceptible to thermal breakage. The outer pane experiences large thermally induced stresses when solar radiation falls on the sealed unit in cool weather. The breakage potential is even greater for units with heat-absorbing or heat- reflecting glass in the outer pane than for units with a clear outer pane. The inner pane experiences a high thermal stress when the outdoor air temperature is very low and the unit is subjected to localized heating. The breakage potential of the inner pane is greater for heat-reflecting units with a low U-value than for clear, heat-absorbing, or high-emissivity heat-reflecting units. Measured and calculated values of thermal stress for inner and outer panes of sealed glazing units indicate that thermal stress by itself should not cause glass breakage. Extensive breakage failure will only occur if the thermal stress is augmented by other tensile stresses or if weak or damaged glass is used. In the absence of a reliable method of predicting the probability of thermal breakage in sealed units, however, all factors that can possibly reduce the potential for breakage should be accommodated in design. This is especially true for units with heat-absorbing and heat-reflecting glass.
Abstract: The performance of building materials depends to a large measure upon the conditions of moisture to which they are subjected, involving both the levels of moisture content and their cyclic changes. It is in the interest of the designer and specifier to be aware of the factors involved and to have an understanding of the processes if optimum performance of materials is to be achieved.
Abstract: Masonry surfaces can be successfully painted if the correct type of coating is used for the substrate in question and if good design and construction have prevented leaks and openings in the structure. In such cases, coatings not only improve the appearance, but also give some protection by preventing rain penetration. If a wall remains dry its thermal conductivity is retained and it may not be subject to other problems associated with wetness. When design or construction practices are faulty, organic coatings cannot be expected to remedy the situation.
Abstract: The choice of glass thickness for windows has always been one of conventional practice. This digest presents information regarding glass strength and wind pressure characteristics. It is now possible to incorporate this information in an improved procedure for determining appropriate glass thicknesses for windows of different sizes subjected to different wind pressures.
Subject: windows; glasses (materials); strength of materials; thickness; wind loads; design loads; cost benefit analysis; Windows : Glass thickness for windows
Canadian Building Digest; no. CBD-132, ISSN: 0008-3097, Publication date: 1970-12