Built-up roofing assemblies are applied on jobs over a variety of substrates in all types of weather. Too often the roofing specifications are the bare minimum with design details favoring aesthetics at the expense of good roofing practice. Too often unplanned obstacles and traffic over the roof during construction cause costly delays and damage. All these factors add appreciably to the problems of the roofing contractor.
However, one of the major problems experienced by the roofer is adverse temperature conditions. Roofing contractors know that it is more difficult to apply good roof during the cold winter months than it is during warm weather, and most will not apply roofs below specific temperature levels. However, temperature alone is not the only criteria, Other weather factors must be considered – – wind, humidity, precipitation and sunny or cloudy skies.
Generally, it is agreed that uncoated felts are more flexible in cold weather that coated felts. It is also generally agreed that roofing asphalt can be applied at a lower ambient temperature than roofing pitch. In order to construct a sound roof membrane it is vitally necessary that the heated bitumen be applied while at relatively high temperature levels. During roofing application, cold weather, accompanied by wind, can result in rapid chilling of the heated bitumen. The combined effect of a given wind velocity at a given temperature can be measured using a Wind Chill Index.
Many roofing contractors in Canada are using this index to determine if the conditions are suitable for roofing application. To assure the application of a good roofing, the designer would be wise to determine basic minimum suggested application wind chill temperatures from his respective provincial roofing contractors.