Walls & Ceilings Architect/October 2007

Then, the activities and emissions of building occupants round out the list. Each living thing—person, animal or plant—occupying a building affects the energy efﬁciency of a building, as they all receive and radiate energy. These three elements are interconnected by three ﬂows: heat ﬂow, airﬂow and moisture ﬂow. Since the impact of thermal control within the building envelope has a large impact on a building’s sustainability, we will focus on the measure of heat ﬂow as it pertains to the structural components of the building. A thermally efﬁ cient building envelope creates an energy-efﬁcient building, spaces that are more comfortable and healthful for occupants and buildings that are more durable and longer lasting. HEAT FLOW Heat that ﬂows in and out of a building is a major factor in determining the comfort level and operating cost. Heat has a natural tendency to ﬂow from an area of high temperature to one of lower temperature. The greater the temperature difference, the faster heat transfers. During winter a heated building loses heat to the colder outside. Conversely, in the summer an air-conditioned building gains heat from outdoors. But, how can heat make its way inside and outside through solid exterior cladding and walls? There are three ways, actually—conduction, convection and radiation. In a building, these modes of heat transfer all occur at the same time and play an important role in the heat balance of a building. Conduction Conduction is probably the best known and the easiest to understand heat transfer process. It occurs when a material separates an area of high temperature from an area of low temperature, such as a wall. During the winter, the inside is warm and the outThis thermographic image of conduction through a divided glazing pane shows the transfer of heat side is cold. Only the between materials of different temperatures while wall separates the in direct contact. two extremes. The inside surface of the wall warms and tries to reach the same temperature as the air inside of the building. As the inside wall surface heats up, the adjacent material also warms, and over time, heat from the inside transfers through the wall to the outside. This results in heat loss from the building to the colder temperatures outside. The rate of heat transfer through the wall depends on two things. First, the temperature difference between inside and outside, and second, the nature of the material. Some materials transfer heat very well and are called conductors. Glass, concrete and all metals are examples of good conductors. Other materials, such as ﬁberglass and foam sheathings, transfer heat very poorly and are referred to as insulators. Convection Convection is the second most common mode of heat transfer. Heat transfer by convection occurs as a result of the movement of liquid or gas over a surface. Wind Base wall, 3-inch cavity. Best conﬁguration, 3-1/2-inch cavity. Best conﬁguration, 3-1/2-inch cavity. 26 | Walls & Ceilings Architect | October 2007 Illustrations courtesy CertainTeed Corporation

Table of Contents Feed for the Digital Edition of Walls & Ceilings Architect/October 2007

Contents Trade News Silver Certiﬁed Airtight The Men of Steel Thinking Thermal Firestop 101 ICFs Create a Tight Envelope The Finish Line The Green Thumb Cracking the Code

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