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The Building Envelope: Primers from Environmental Building News

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Building envelopes involve a complex interplay between often opposing forces: daylighting and insulation or air-sealing and the ability to release moisture. The following primers from the pages of Environmental Building News explore six concepts around building envelopes, and offer strategies for designing for high-performance.

Thermal Mass—What It is and When It Improves Comfort: Heavy or massive objects like masonry, earth, and water can hold a lot of heat, and can be used to regulate temperatures in buildings. In the Southwest, for example, masonry walls can absorb heat during the day (keeping the inside cool) and release it during chilly nights (keeping the inside warm). Manufacturers try to claim high “effective insulation values” for these materials, however, despite the fact that they don’t actually insulate that well.

Building envelopes involve a complex interplay between often opposing forces: daylighting and insulation or air-sealing and the ability to release moisture. The following primers from the pages of Environmental Building News explore six concepts around building envelopes, and offer strategies for designing for high-performance.

Thermal Mass—What It is and When It Improves Comfort: Heavy or massive objects like masonry, earth, and water can hold a lot of heat, and can be used to regulate temperatures in buildings. In the Southwest, for example, masonry walls can absorb heat during the day (keeping the inside cool) and release it during chilly nights (keeping the inside warm). Manufacturers try to claim high “effective insulation values” for these materials, however, despite the fact that they don’t actually insulate that well.

Foam-in-Place Polyurethane Insulation: Among the many insulation materials we can choose from are foam-in-place products for filling cavities or creating a continuous layer on a wall or roof system. The most common of these is spray polyurethane foam, referred to in the industry as SPF. It is available in closed-cell and open-cell formulations, which differ in application and R-value.

Thermal Bridging: When materials with different thermal conductivities span from the warm side to the cold side of an assembly, more heat flow occurs through the material with higher conductivity. If the differences are large enough, that heat flow essentially short-circuits the insulation—a process referred to as thermal bridging.

Reducing Heat Flow Through Windows: Modern windows are much better than their old, single-pane counterpoints, but they still represent a compromise between thermal performance and daylight and views. Windows allow unwanted heat gain and loss through air leakage, conduction, and radiation. Low-emissivity coatings manage the radiation part of the picture.

Vapor Retarders and Air Barriers—Managing Moisture in Building Envelopes: Moisture from air can get into a wall cavity through air leaks or, in smaller quantities, by diffusing through a permeable material such as drywall, potentially causing mold and decay. Although many people conflate these two problems, there are in fact two distinct solutions: preventing air leakage with an air barrier and controlling moisture diffusion with a vapor retarder. Where you put these barriers matters, and varies based on climate and wall construction.

Solar Reflectance Index and Cool Roofs: Light-colored, reflective surfaces heat up less in the sun, making solar-generated cooling loads smaller in buildings with white, reflective roofs. These roofs also contribute less than darker roofs to the urban heat island effect, and are recognized by Energy Star, LEED, and other rating systems.

Continuing Education

Receive continuing education credit for reading these primers. The American Institute of Architects (AIA) has approved this course for 1 HSW/SD Learning Unit. The Green Building Certification Institute (GBCI) has approved the technical and instructional quality of this course for 1 GBCI CE hour towards the LEED Credential Maintenance Program.

Learning Objectives

Upon completing this course, participants will be able to:

    1. Explain how thermal mass helps maintain indoor thermal comfort in buildings.
    1. Describe the differences between closed-cell and open-cell spray polyurethane foam insulation.
    1. Define thermal bridging and describe three places where it can occur.
    1. Describe how windows contribute to unwanted thermal gain and loss, and what technologies mitigate their bad thermal performance.
    1. Explain the difference between an air barrier and vapor retarder, and describe how each is used.
    1. Explain the difference between emissivity and reflectivity and how each relates to roof performance.

To earn credit for this course, read the primers, then make sure you're logged into your personal BuildingGreen account, and pass this quiz. Please note: In order to complete the quiz portion of this continuing education course, you must click on the titles and read all the primers in full (not just the summaries shown here).

 

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July 17, 2010