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Building Performance and Energy Efficiency
Published in Dorothy Gerring, Renewable Energy Systems for Building Designers, 2023
The component keeping the air in or out of the building is called the air barrier. The air barrier seals up the building envelope and reduces the amount of natural air exchange. Differences between inside and outside temperatures, wind, and the operation of fans and mechanical systems inside the building all create pressure across the building envelope. Any holes in the building will exchange air (leak) if they aren’t sealed up. Although you might think that there aren’t many holes in a building envelope, there can actually be many. In the past, for residential homes in the USA, fresh air was provided by air exchange through all these holes. Air is coming in one set of holes (infiltration) and exiting through another set of holes (exfiltration). You might say, “oh, that makes sense, it is important to have fresh air.” While it is true that fresh air is important, the problem with air leakage is that you have no control over how much or where air exchange is occurring, nor can you control the quality of the air coming in since it is randomly coming in from everywhere.
Sealants, Insulation and Barriers and How to Install Them
Published in Stan Harbuck, Donna Harbuck, Residential Energy Auditing and Improvement, 2021
If the rigid material is too air permeable, air barrier papers or films can be used. Staple the air barrier to the rigid material or the wood around it to seal the air barrier at the edges and seams. Cross-linked woven polyethylene films are examples of this type of air barrier. Polyethylene films and regular cross-linked polyethylene serve as both air and vapor barriers. Be sure to seal the overlaps and edges of the air barrier with the appropriate tape or sealant as specified by the manufacturer. If possible, sealants are preferred because tapes typically lose their adhesiveness over time.
Principles of Environmental Control in Building Envelopes
Published in Mark T. Bomberg, Joseph W. Lstiburek, Spray Polyurethane Foam in External Envelopes of Buildings, 2018
Mark T. Bomberg, Joseph W. Lstiburek
The air barrier controls flow of air through external envelopes of the building. However, the effect of pathways created by external cavities and interconnected internal cavities communicating with HVAC systems on performance of building systems is seldom recognized. The significance of these elements, mostly neglected in the traditional analysis of air pressure fields, will be illustrated in the few examples selected from case studies (Lstiburek, 1992, 1994,1995).
Application of passive measures for energy conservation in buildings – a review
Published in Advances in Building Energy Research, 2019
Farhad Amirifard, Seyed Amirhosain Sharif, Fuzhan Nasiri
Some materials due to their nature can be used as an air barrier and vapour barrier at the same time such as sheet metal and glass. Some materials, like sealed gypsum board, house wraps or wood sheathing, are effective air barriers but provide little water vapour diffusion control. Torn or unsealed polyethylene cannot be used as an air barrier but could perform well as a vapour barrier (Straube & Burnett, 2005). To determine the water vapour transmission properties of construction materials, two methods are commonly used: the dry and wet cup methods. The first method is associated with a mean relative humidity of 25% and the second method with a 75% relative humidity. Kumaran extended the cup methods at varying relative humidity levels and tested them for three materials: perlite insulation board, calcium silicate insulation board, and plywood sheathing (Petersen, Link, & Kumaran, 1998). Künzel (1999) evaluated the use of smart retarders by conducting field tests. According to the results, a smart vapour retarder will increase the moisture load tolerance of materials which can effectively decrease the risk of damage to the building envelope. Wilkinson, Ueno, De Rose, Straube, and Fugler (2007) tested below-grade and above-grade wall assemblies in southern Ontario with and without polyethylene sheeting to determine the pros and cons of each approach. Kumaran, Lackey, Normandin, and Van Reenen (2005) evaluated 18 building membranes (paper-based and polymer-based materials) that were available in North American markets as to their level of water vapour permeance, air permeance, and the water absorption coefficient. Saneinejad (2009) performed experimental research to assess hygrothermal performance under conditions leading to inward moisture flow. Based on the results, the presence of vapour tight interior finishes causes accumulation of moisture in the interior gypsum board. Moreover, a vapour tight sheathing does not prevent moisture accumulation in the interior gypsum board and the wood studs. Table 4 illustrates vapour retarder’s classification based on permeance and rigidity.