Air barriers and building codes
Since a well-designed and properly installed air barrier system can dramatically improve a building’s energy efficiency, durability, and IAQ, it is unsurprising governing bodies require air barrier standards in building codes.
Building energy codes are minimum requirements for energy-efficient design and construction for new and renovated residential and commercial facilities. The expected trend is for all building codes to migrate toward standards mandating more energy-efficient design and construction.
The 2011 National Energy Code of Canada for Buildings (NECB) provides minimum requirements for the design and construction of energy-efficient structures and covers the building envelope, system, and equipment for HVAC. This code is similar to American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, which is already in use in some Canadian jurisdictions.
NECB is for new facilities, as well as substantial renovations in existing ones. It does not apply to farm buildings or to housing and smaller structures covered in NBC Part 9, “Housing and Small Buildings.” Further, Model National Energy Code for Houses (MNECH) provides technical requirements for energy-efficient house construction. This code applies to single-family houses of three stories or less and to additions of more than 10 m2 (108 sf).
An example of air barrier language found in ASHRAE 90.1 specifies air barriers be designed and noted in the following manner:
- all air barrier components of each building envelope assembly must be clearly identified or noted on the construction documents;
- the joints, interconnections, and penetrations of air barrier components, including lighting fixtures, need to be detailed or otherwise noted;
- continuous air barrier must extend over all surfaces of the building envelope (at the lowest floor, exterior walls, and ceiling or roof); and
- the continuous air barrier needs to be designed to resist both positive and negative pressures from wind, stack effect, and mechanical ventilation.
It also requires certain areas of the continuous air barrier be “wrapped, sealed, caulked, gasketed, or taped in an approved manner,” such as joints, junctions, penetrations, seams, transitions, and connections between different air barrier materials.
SPF as an air barrier
When trying to conform to Canada’s airtightness standards, it can be difficult to comply with the progressive requirements when using traditional air barrier materials. However, for many reasons, SPF insulation can be an ideal air barrier material because it consistently addresses the major concerns in both air barrier and insulation systems.
Some of the direct advantages of using SPF as an air barrier material instead of traditional materials include:
- ccSPF has an average rating of R-6 per inch, providing effective insulation properties within the building assembly (ocSPF has an R-value of 3.7 per inch);
- minimized water intrusion and condensation into the building due to ccSPF’s low water vapour permeability, low liquid water absorption, and high thermal performance;
- provide complete and continuous coverage around the building envelope (i.e. foundation and slab, walls, and roof) means SPF can minimize thermal bridging caused by fasteners, joints cracks, load shifts, and penetrations into the structure; and
- ccSPF can significantly increase the buildings’ structural integrity when compared to traditionally insulated buildings.
Conclusion
When buildings are tightly constructed, one can no longer count on ‘fresh air’ ventilation to naturally occur through gaps and cracks in the structure. Therefore, HVAC contractors must take control of the ventilation through mechanical means. One good place to consult for ventilation guidance is in ASHRAE 62, Ventilation for Acceptable Indoor Air Quality. Tight construction and mechanical ventilation that can be filtered and pre-conditioned will provide superior IAQ compared to random, uncontrolled natural ‘ventilation’ through air leakage.
Air barrier materials, assemblies, and systems are a critical part of energy efficiency in residential and commercial construction. Without a well-designed and complete air barrier, buildings can suffer from excessive air infiltration and exfiltration that can compromise the air quality, durability, and comfort of living environments.
Although there are many air barrier options, many traditional materials no longer satisfy the increasingly stringent requirements for energy efficiency because they are often not installed well enough to be airtight. Sprayed polyurethane foam insulation, however, continues to prove suitable due to its flexible installation and ability to create a continuous air barrier around the entire structure.
Andrew Hunt is the vice-president of Confluence Communications, which creates outreach and communication materials specifically designed to promote energy-efficient building practices and technologies in the residential and commercial construction market. He can be reached via e-mail at andrew@confluencec.com.
Monica Karamagi is the regional marketing and industry affairs manager for the polyurethanes division of Huntsman Corp. She has a bachelor’s degree in chemical engineering from Texas A&M University, and a master’s degree in chemical engineering from Howard University (Washington, D.C.). Karamagi is currently a member of the Spray Polyurethane Foam Alliance (SPFA) board of directors, and leads the Energy Efficiency Task Group in the rigid foam committee of the Center of the Polyurethanes Industry (CPI). She is also an active member of North American Insulation Manufacturers Association (NAIMA). Karamagi can be contacted at monica_n_karamagi@huntsman.com.
