By Rick Scott, AIA
This is part 4 of 4.
Conclusions and Lessons Learned
Test findings showed the difficulty of trying to achieve a very tight air barrier installation. While the resort specifications called for a very ambitious whole building air barrier performance target of 0.085 cfm/ft2 at 75 Pa, such numbers are almost meaningless to the workers performing the air barrier assembly installation. These target numbers are probably abstract to many designers as well.
Rather than providing performance specifications, the designers needed to provide prescriptive specifications with directions to the workers on proper installation techniques to achieve the target air tightness.
The specified target number was also much tighter than ASHRAE 189.1 and IgCC air tightness requirements. These less stringent standards were not applicable to this project. However, of the three tested rooms:
- Only one met the ASHRAE 189.1 air infiltration requirement of 0.40 cfm/ft2.
- None met the IgCC air infiltration requirement of 0.25cfm/ft2.
The air tightness goals set by the design team were overly optimistic for the air barrier assembly specified for the project. A lower number would be acceptable when combined with a properly designed, installed, and functioning HVAC system that provided adequate positive pressurization and dehumidification. During the design peer review of the HVAC system, it had been noted that as designed, it was capable of achieving sufficient positive building pressurization and dehumidification with the actual as-built condition air leakage discovered during testing.
Lessons learned from air barrier testing at this tropical resort, as well as at many other building sites, include the following:
- Specify reasonable and achievable air barrier requirements. Understand the limits of materials, code and industry requirements, and climatic needs.
- Provide better directions to workers on air barrier assembly installation. It is the small details that count, and a prescriptive approach is better than a performance approach.
- Specify construction phase air tightness testing. A prescriptive approach alone may not be sufficient, especially in extreme climates
- Perform better quality control (QC) inspections of air barrier assembly installation, especially at critical phases. Develop checklists and document.
- Test sliding glass doors for air leakage during the specified water intrusion tests and compare to specifications and manufacturer’s data. Document tests, including videos.
- Perform blower door testing at lower floors after dry-in. Catch problems before the entire envelope is complete so corrections can be made.
- Perform exhaust duct and shaft leakage testing. Use Duct Blasters to perform this testing.
- Perform air balancing early during construction when HVAC is first energized and use blower door testing to provide data for HVAC air balancing. Keep in mind that failures can occur due to unbalanced HVAC system during construction activity.
This case study is a classic example of what can happen when efforts to achieve greater energy efficiency and air barrier tightness are decided upon without working out details and/or determining if they are achievable. As the green building movement becomes more stringent, it is likely that codes such as the IgCC will be adopted by many more jurisdictions. This will require owners, designers, and contractors to become more familiar with the complexities of meeting stricter air barrier performance. It will also force them to understand the various and developing technologies used to meet those performances, and determine how to specify, construct, and test for such performance.
With over 35 years of experience, Richard S. Scott is an expert in the areas of architecture, interior design, and building forensics, with a focus on moisture-related building problems. He is certified by both the American Institute of Architects/AIA Florida and the National Council of Architectural Registration Boards (NCARB). He has published over 30 articles, and has lectured or presented at nearly 40 seminars or events. Mr. Scott has developed various training courses, including a 16-hour IAQ training course for NASA and an 8-hour water intrusion prevention training course for the Naval Facilities Engineering Command (NAVFAC). He can be reached at email@example.com.