IA Q vs. Energy: Myth vs. Reality
Some designers think that the way to achieve good indoor air quality means that energy performance has to be compromised. This is commonly referred to as the Energy IAQ tradeoff and the reality is that it is a misperception. It seems to be born of the mistaken thought that the only effective strategy is to increase the use of mechanical ventilation. But the reality is that a welldesigned building can have both good IAQ and good energy performance.

As we have been seeing, there are many building enclosure design strategies to address IAQ that don’t compromise energy efficiency, in fact they will enhance it. Control and reduction of pollutants at the source can be accomplished by specifying low-emitting materials in the enclosure as well as the interior. The enclosure can be designed and constructed tightly to restrict air flow through it particularly in variable pressure conditions. The HVAC system can be designed to integrate with the tighter enclosure and work more efficiently. The integrated system will then go a long way toward more accurately controlling outside air and air changes per hour.

When it comes to creating continuous barriers that is important for air and vapor but also for thermal barriers. Continuous insulation installed on the outside of structural and other elements helps cover over anything that would otherwise be a “thermal bridge.” In many cases, the insulation may also have air and vapor barrier properties meaning that one product can perform multiple functions very efficiently. Regardless of the material used, however, there are several places in the building enclosure that are critical and require attention to the details. The first is any area of transition where sections of the same materials meet. The junction points and/or seams are prone to leak if not joined together properly. The second area is terminations where two different materials start and stop. Obviously if there are gaps or spaces between these two materials because of framing or differences between the materials then leakage is likely. The third critical area is repetitive features. If a feature is detailed wrong and applies to multiple locations, then each of those locations will have issues.

Paying attention to all of these things in the building enclosure details will create effective systems that are indeed energy efficient and address IAQ at the same time.

Timing of Design Decisions
Anyone managing a project understands the importance of addressing the timing of decision making. This is particularly true in the design of building enclosure systems. Since there are an abundance of choices, it is wise to address the criteria and selection of those systems early on. By starting out with a correctly conceived set of enclosure systems, it is easier to stay on track through a successful completion. Discovering later on in the process that changes are needed for the enclosure to work and perform properly can create significant impacts to the design team, the construction team, or to the ultimate health of the occupants. Therefore, working out the details in the schematic or design development phases of a project means there will likely be minimal cost impact since making adjustments are fairly simple early in the design process. Waiting until construction drawings and specifications are being prepared might mean that the design firm needs to re-design and re-draw portions of the project with potential higher cost impacts. This is especially true if the revised design requires re-bidding or delays the project. Discovering a change needs to be made during construction usually means that a change order is required for re-doing something that may already have been built. That can have professional liability costs for the design team and cause further scheduling delays for the owner. Finally, if a problem is discovered during occupancy, this will likely be the most costly to revise and correct. (See Case Study). The implications of a poorly designed and constructed building enclosure could include loss of use of the building during repairs, creating a remedy that is limited due to inaccessible assembly locations, and damage not only to the building, but to the reputations of all involved.

One activity in particular needs special attention, namely the increasingly common Value Engineering step of a project. A substitution or change in the building enclosure can have some dramatic ripple effects since they affect so many other areas as we have seen. The impacts of any change need to be evaluated based on what it does to each of the control layers individually and collectively as a coordinated assembly. It also needs to be assessed based on the impacts it may have on the HVAC system. Given the importance of the enclosure and the potential building and health impacts, the final determination for making any such changes should rest with the architect or other licensed professional that designed the building enclosure systems.