FTI's Advocacy Committee Submits LEED v4 Proposal to Improve Facade Performance and Occupant Comfort

FiDi NYC, One World Trade

LEED has become the international standard for the design, construction, and operation of high-performance structures. LEED v4 is designed to up the ante with a more flexible, performance-based approach that calls for measurable results throughout a building's life cycle – allowing for a more streamlined user experience and more goal-oriented credits.

FTI's newly formed Advocacy Committee recently submitted three proposals in response to the USGBC's new LEED v4 announcement including recommendations to add a credit for assessing condensation resistance, a bundling option that ensures appropriate envelope performance, and improved delivery of thermal comfort near facades.

Credit for Assessing Condensation Resistance

Indoor air quality has been established as a key requirement for occupant health, well-being, and productivity. Condensation as a result of poor performing windows and thermal bridging across facade attachments and interfaces can cause condensation which can create breeding grounds for mold and bacteria on walls, carpets, ceiling tiles, etc. and negatively impact indoor air quality. Though some countries have already implemented building code requirements, energy codes and standards do not effectively address these issues and allow designers to ignore major thermal bridges in the envelope. As a result, energy models underestimate building energy use and can result in an under-performing building. We proposed a pilot credit in the IEQ credit area to reward project teams who make their best efforts to design against condensation occurring inside the wall and on the fenestration.

Ensuring Appropriate Envelope Performance

Currently, design teams can specify a relatively poor performing envelope, and less than the local prescriptive code might allow, by trading off with a high performing HVAC, lighting and other internal systems in the Energy and Atmosphere credit area. This trade-off is happening throughout the US and results in a poor thermally performing envelope which will likely result in an uncomfortable perimeter zone.

The easiest solution to this problem would be to require that the fenestration and wall assemblies meet the minimum prescriptive requirements for U-factor and solar heat gain coefficient. However, this removes the flexibility to design to a single performance metric – building energy – rather than a range of performance metrics including occupant comfort. To achieve whole-building energy performance targets without compromising envelope performance and occupant comfort, we proposed a bundled incentive to improve both the energy performance of the building and the comfort next to the facade.

Improve Delivery of Thermal Comfort Near Facades

The facade can significantly impact the mean radiant temperature of the perimeter space of a building due to long-wavelength radiation from hot or cold glass and metal window surfaces and from short-wavelength direct solar impingement through the glass. Thermal comfort next to a facade remains a significant problem because of uneven radiant temperatures, convective drafts next to cold windows and direct solar impingement coupled with the challenges with managing this through HVAC design. To ensure that projects are adequately evaluating and addressing these issues, we recommend that documentation be provided to demonstrate robust compliance and that appropriate analysis has been done, especially around the building perimeter.

To read the proposals in full, you can download the compiled PDF.

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