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Science Behind It The Extension of a Building Envelope By Heather Paschal, AIA, LEED AP, Assoc. at Henry Co. T raditionally, a defned building envelope is limited in scope only by the confned space that is created using a foundation, exterior walls, and roof. By this description, building functionality does not consider outdoor space, adjacent structures, environmental impacts, or how occupants engage the building envelope within a city context. As building codes change, it is no longer logical to be bound by the predeterminations of a conventional building envelope defnition. Roofs are now areas of vegetative space and congregation instead of locations to hide or store mechanical equipment. Architectural design takes into consideration how best to approach a structure when people are using public transportation and even recognizes the importance of air quality with designated smoking areas. By extending the building envelope into the community, it becomes possible to assess the functionality of a city as a whole and to ofer a new way of analyzing efciency and life cycle costs. Te most recent enforced changes to building envelopes are reduction of heat island efect and storm water runof. Tere are a number of ways to achieve minimum code standards. However, communities are starting to see innovative ways of not only exceeding these minimum requirements but also creating a better quality of life for city occupants. One example of extending the building envelope is the Klyde Warren Deck Park located in Dallas, Texas. Pushing the Envelope Like many cities, Dallas was burdened by a highway separation, preventing continuity and growth of adjacent thriving areas. Although Dallas's known Downtown, Uptown, and the Arts District developments were successful, there were no inviting pedestrian methods of connection due to separation created by the Woodall Rogers Freeway. Not only was the city divided, but the amount of non-pervious surfaces contributing to storm water runof and heat island efect was troublesome. In an attempt to further unite Dallas and create a more energy-efcient city, a 5.2-acre (21,044 m²) deck park was proposed and approved for installation over the recessed eight-lane Woodall Rogers Freeway. By approving the installation of a large-scale vegetated and pervious surface intended for occupant use, the city would not only be uniting the disconnected developments but also decreasing storm water runof and heat island efect on a massive scale. To safely accomplish the intense project goals, structural integrity and longevity of the park would be crucial, requiring convergence of bridge design, building envelope waterproofing, and vegetative roofing ingenuity. The proposed deck park was designed and constructed out of more than 300 concrete beams with concrete slabs spanning the width of the freeway. Trenches were strategically calculated to simulate planter boxes, allowing trees to grow to projected necessary sizes. To keep the deck as light as possible, a combination of Geofoam and engineered soil was selected. It was also pertinent to rely heavily on traditional methods of building envelope waterproofing for ensuring performance and durability of the project. Ultimately, Henry Company Elasto-Seal 790-11EV Hot Rubberized Asphalt assembly was chosen to waterproof the park deck, partly to provide a water tight building envelope coating and contain few assembly limitations. Furthermore, hot rubberized asphalt warranties can easily last up to 20 years, even when applied onto a completely flat substrate, thereby meeting the large scale project requirements. Due to the fact that hot rubberized asphalt was installed on the Klyde Warren Park to solve a waterproofng conundrum, which is traditionally considered a building envelope concern, there is cause to question how exactly the project should be characterized. Te development is a bridge, a park, and a series of designed spaces, and it includes an operable air conditioned building. Consequently, it does not fully ft into any one category. Perhaps instead there should be only one category in quantifying a project by how efciently it contributes to overall air quality, durability, and proper drainage, as well as how it ofers protection of the components or occupants from the weather. Tis way, design and construction professionals are challenged to alter the way an efcient envelope is imagined indefnitely. Building Envelope Innovation Klyde Warren Park ofcially opened in October 2012. Te deck park may have never become a reality without the understanding of a productive building envelope and the ability to successfully combine bridge design, waterproofng, and vegetative roofng into the development of a unique project. Te addition of new structures in the Dallas area will undoubtedly take a lesson from the design experience pushing the boundaries of what a building really is. Te future of construction is no longer just about the building envelope; it's about a city envelope. CP COATINGSPRO JANUARY 2014 91