Factors to consider when redesigning podium decks

Completed podium restoration at 30 Greenfield Avenue.
Completed podium restoration at 30 Greenfield Avenue.

Appropriate waterproofing system

The design and detailing of appropriate moisture protection is a challenge unique to each site and structure, with consideration required for service life, overburden types, and environmental factors. Hydrostatic pressure is handled by designing the waterproofing assembly to be drained with the drainage board and area drains (either existing or new ones). The whole design process focuses on creating an environment without hydrostatic water pressure and effective drainage systems in place. Informed selection requires knowledge and understanding of available products and their performance characteristics. Liquid-applied asphaltic waterproofing systems have a squeegee-applied hot rubberized asphalt waterproofing membrane overlain with a protection and drainage layer. In two-ply systems, the hot rubberized asphalt waterproofing is reinforced with inter-ply fabric reinforcing sheets.

Liquid-applied hot rubberized asphalt systems have useful installation characteristics—particularly, they can be easily installed at changes in elevation, over concrete curbs, and up perimeter walls. They also allow for simple tie-in details at drains and other termination points. When installed with appropriate protection courses, overburden can be readily installed with little risk of damage. The waterproofing work can also be completed in phases, with tie-in to previously installed waterproofing completed with a simple lap that provides a watertight seam.

Plan for landscaping finishes

Depending on the podium deck use, size, and existing conditions, the design may require input from various team members. It is important to share design ideas and concepts with the stakeholders early in the design process to set an achievable target that has anticipated costs in line with available budgets. It is important to design to an achievable goal to prevent rework or future surprises.

Engineering firms experienced with podium deck rehabilitation work along with combined envelope and structural engineering expertise are valuable allies and can assist in setting and achieving reasonable rehabilitation targets to maintain the podium deck and meet functional and esthetic goals. The engineer reviews proposed changes and assesses their impact on the structure, including assuring applied loads remain within design capacity, or are accommodated for with structural strengthening. Other professionals may not realize they are exceeding allowable loads by changing overburden materials and depths, or by installation of structures, statues, or other elements.

An arborist should be consulted when replacing or adding new trees to a podium deck—whether required in a particular jurisdiction or not—to assess viability and growing conditions. Trees require minimum depths of soil, and specific soil and climatic conditions to grow, survive, and thrive. The engineer can cross-reference arborist recommendations to ensure the structure can safely support the weight of the growing medium and the mature tree, which will exceed the installed weight.

Older podium deck paths of travel may not meet current code requirements, accessibility recommendations, or public expectations. The design should accommodate for safe and functional walkways and travel paths through the site, which should be constructed with non-slip and durable surfaces with handrails and other appropriate aids, where required. Use high contrasting materials at stairs and tactile warning plates where required by current accessibility guidelines or codes. This is an opportunity to create a safe and enjoyable space for everyone, and to correct obvious design issues building occupants may have discovered over the years.

Thermal performance should be considered where the below-grade areas are heated or can benefit from better heat retention. Depending on the construction and age of the building, rigid insulation may require replacement or may be warranted as an addition to the podium deck overburden. Understanding the original design and current site needs will inform placement of insulation, but, as a minimum, it is important to maintain at least the same level of thermal performance.

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