Colorado Real Estate Journal - May 4, 2016
Urban infill development in Colorado is hot right now. How hot? It has its own blog: www.denverinfill.com/blog. So, developers who tackle these projects clearly have their finger firmly on the pulse of the market, along with ample amounts of courage, vision and drive. But are these developers aware of the hidden challenges that can create substantial cost overruns? In this two-part series, experts will share how to avoid some of these obstacles and explain how proper planning with the right team can save you time, money and headaches. In first part, we look at the challenges of below grade construction and what to look for when your property is surrounded by existing structures. When Parking Goes Down, Challenges Go Up It’s no secret that land is a limited resource in popular urban locations. That’s why infill projects often involve below-grade construction for parking or leasable floor area. However, there has been an increasing trend toward construction of above grade parking structures to avoid the significant costs of excavation, shoring and, more recently, groundwater treatment. “Conventional soldier beams and lagging are still fairly common,” said Tom Soell, principal at JVA Consulting Engineers. “But, in some instances, neighboring properties and municipalities either won’t accommodate temporary easements to allow for tiebacks that cross the property line, or they’ll have special requirements within the right of way.” When alternative secant pier systems or other methods of shoring must be used that dimensionally protrude into your property, then proper planning can accommodate the additional thickness of the shoring into the final basement layout. It’s also important to note that certain shoring systems (secant piers, for instance) provide better protection from groundwater infiltration during construction. So if high groundwater is an issue, then the selection of a more robust shoring solution can offer significant savings. “With Studio Architecture’s guidance, we figured out how to add significant value to our recent infill project,” said Jeff Wingert, president and chief operating officer of W.W. Reynolds Cos. “They helped us achieve nearly 20 percent more leasable floor area in the building by creating a below-grade courtyard. And adjacent to (the courtyard) is more below-grade office space that gets ample daylight but doesn’t exceed the allowable floor area on the site. This was a huge bonus for us.” So, balancing below-grade construction costs against the added value of the leasable area needs to be weighed early in the conceptual design and entitlement phase. If you have the right team on board, it can uncover these unique opportunities. If not, you could be burying potential profit. What’s Next Door? Surrounding structures raise a number of concerns during urban infill construction. When building adjacent to an existing structure, meticulous planning must go into the selection and coordination of the new building’s foundation and below-grade shoring system. If not, the resulting challenges rapidly increase costs and can significantly delay construction. “It’s extremely valuable for the owner and contractor to invest in specialty services that monitor movement at the interface of adjacent properties,” said Soell. According to Aldo Sebben, design director and principal at Studio Architecture, historic buildings, and some contemporary existing structures, also may violate fire ratings associated with the existing walls along property lines. “On a recent project in Boulder, the building on our site was built adjacent to an existing historic structure and development plans required demolition of the contemporary building to make room for our new project,” said Sebben. “Since the neighboring building was over 100 years old, the temporary condition we uncovered on the other property made the neighbor’s exterior walls completely inadequate. That’s why it’s important to evaluate everything surrounding the property. If you don’t it could be a disaster.” How To Go With the Groundwater Flow If groundwater is going to impact the excavation for proposed below-grade structures, then it is important to evaluate whether you will treat groundwater permanently or build a watertight foundation. An early and detailed assessment of groundwater conditions, including groundwater monitoring to identify seasonal groundwater fluctuations, will help guide the design of shoring and foundation systems. “Within the last 10 years, Colorado has adopted new EPA standards on the discharge of groundwater into the storm sewer system,” said Soell. “When projects encounter groundwater during construction, and testing identifies the presence of excessive amounts of naturally occurring metals, the groundwater must be treated prior to discharge into the public sewer system. There’s just no getting around this incredibly costly issue.” According to Sebben, permanent groundwater treatment is necessary if a traditional perimeter drain and/or under slab drainage system is used prior to discharging the water. “Often, a small environmental plant must be built into the project at significant cost depending on the depth of the structure, the flow rate of the groundwater present and the extent of treatment required,” said Sebben. “Not only that, but with the addition of a permanent water treatment system, the owner has to absorb the system’s annual operating costs for the life of the building. On a recent project, evaluation of both options with the GC revealed that by raising the building slightly and building a watertight ‘bathtub’ we could eliminate the need for permanent groundwater treatment.” According to Sebben, this “bathtub” approach was used on our firm’s 17Walnut project with Element Properties and it eliminated the permanent groundwater treatment system. However, the basement walls and foundation had to be sized to resist higher hydrostatic loads and counteract buoyancy forces on the building. “This more robust solution can also be accomplished with a structural slab isolated from the soil and supported on drilled piers socketed into the bedrock,” added Sebben. “There are obviously significant construction costs associated with the ‘bathtub’ approach,” said Soell. “But this option eliminates any long-term operational costs associated with permanent groundwater treatment and discharge. Additional coordination with waterproofing specialists, as well as shoring subcontractors, is also critical when developing this type of system.” Proper Crane Planning Unlike suburban development, space utilization is a constant concern for urban developers. That’s why proper urban infill planning takes into account the placement of the construction crane within the building so that redesign of the structural and shoring systems, which add construction costs and time delays, will not be necessary. “We’ve learned over the years that some teams give little thought to the location of the crane until the project design is well advanced,” said Soell. “While it’s pretty easy to leave out an interior section of steel floor to accommodate a tower crane, temporary crane openings, on the other hand, greatly affect the design and cost of post-tensioned concrete slabs.” Additionally, there can be challenges associated with obtaining temporary airspace use agreements over adjacent properties. Failure to plan for and preferably limit temporary tower crane intrusion over your neighbors’ properties could delay construction and lead to additional preconstruction coordination and legal costs. “For a recent project in downtown Boulder, it was actually a question of geometry,” said John Wyatt, project manager for Wyatt Construction. “There was really no place to put a tower crane big enough to reach everything without hitting the nine story building next door.” According to Soell, if the project can’t accommodate a tower crane, then a crawler crane must be placed on grade adjacent to the line of shoring in a temporary easement within the right of way, as was the case with W.W. Reynolds’ Wencel Building. In this case, the temporary shoring must be designed for the crawler’s additional superimposed surcharge load. And failure to do so could result in even more costs to reinforce the shoring system during construction, or even worse, it could cause shoring damage and even failure. In the conclusion of this twopart article, we will look at challenges with site utilities and the ever-evolving energy-efficiency code requirements facing urban infill developments.