AGG - USG AddOn - Jan 2006 - Spring - Condo Construction Technical Issues

AGG

Winter 2006

Condo Construction Technical Issues

by Mike Logan and Barry Gaston

The overall development process for a condominium project depends largely on the type and location of the project. In new construction, a multi-unit, low- to mid-rise development can be completed in as little as 12 months, while a high-rise, luxury building can take as much as 42 months. In a conversion from an office or warehouse building, the schedule can vary and is driven by the time required for demolition and reconstruction of the existing building.

Several technical issues have to be addressed, and they vary both by project type and geographical location. Local codes vary from hurricane debris impact codes to requirements for operable windows to special energy requirements. The system types vary from punched windows with EIFS surrounds to custom curtainwall. The factors vary greatly based on the economics of the project and the regional building trade traditions.

Curtainwall Versus Window Wall

The overall building frame, geometry, floor heights and performance requirements will usually dictate the proper system to be used for the exterior wall. The statement that a window wall is always less costly than a curtainwall may not be true in all cases. If performance requirements show that a window wall needs internal steel reinforcing and slab edge covers and a unitized curtainwall does not, the added cost of steel, shop fabrication and field installation may prove curtainwall to be more economical.

Components are the determining factor in wall cost. Sliding doors, operable windows, screens and balcony railings can add up to 20 percent to the overall cost of the wall. Balconies also create other concerns. Typically the doors onto balconies (both swing and sliding) have high thresholds in order to control water infiltration. These high thresholds become barriers from an ADA standpoint and require special consideration. Incorporation of a balcony railing system that is designed to mirror the exterior wall system has unique engineering requirements. The points where the balcony meets the exterior wall can present both aesthetic and performance issues, such as air, water and sound, that need to be solved.

There are three key technical areas that impact system selection. First is movement. Curtainwall inherently handles building movements better that window wall systems. Of course, there are exceptions to every rule, but the taller the building the more likely that curtainwall will be the solution.
Second is energy. New energy standards and codes along with the emphasis on sustainable design have encouraged the use of high-performance glazing systems. The uses of low-E coatings, laminated glass and factory assembled thermally-efficient units have become standard in new construction. The new energy requirements have resulted in a variety of standard framing systems designed to limit thermal transfer from the exterior to the interior of the building.

The third element, sound, is probably the least understood criteria. Due to the larger spans typically involved, curtainwall has a tendency to transmit sound from the outside into the occupied space. Because the wall is not in continuous contact with the floor slabs, sound from above and below tends to move around the floor slab edge. Window wall minimizes these issues, using the extended slab as a positive sound barrier.

Each project requires trade-offs between system types when addressing specific project needs. There is no single, optimum solution for all situations.

Mike Logan and Barry Gaston are the manager of the Midwest regional office and business development manager, respectively, for Heitmann & Associates Inc., a building enclosure consulting firm based in St. Louis with locations in New York, Chicago and Phoenix.