By Joshua Bowditch
Panelization of precast concrete panels in the shape of large casings around 2-story curtain wall openings architecturally describes Thousand & One in Tampa. This is an example of using architectural precast judiciously with expansive glass systems. Here the concept of prefabrication is taken a step further, with preglazed curtain wall segments being fastened to the architectural precast concrete at the precast facility. The architectural precast panels were made by STABIL Concrete Products and the modules were trucked to the project site. Lifted in place by crane, the modules were attached to the structural frame by embedded steel connections. From a construction standpoint, the advantages are simplification of the exterior wall assembly, consolidation of the construction process, and minimizing fallibilities of jobsite labor.
Architectural precast is distinguished by casting method and composition of the concrete. It is well-consolidated concrete with a low water/cement (w/c) ratio, instead of conventional self-consolidating concrete. These factors are made possible by casting the concrete at a controlled environment production facility. The distinctive aspect of precast concrete is impermeability, as it is impermeable to air infiltration and wind-driven rain1. During heavy rains, precast concrete may absorb some moisture at the surface, but the impermeability of precast concrete prevents moisture intrusion beyond a surficial extent, and it will dry out by evaporation1. The implications are controlling infiltration of moisture into the building envelope which is the goal in hot and humid climates, and resistance to weathering and efflorescence. Precast panels are unpainted and therefore are their inherent coloration, which here is standard white concrete.
Architectural precast is a superior form of concrete because of its impermeability, thermal mass, and simplification of the exterior wall assembly. The use of architectural precast gives higher value and more sustainable utilization to the constituent materials than conventional types of concrete. These constituent materials are of significant economic interest and environmental concern in the state of Florida. Mining of suitable-quality limestone results in irreversible loss of natural habitats and detrimental impacts to environmentally sensitive surroundings2. Portland cement production is very energy-intensive and a major source of industrial emissions resulting from thermal decomposition of raw materials and combustion of fuels3.
The term “curtain wall” refers to aluminum framing that supports the glass. The emphasis of curtain wall design is to allow for expansive glass panels with the capacity to withstand high wind pressures and impact of projectiles, and to have efficient closure at the joints to prevent intrusion of moisture into the building envelope. The curtain wall system used is the WTG-700 captured, by West Tampa Glass Company. It is a preglazed system, meaning the glass is sealed to its aluminum frame at the factory as opposed to on-site. With preglazed systems, the glazing (sealant) is applied and cured in a controlled environment, where there is no variation of temperature and humidity, and no exposure to airborne contaminants4. The structural sealant Dow Corning 983 is used at the glass to aluminum interface, at the interior side of the glass, and Dow Corning 795 is used as a weatherproofing seal at the exterior side of joints5. The advantages of a preglazed system are threefold: quality control of assembly, exterior side hermetically sealed to prevent moisture intrusion, and expedited installation. The exterior aluminum finish is Duranar® Bistro Bronze, a fluoropolymer finish meeting AAMA 2605 performance standards6, which is the highest level of durability among exterior grade finishes for aluminum extrusions7.
The high-performance glass units are 1-5/16” nominal thickness, comprised of three plies of 1/4” glass; specifically, one ply of 1/4” clear glass with Solarban® 70 low-E coating at the inward surface, plus 1/2” airspace, plus two plies of 1/4” clear glass with a laminate interlayer. The term “low-E” refers to reduced emissivity of heat from the glass surface. Solarban® 70 consists of three microscopic layers of silver applied by magnetic sputter vacuum deposition (“MSVD”), and has a color-neutral exterior appearance8. The use of expansive glass contributes many sustainable aspects to the project. Glass allows natural light which is not only a light source, but is also psychologically beneficial to the occupants. The glass, featuring advanced low-e coating technology, is spectrally selective, providing high solar heat control while allowing high visible light transmittance. Glass is produced efficiently from abundant and readily available silica sand. Glass is impermeable, which is an invaluable characteristic in the hot and humid climate.
Aesthetically interesting as Thousand & One Water Street may be, these aspects described would be generally unknown. It is publications like this one that can provide representation of these sustainability aspects through description and illustration. That would be the intent of “Architectural Stewardship”.
Special thanks to Roger Campla of West Tampa Glass Company for specifics on the curtain wall system.
1Architectural Precast Concrete Manual, Third Edition. 2007. Precast/Prestressed Concrete Institute
22009. Final Supplemental Environmental Impact Statement on Rock Mining in the Lake Belt Region of Miami-Dade County, Florida. U.S. Army Corps of Engineers (USACE)
3van Oss, H. G. 2015. Cement. Page 16.1-16.32. In: 2013 Minerals Yearbook. United States Geological Survey (USGS).
4Takish, M. S., M. H. Haugsby, C. M. Schmidt, and W. J. Schoenherr. 1989. Structural Silicone Sealant Curtain Walls: Field or Factory Glazing? In: Science and Technology of Glazing Systems, ASTM STP 1054, American Society for Testing and Materials, pages 58-65. C. J. Parise (ed.)
5Product Approval #12809.2 (WTG-700 System by West Tampa Glass Company).
6Architectural Liquid & Powder Coatings Color Guide. 2013. PPG Industries.
7Aluminum Extrusion Manual, 4th edition. 2014. Aluminum Extruders Council.
8Solarban® 70 Product Data Sheet. 2022. Vitro Architectural Glass.
About the Author: Josh Bowditch
As a native resident with architectural experience and environmental regard, Josh Bowditch is intent on publishing about sustainability in the architectural and building construction industry locally. From being in the architectural profession, Josh has an understanding of the processes involved. Is it possible to reconcile environmental considerations with development? The word sustainability has various connotations but indeed can be viewed in the context of stewardship.
