By Joshua Bowditch

Hub50House: Reflective Silvery Window Walls

There are several options that architects have for designing the exterior of a building, but perhaps the most efficient in regards to sustainability is with expansive glass systems such as the ES-W725 used at Hub50House. Overall, the design features a general rhythm of integral aluminum vertical and slab covers simultaneously with randomization of recesses or voids and architectural color scheme. The architectural glass-framing supplier ES has product capabilities for practically any climate and design application. In the temperate climate of the northeast United States, versatility to the changing seasons involves minimizing conductive heat loss in the wintertime, minimizing solar heat gain in the summertime, and allowing for opening up to the outside during times of mild weather. Along with the ES-W725 system are integrated ES-P7531 operable windows and ES-45T swing doors.

Sustainability with ES

Sustainability in the building industry involves the building materials, specifically raw materials, supply chain, and characteristics of the end product. ES is resourceful in procuring basic materials and is unique because it is part of a vertically integrated conglomerate which handles the precursory production stages of aluminum extrusion and glass processing. The implications are streamlining the supply chain and maximizing production efficiency, which correlate to cost savings and overall sustainability.

The Window Wall System

The ES-W725 is a highly efficient window wall system because it has the capacity for large spans of glass, and also because it is preglazed, also known as unitized1. This means the glass is structurally and hermetically sealed (unitized) to its aluminum frame at the factory as opposed to on-site, so that the sealant is applied and cured in a controlled environment, where there is no variation of temperature and humidity, and no exposure to airborne contaminants2. The silicone sealant Dow Corning 983 is used for structurally bonding the glass to the aluminum frame at the interior side1. Dow Corning 983 is a two-part sealant3; two-part sealants chemically cure within a few hours after mixing2. The size and weight of the dispensing pump required for applying two-part sealants makes field applications impractical2. At the exterior side of joints, Dow Corning 791 silicone sealant is used as a weatherproofing seal1. Silicone sealants are chemically stable and extremely durable with excellent resistance to weathering and aging4. The advantages of a preglazed unitized system include quality control of assembly, exterior side hermetically sealed, and expedited installation. The framing system also has a thermal break to minimize conductive heat transfer. An isobar is used to thermally isolate exterior and interior aluminum components, without compromising the strength of aluminum5.

High-Quality Extrusions

The material of the extrusions for the ES-W725 is 6063-T6 aluminum alloy or 6005-T5 aluminum alloy, depending on the component1. Aluminum is lightweight, high-strength, and reflective6, and these aluminum alloys have excellent extrudability7. The exterior aluminum alloy finish is Duranar® in accordance with the PPG Certified Applicator Program, in two different subtly contrasting colors, Sunstorm® Silver UC127728F and Sunstorm® Gray Mica UC128652F, according to the architectural color scheme. Duranar® is a fluoropolymer finish meeting AAMA 2605 performance standards8, which is the highest level of durability among exterior grade finishes for aluminum alloy extrusions6. In the coating process, the extrusions are pretreated and the coating is applied as electrostatic liquid spray to the extrusions, then cured at specified temperature. Aesthetically, fluoropolymer finishes are glossy.

High-Specifications Glass

The glass units are 1” nominal thickness, comprised of 1/4” clear glass with either SunGuard® AG 43 or Neutral 40 coating at the inward surface (surface #2), plus 1/2” insulating airspace filled with argon gas, plus 1/4” clear glass. SunGuard® AG 43 is a low-e coating, predominantly double microscopic layers of silver9, applied by magnetron sputter vacuum deposition (“MSVD”)10 and has a dynamic silver color tone when viewed from the exterior9. SunGuard® Neutral 40 is a low-e coating with neutral gray to silver reflective exterior appearance11, resulting in a subtle contrast with the SunGuard® AG 43. The glass is conveyed through a coating machine having a series of low pressure vacuum chambers where the microscopic layers are applied in sequence. The resulting glass is spectrally selective, providing high solar heat control while allowing high visible light transmittance. Argon gas is invisible and nontoxic, having lower thermal conductivity than air, used in combination with a low-e coating for optimal thermal performance.

Architectural Stewardship

Aesthetically interesting as Hub50House may be, these aspects 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”.
This article of Architectural Stewardship was sponsored by ES.

1 ES-W725 Technical Datasheet. 2016. Energía Solar (ESWindows).
2 Takish, 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.
3 Dow Corning Americas Technical Manual. 2002. Dow Corning Corporation.
4 Beall, C. 1999. Thermal and Moisture Protection Manual. McGraw-Hill.
5 Company Brochure. 2015. Alutions (Tecnoglass).
6 Aluminum Extrusion Manual, 4th edition. 2014. Aluminum Extruders Council.
7 Davis, J. R. 2001. Aluminum and Aluminum Alloys. In: Alloying: Understanding the Basics.
8 Architectural Liquid Coatings Color Guide. 2018. PPG Industries, Inc.
9 Sunguard® AG 43. 2021. Guardian Glass, LLC.
10 Expert Series: Energy Performance and Low-E Coatings. 2021. Guardian Glass, LLC.
11 Sunguard® Neutral 40. 2023. Guardian Glass, LLC.