The Evolution of Aluminum Framing Systems

by Jonathan McGaha | October 31, 2013 12:00 am

Do you remember when the term “thermally efficient” never crossed your mind when talking about storefronts and entrances? With recent modifications to energy codes and with emphasis on decreasing energy costs, aluminum framing systems have undergone an evolution toward increased thermal efficiency. This evolution has even touched basic commodity products like storefront and entrances.

 

Historically, storefront systems have been designed for basic commercial applications usually involving first floor openings with entrances. These systems were mostly non-thermal with 0.25-inch glazing, meaning that the main framing members consisted of a single extrusion not separated by any type of thermal break. It was a fairly inexpensive way to close in the lower floors of a building. But with increasing concern about the thermal efficiency of buildings and the energy output required to heat and cool them, storefront systems evolved from non-thermal systems with 0.25-inch glazing to more complex products. These involve standard and high-performance 1-inch glazing, single and dual poured and debridged pockets, thermoplastic snap-on glazing clips and mechanically crimped struts to separate the exterior exposed frame from the interior.

 

The old 1.75- by 4.5-inch storefront systems for 0.25-inch glazing had estimated U-factors in the 1.00 range. Modern 2- by 4.5-inch systems with 1-inch low-E glazing and dual poured and debridged thermal pockets can achieve U-factors below 0.30 with high-performance glass. U-factors based on NFRC 102 procedures for determining thermal transmittance.

 

Current trends for these modern storefronts are not only indicating more use of thermal break technology, but also show increases in the interior metal area to improve Condensation Resistance Factor (CRF) values. This can add one or more points to the CRF, depending on the glass configuration.

 

Basic entrance systems have not changed much in form or function during the past few decades. There have been some cosmetic and hardware improvements that have updated the appearance of the aluminum entrance door, but it is still a typical narrow, medium or wide stile door usually 1.75 inches thick and offering either 0.25-inch or 1-inch glazing.

 

Regarding thermal performance, doors have never traditionally been a major contributor to the thermal efficiency of a commercial building. Architects and building owners have tried to offset performance issues by adding vestibules and dual pane glazing, but these options are not always practical or economical. Simple solutions were devised to help improve the thermal performance of entrance systems. One of these solutions was to clad the interior of the door with special extrusions that basically snapped onto thermoplastic clips on the main door stiles and rails. This offered a small thermal break that helped reduce the formation of condensation.

 

The advent of “strutted” framing systems introduced polymer, thermal break materials that are crimped between interior and exterior framing members. With these thermal struts, entrance systems’ manufacturers realized more design flexibility that previously was not possible with traditional thermal break technology. Strutted doors started appearing on the market, which provided improved thermal performance. It also added the benefit of two-color capability, allowing different colors and finishes on the exterior and interior, without the cumbersome aforementioned cladding.

 

Taking a cue from European designers, some manufacturers designed ultra high-performance entrance systems employing struts, dual seals, thermally broken thresholds and options for triple glazing in a door thicker than the standard 1.75-inch. These high-performance doors can produce U-factors and CRF numbers similar to some storefront and curtainwall systems, depending on the glass used. Combined with proper building design, newer entrance systems like these can dramatically improve a building’s overall thermal efficiency and the occupants’ comfort.

 

Thermal efficiency requirements not only affect new construction, but also older buildings’ renovation and upgrades. As energy costs rise, building owners are finding ways to improve their building’s overall performance. Retrofitting has gained in popularity for this reason. The challenge going forward is to increase thermal performance in retrofit applications using existing entrance systems’ frames, when feasible, and minimizing disruption to building occupants.

 

The evolution of entrances and storefront to more thermally efficient systems has only just begun. With new materials and processes being introduced to the market place, the building team members and manufacturers are helping reduce energy costs and provide a more comfortable work environment, both for new construction and retrofit applications.

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Greg Hall is the product development engineer III at Tubelite Inc., Walker, Mich. To learn more, visit
www.tubeliteinc.com[1].

Source URL: https://www.metalarchitecture.com/articles/the-evolution-of-aluminum-framing-systems/

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