ENHANCING PERFORMANCE

The expansive use of glass makes any home a beautiful, welcoming, and modern space. It also places heavy performance demands on that glass and the surrounding frames. As a greater percentage of wall space is occupied by windows and doors in smaller homes, the insulative and performance properties of those products need to be increased, to avoid placing an energy burden on the building. The entire system must also be evaluated on its ability to prevent air leakage, how it will interact with weather events, and how it will stand up to the wear and tear of daily use. This is where energy and performance codes become invaluable. Understanding the certifications for door performance means selecting with confidence a movable glass system that will not only look beautiful but will perform beautifully over the life of the building.

In tandem with the improved health metrics that movable glass panel door systems can provide, enhancements in manufacturing and technology have increased efficiency. Today, these systems can occupy a greater area in the building envelope without compromising overall performance.

Private Residence – Los Angeles, California

Photo: Thomas J. Story; © 2024 Sunset Publishing Corporation

Multiple panel doors transformed an underused pool house into a welcoming hub that can play host to multiple activities.

Before it was entirely reimagined, this underutilized poolside wing of a traditional Los Angeles home had good bones, but little in the way of light and one too many walls. The idea was to transform this formerly dark warren into an inviting, multipurpose space. The principles applied during the renovation were tried and true: increase the volume of the space and let in as much natural light as possible. To accomplish this, a wall was removed, natural wood surfaces were simply and lightly stained, and abundant sky lights were added. For full, multifunctional impact, floor-to-ceiling folding doors were installed on two sides. The result is a luminous light box promoting conversation, collaboration, and casual entertaining by the pool.

With rolling hardware and robust panel-and-frame designs, the folding door systems selected provide smooth and effortless operation and have the ability to span any size opening. Clean, minimalist lines and cladding in a subdued and handsome bronze anodized finish allows the doors to meld seamlessly with the low-slung structure. Sleek hardware allows for effortless unlocking of the doors and a solid grip when operating the system.

The aluminum exterior cladding and wood interior offers durability, thermal efficiency, and aesthetic versatility. The vertical-grain Douglas fir wood serves as a neutral backdrop that allows the room’s curated collection of vintage furniture and objets d’art to stand out and serves as a more organic and natural framing for the landscaping and pool outside.

Thermal Performance

Classifying and labeling the real thermal performance of door and window systems is the focus of The National Fenestration Rating Council (NFRC), a not-for-profit trade association. NFRC 100 “Procedures for Determining Fenestration Product U-factors” is the accepted standard for rating windows, doors, and skylights for U-factor.

A U-factor is typically rated between 0.20 and 1.20. This standard establishes standardized environmental conditions, product sizes, and testing requirements, so that architects and others can make informed choices fairly and accurately by comparing the performance of different products.

NFRC testing also looks at other overall performance characteristics, including the solar heat gain coefficient (SHGC), which measures how much solar energy passes through a particular glazing, creating heat gains inside a building. A SHGC is expressed as a number between 0 and 1. In areas where heat gains are a concern, coatings are applied to the glass to allow less transference.

NFRC testing additionally assigns a value to the visible light transmittance (VT). Values are between 0 and 1. VT determines the effective light available for daylighting, helping gauge potential offset of electricity costs for lighting a building’s interiors.

U-factor, SHGC, VT, and air leakage (AL) are all disclosed on an NFRC label for an individual product. The lower the U-factor, the better the insulation level of the unit, meaning less loss of heat to the outside. A low SHGC number means more solar energy will be blocked, eliminating passive heat gain from outside into the building. The higher the VT, the more natural light is transmitted through a product.

A typical high-performance door will have a U-factor of 0.32 or less and an SHGC of 0.30 or less, depending on climate zone.

Air, Water, and Structural Performance

In addition to thermal performance, codes and standards, including those of the NFRC, have increasingly recognized air leakage (AL) as a very significant factor in fenestration performance. Today’s window and door products must meet minimum standards for air infiltration, and be tested, certified, and labeled for this performance. The total system must be able to withstand wind pressures associated with its geographic location, and air leakage must be controlled not only for energy performance but also for occupant comfort and long-term durability of the fenestration system. NFRC expresses AL as a number ranging between 0.1 and 0.3. A higher AL means greater air infiltration over the life of the product. The most suitable AL rating for an energy-efficient building will be at or near 0.1.

Better manufacturers may also offer testing that reaches beyond air infiltration and measures air exfiltration. Certain product categories may require exfiltration testing and certification, per the NAFS-08, or North American Fenestration Standard/Specification.

Each potential system should have an American Architectural Manufacturers Association (AAMA) Product Performance Class as well as a minimum Design Pressure (DP) rating. ASTM E-547 tests water penetration of movable glass panel door systems, with air infiltration testing via ASTM E-283 criteria.

The structural integrity of a multiple-panel door system ensures that it will perform correctly over its lifetime. High structural integrity in door units allows the system to maintain proper fit and operation of the products under conditions of wind, rain, and other weather stresses. Structural Load Deflection testing is typically measured under ASTM E-330 and should be reported by the manufacturer. This test is used for standard doors as well movable glass panel door systems, with the results directly dependent on the size of the panels.

For commercial applications, or residential applications seeking commercial ratings, AAMA publishes the primary standard for commercial windows and doors in its document AAMA/WDMA/CSA 101/I.S.2/A440-08, “North American Fenestration Standard (NAFS)/Specification for windows, doors, and skylights.” This standard defines four (4) different Product Performance Classes: R, LC, CW, and AW. It also identifies the minimum Performance Grade (PG) that is required to satisfy the criteria of each class. The defining criteria is the minimum design pressure (DP) that a unit must resist such that class R must withstand 15 pounds per square foot (psf) of pressure, class LC 25 psf, class CW 30 psf, and class AW 40 psf.

In addition, each class must meet minimum water resistance test pressures ranging from 2.9 psf for Class R, 3.75 for Class LC, 4.50 for Class CW, and 8.0 for Class AW. ASTM E-547 tests water penetration. The specified sill configuration routinely has a direct influence on the results. The ability of the door as an entire system to either seal water out completely or to manage water, so that any water penetrating the system drains away, is analyzed under ASTM E-547. As an example, multi-slide glass doors have been tested using these ratings and standards and have been found to meet overall DP ratings of up to 45 with additional structural up to 90 psf and no water leakage at up to 6.8 psf.

Impact probability also is classified as high, moderate, or low. Doors subject to high impact are often the very same doors with a high frequency of use, but not always. Referring to ANSI/SDI A250.8 may be helpful in guiding selection.

Photo: Thomas J. Story; © 2024 Sunset Publishing Corporation

It is a misconception that doors cannot be efficient. Modern designs have evolved to incorporate advanced materials and technology to enhance energy efficiency. Features like low-emissivity (low-E) glass, multiple panes, and enhanced insulation have become standard, ensuring that today's patio doors have the highest levels of style and performance.

Enriching Sustainability

Movable glass panel door systems can enhance efficiency by selecting energy-efficient glass, glazing features, and thermally improved frames. Leading manufacturers offer doors with dual-paned tempered glass as a standard, creating an insulating barrier between the inside and out. Advanced low-e glass options are available to help reduce cooling costs in the summer and heating costs in the winter.

Photo courtesy of LaCantina

Innovations in multiple panel doors ensure reliability and performance even in challenging weather conditions.