Having It All: Achieving Performance and Aesthetics with Multi-Panel Door Systems

While contemporary design’s use of glass makes a beautiful, welcome, and modern space, it also places heavy performance demands on the windows and doors. As a greater percentage of wall space is occupied by glass, the insulative and performance properties of that glass and frame need to be increased to avoid placing an energy burden on the home or building. Besides impacting indoor heating and cooling loads, glass also controls the amount of natural daylight allowed into the home. The entire door system must also be graded 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. Understanding necessary certifications for door performance means confidence that a multi-panel system will not only look beautiful but will perform beautifully over the life of the building.

Energy Efficiency and Performance Codes Governing Windows and Doors

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 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.

Typical high-performance doors have U-factors of 0.32 or less and 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 North American Fenestration Standard/Specification (NAFS-08).

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 multi-panel doors, with air infiltration testing via ASTM E-283 criteria.

The structural integrity of a multi-panel door system ensures that it will perform correctly over its lifetime. High structural integrity in door units will 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 as multi-panel systems, with the results directly dependent on the size of the panels.

For commercial applications, AAMA publishes the primary standard for commercial windows and doors in AAMA/WDMA/CSA 101/I.S.2/A440-08: North American Fenestration Standard/Specification for windows, doors, and skylights. This standard defines four 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 for 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 psf, 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.

Special Circumstances: Approved Impact Systems

Approved impact multi-panel door systems refer to those systems certified to meet a hurricane/impact rating. Impact-rated systems generally incorporate additional hardware for maximum structural performance, laminated impact-resistant glass, and optimal weather seals for water resistance.

Approved impact systems must meet or exceed the impact testing protocols in compliance with Miami Dade County and obtained Notice of Acceptance (NOA) approval for use in high-velocity hurricane zones (HVHZ) and other wind-borne debris areas:

• Large missile impact
• Uniform static air pressure loading
• Cyclic wind pressure loading
• Water infiltration and resistance
• Forced entry

Manufacturer Testing and Certification

Manufacturers themselves can also gain certification. The National Accreditation & Management Institute (NAMI) has established product testing and quality assurance validation programs. NAMI certifications offer global certification and quality assurance designations. They specialize in fenestration and building envelope products, which include, but are not limited to, windows, doors, and glazing wall systems.

Checklist: Product Testing and Certification

The best manufacturers have multi-panel systems that are not only visually appealing but also are built to perform, even in the most severe climates and regions. Door systems should be developed, designed, tested, and engineered for optimal thermal performance, structural integrity, strength, and protection against the elements.

If a manufacturer is deficient in any of these areas, testing will reveal that inadequacy.

• Thermal performance and energy efficiency: When comparing performance between different manufactured systems, it is advisable to always look for products that have U-factors determined in accordance with NFRC 100. Manufacturers who participate in the NFRC Certification Program have their products listed in the NFRC Certified Products Directory, available online at www.nfrc.org. Each NFRC-tested unit is additionally shipped with a standard label identifying the key elements of performance: U-factor, SHGC, VT, and AL.
• Air, water, and structural performance: Testing is a vital tool in design philosophy and should be applied to every component multi-panel door systems. Doors should be independently tested, with performance results third-party certified.

Recommended testing includes AAMA, ASTM, and DP ratings.

Photo courtesy of LaCantina Doors

This home blends traditional Northeast Cape Code/Nantucket style with contemporary California craftsman architecture. Multiple Folding systems add modernity to create an open, airy environment. The architect for this project was Materia LLC.