Multi-Slide Glass Doors  

Creating a visual connection between indoors and outdoors has long been a design goal in both commercial and residential buildings. Going beyond the visual and creating an actual physical connection between the two has often relied on a series of doors with interrupted access at the spaces between those doors. However, new product offerings using multiple sliding door panels that stack or store in wall pockets now make it possible to fully connect indoor and outdoor spaces, without the interruptions. When open, the indoor spaces extend outward to create an outdoor living experience with all the benefits of fresh air and daylight. When closed, attention to details and performance characteristics assure that the multi-slide doors provide the needed protection from the weather and climate conditions.

Designing for Open Spaces with Multi-Slide Glass Doors

Many building designs seek to capture outdoor spaces as part of the overall usable space related to a particular building. In commercial building designs, restaurants, office buildings, and apartments all can benefit when outdoor weather conditions make it more compelling to function outside rather than indoors. In residences, rooms that flow into patios, decks, or natural outdoor areas such as beaches or wooded areas, give residents a direct connection to those outdoor spaces. In all cases, it is the interaction between indoors and outdoors that becomes the key design focus—how to create the transition space or mechanism to allow the enjoyment of the outdoors but still access the functional needs of the indoor spaces.

Many 20th century architects worked with this concept of connecting indoors to outdoors but were limited by the technology and products of the time. The glass houses of Phillip Johnson and Mies van der Rohe created the celebrated visual connections but relied on conventional swinging doors to make the physical connection. Frank Lloyd Wright often used a series of double swinging french-style doors that opened out against the sides of a column or pier, making the whole assembly appear as a colonnade with the doors visually disappearing. All of this was contemporized into the mainstream home construction market through the use of sliding patio glass doors that typically provided one fixed and one movable sliding panel of framed glass at the same head height as other swinging doors.

Architects today who are looking to use this same design concept of connecting indoors and outdoors have more options and better choices than those who preceded us. In particular, designing with multi-panel sliding glass doors provides an opportunity to create a seamless connection between indoor and outdoor spaces while blending fully into the total building design. As a product, multi-slide glass doors are typically comprised of a number of individual sliding door panels that are guided on a head track above and ride on a floor sill below with bottom mounted rolling hardware. When open, they can either stack in one or more parking bays along the plane of the opening or recess into a pocket designed for that purpose. Similar to systems that use a series of panels that fold, the sliding operation also offers flexibility in terms of space requirements and configurations. Other notable features of sliding systems are discussed further as follows.

Typical Applications

Multi-slide glass doors are being used in a full range of building types and functional applications. Residential buildings are able to open up entire walls and connect main living areas with outdoor spaces. Multifamily developments use them to help create the feel and appeal of a larger living unit by extending to outdoor balcony and common spaces. Restaurant and retail buildings can cater to customers who prefer to relax in outdoor spaces while still being directly connected to the indoor facilities available. Resorts and hotels similarly can provide their guests with a convenient and inviting indoor/outdoor experience for individual rooms or for common lobby, restaurant, or function areas. Educational buildings that need to have the ability to expand a space to accommodate gatherings can use multi-slide glass doors that extend to adjacent outdoor areas. Offices that open to a central atrium or courtyard can use them to provide open access when desired or be closed off when needed. In short, their use is only limited by the imagination and creativity applied by the building designer.

Typical Sizes and Configurations

Multi-slide glass doors are generally used to create large openings in walls or to take the place of an exterior wall altogether. The size of the panels and the total door unit can vary and is usually custom fabricated to suit a particular building project. As a practical matter, the glass in an individual multi-slide panel is generally limited to 60 square feet in size with the caveat that the height is generally limited to 12 feet while the width is generally limited to 8 feet. The number of individual panels can vary to suit the overall opening size but there is generally a maximum of six panels that can be stacked up in each direction as a practical matter. Note that while these products are commonly used in door sizes, they can also be designed and used in shorter window sizes such that they function as multi-slide windows resting on a wall portion below and above them.

The configuration of the panels can be designed so they all stack behind each other on one side of the opening or be split to stack on both sides of the opening. Either way, there are two basic options in terms of the way the sliding panels stack. The first is to keep one glass panel fixed or stationary and slide the adjacent panels to stack evenly behind the stationary one. When stacked, some manufactured designs appear as a single panel when viewed from the inside or outside. The other option is to conceal the sliding panels in a wall pocket. In this case the sliding panels disappear altogether, giving the appearance of a full opening in an otherwise solid wall area.

When laying out the multi-slide doors, keep in mind that they are not limited to a single wall plane. Manufacturers have developed methods to allow doors to meet at a corner location such that a post or other element is not needed. That means that when open, the corner virtually disappears, allowing a full visual and physical three-dimensional connection between outdoors and inside. When closed, the door panels come together to form either an inside or outside corner again.

Design Coordination

As noted, multi-slide glass doors can be incorporated into a wide range of building types in a number of ways. They can be fully integrated with the building construction to create a seamless and flush appearance so they seem to disappear altogether when open. In other cases, they can create a large feature in a façade by allowing for a distinctly defined opening. In short, they can be used to work with the overall building design to enhance or even define a particular aesthetic.

When it comes to coordinating the visual appearance of the multi-slide doors with the other doors in the building, it is appropriate to pursue a visual balance with all of the other doors. In that regard, architects often seek doors that can provide clean and even sight lines between different functioning doors to create a consistent daylight opening and complete overall design.

At the basic architectural design level, multi-slide door sizes and proportions can be chosen to match other doors in the building both in proportion or actual size. This can create the desired coordinated appearance at one level. Taking that a step further, it is also possible to select multi-slide doors with stile and rail sizes to match other doors in the building, particularly if all of the doors are sourced from the same manufacturer. This helps to create a complete matching door package with a consistent look that is more refined than having competing visual door components.

Performance Characteristics of Multi-Slide Glass Doors

Having established the clear design opportunities and advantages of multi-slide doors, let's turn our attention to the functional performance. Overall, any window or door product needs to use quality materials that are fabricated to provide a smooth and tight operation. In order to provide a good value to the owner, they must be durable enough to continue to operate well over the life of the building. And they must meet the thermal demands of the climate where they are installed in terms of heat transfer and air infiltration.

Multi-slide glass doors achieve all of these performance needs in a number of ways. Let's start by looking at the materials used to fabricate them. It is most common for the door panels to use aluminum frames surrounding the glass either with or without thermal breaks as may be needed. A unique design innovation based on a traditional wood clad door is an aluminum and wood combination system that is available from at least one manufacturer as well. This aluminum wood frame uses a low-maintenance aluminum exterior combined with a natural wood interior to enhance or blend with the interior design scheme of the building.

With any of these choices, the frame supports and holds the glass itself which can be selected from a typical range of single, double, or triple glazing options. Overall U-factors in the door panels can be achieved at or near the common fenestration target of 0.30 or better depending on specific glazing selections made for low-e or other coatings. The glazed door panels fit into a track running along the door head that the doors are guided along and are commonly made of extruded aluminum with thermal breaks as needed. The track depth will vary to suit the number of door panels used in the multi-slide door. The door sill is also extruded aluminum available in a variety of flush or raised profiles and designed to allow the door to rest and slide along it. The wheels that allow the door panels to slide are commonly made either from nylon for smoother, quieter operation in lighter-weight panels or from stainless steel for heavier-weight door panels. Altogether, the door panel assembly is intended to be more rigid, more durable, and longer lasting than conventional residential sliding glass doors with full customization of the overall door size.

Structural and Weathering Performance

Structural integrity is clearly needed in all window and door units to maintain proper fit and operation of the products under conditions of wind, rain, and other weather stresses. Structural Load Deflection testing is routinely carried out by manufacturers under ASTM E-330. This test is used for multi-slide doors as well with the results directly dependent on the size of the panels.

The American Architectural Manufacturers Association (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 namely 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. Water penetration is tested by ASTM E-547 with the sill configuration routinely having a direct influence on the results. Clearly water entering through a closed multi-slide door wall would be disconcerting at least and damaging to the building at worst. Since such water penetration must not occur, water must either be sealed out completely or managed so that if it does penetrate any part of the system, it will drain away harmlessly. 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.

Thermal Performance

Identifying the true thermal performance of fenestration systems and products has been the focus of a not-for-profit trade association known as The National Fenestration Rating Council (NFRC). Since 1989 they have championed the process of fairly and comprehensively rating windows, doors, and skylights including multi-slide glass doors. Prior to the formation of NFRC, window manufacturers used different tools to measure and report the energy efficiency of their products. In 1993, NFRC developed the first consensus method for evaluating the thermal transmission of windows. NFRC 100 “Procedures for Determining Fenestration Product U-factors” is now the accepted standard for rating windows, doors, and skylights for U-factor. This standard establishes standardized environmental conditions, product sizes, and testing requirements, so that architects and others can make informed choices by comparing the performance of different products fairly and accurately.

One of the most important improvements NFRC 100 offered the industry was that the determination of heat loss of the entire window unit, not just the glazing. A multi-slide glass door that is tested and subsequently rated in accordance with NFRC 100 gets credit for all of the energy-efficient features including low-e glass, thermally improved frames, and even the spacer used between layers of insulated glass. However, if a manufacturer is deficient in any of these areas, the testing will reveal that as well. Therefore, 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.

Beyond direct thermal transfer through materials, codes and standards, along with the NFRC, have increasingly recognized air leakage (AL) as a very significant factor in fenestration performance. Therefore, it is becoming required for fenestration products to meet minimum standards for this leakage or air infiltration and be tested, certified and labeled as such, which the NFRC does. The total system must be able to withstand wind pressures associated with their location and air leakage must be controlled not only for energy performance but for occupant comfort and long-term durability of the fenestration system.

In addition to the AAMA testing discussed, air infiltration testing under ASTM E-283 will indicate cubic feet per minute per linear feet of crack. Multi-slide glass doors address this need to control air leakage, and in the process weather leakage, by using an appropriate mix of perimeter seals on the door panels, usually custom fabricated to match the doors. Top seals can be brush type to allow for the smooth operation of the door but still restrict the transfer of air and weather. The bottom or sill seal may be of low-friction coated rubber applied to the bottom of the door, creating full seal but still allowing for the smooth operation of the door panels.

As the panels come together and interlock, continuous seals along the edges can include compression rubber gaskets, fin brush seals, or both. In all cases, the intent is to provide a tight seal when the doors are closed and maintain the pressure and weather resistant performance as tested.

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 (versus being reflected away) creating heat gains inside a building. This performance factor is usually adjusted through coatings applied to the glass to allow more light (and resulting solar heat) where it may be desired in cold climates, or to allow less where it is not wanted in hot climates. NFRC testing also responds to green building standards by assigning a value to the visible light transmittance (VT) that comes through a tested product. This VT determines the effective light available for daylighting so finding the right balance between how much light and resulting solar heat is transmitted versus how much to exclude needs to be assessed on a project by project basis.

At the end of all of this testing, a comprehensive view of thermal performance of tested products is determined providing a more accurate, credible, and uniform energy rating for fenestration products. The test results are documented through the NFRC Product Certification Program (NFRC 700, PCP) which sets forth the specific requirements for rating, certification, and labeling of a manufactured fenestration product. Manufacturers who participate in the NFRC Certification Program have their products listed in the NFRC Certified Products Directory that contains thousands of certified products and is available on-line at www.nfrc.org. In addition, each tested unit is then shipped with a standard label that identifies the key elements of performance, much the way mileage rating stickers are applied to cars or nutrition labels are applied to food.

The ultimate balancing activity in any design is how much fenestration to use as a percentage of the overall wall area of a building. The energy codes tend to use 40 percent as the benchmark. In some cases, all of this glazing can be concentrated on one or two facades as appropriate to a location. Building designs that use multi-slide glass doors with more than 40 percent window to wall ratios are possible but offsetting measures elsewhere in the building envelope are required. The rationale for this benchmark seems to rely on the fact that a well-insulated wall will inherently perform better thermally than any type of fenestration. Nonetheless they also recognize that only fenestration allows the natural daylight and potentially beneficial solar heat gain into buildings. Simple energy modeling of different scenarios during the earliest stages of design will help to determine the most appropriate balance of opaque wall to fenestration. This is particularly important when different façade orientations (i.e. north, south, east or west) are taken into account since the best performing buildings usually do not treat all facades equally. The talent, experience and skill of the architect used in finding this appropriate balance will determine not only design quality and code compliance, but in a very real way help determine the overall energy performance and utility costs experienced by the owner and users of the building.

Green Building Contributions of Multi-Slide Glass Doors

The green building movement in this country has given rise to quantifiable rating systems that seek to establish specific levels of achievement in the creation and performance of green buildings. The best known of these green building rating systems has been developed by the US Green Building Council and known as the LEED® rating system. The LEED 2009 system is in place until the year 2015 which overlaps with LEED version 4 introduced late in 2013. Since buildings are currently being designed under both systems, it should be noted that credits may be earned somewhat differently for each when seeking certification. With that in mind, the contributions that multi-slide doors can make are generally described within the common green building categories as follows.

Optimize Energy Performance

As part of an overall building envelope design, multi-slide doors can have a big impact on the energy performance due to their contribution to desirable passive solar heat gain when the building is designed to take advantage of it. By incorporating passive solar strategies such as overhangs and building orientation, solar gain can be used to an advantage in the heating season, and reduced in the cooling season. The result is reduced use of purchased fossil fuel energy. In commercial buildings where daylighting is desired, then multi-slide doors can be used to provide an abundance of natural light into the space. With proper controls and lighting arrangements, this can reduce not only the amount of artificial lighting needed but also reduce the associated cooling load imposed from heat given off by electric lighting. The net result is a reduction in electrical energy use. The actual optimized energy performance can best be determined by using energy modeling and adjusting the size and configuration of multi-slide doors accordingly.

Materials and Resources

In some cases multi-slide doors are available with recycled content positively impacting a life cycle assessment of the product. During the construction process, the pre-fabricated, custom nature of the product limits or reduces scrap and construction site waste. During their use in the building, their ability to close and seal tightly will reduce air infiltration and heat transfer. At the end of their service life, the door panels can be salvaged and re-used in other buildings. Manufactured in the USA means regional material contribution is possible and the impact of transportation is lessened.

Indoor Environmental Quality

Large format multi-slide doors provide the notable and desirable addition of daylight and views which contribute directly to indoor environmental quality. In the open position, they also provide ample natural ventilation and exchange of fresh air into the building. Finally, since little or no paints, coatings, adhesives, or harmful sealants are needed in the product, they do not contribute to VOC content in the indoor air.

Innovation in Design

With green design, size matters. Building size is a significant contributing factor to resource efficiency and in the end will affect energy use also. The move to smaller and more efficiently planned spaces makes flexibility, functionality, and expansion capabilities all the more important. Multi-slide glass doors provide a variable connection to the outdoors allowing for living spaces to be smaller while still feeling large.

Specifying Multi-Slide Glass Doors

When specifying multi-slide glass doors, there are choices and specification details to pay attention to so that the best products are selected for the building where they will be installed. The Master Format section number commonly used is 08 32 13 “Sliding Aluminum-Framed Glass Doors.” Some of the relevant items to address in a standard 3-part specification format are highlighted as follows.

Part 1 General

When it comes to specifying the most appropriate multi-slide glass door for a particular building, especially a green building, the first place to look at is testing performance criteria. Make sure to compare similar testing methods between manufacturers and specify accordingly. The appropriate AAMA Product Performance Class should be indicated along with the minimum DP rating. Water penetration should be tested by ASTM E-547 and air infiltration testing under ASTM E-283. Structural Load Deflection testing is carried out under ASTM E-330 and performance criteria should be related to the size of the panels. Finally, and in particular look for NFRC certified and labeled systems to address thermal performance and require those accordingly.

Submittals will be similar to most window and door products for product information and shop drawings if needed. They should indicate full coordination details with the construction drawings and the sizes should be double checked since they are custom fabricated to suit the designed opening. Working with a selected manufacturer during the design process will allow for better coordination in the spirit of integrated project delivery. Other general specification items should include warranty requirements for the glazing, the other materials, and the system overall consistent with available 10 year warranties in the marketplace.

Part 2 Products and Options

Identifying the specific multi-slide door products, materials and options that are desired requires covering several items. If multiple product types are selected for a building, then obviously they each need to be specified and their locations identified on the drawings.

▶ Frame materials: The choice needs to be made between the three commonly available frame materials. Aluminum only frames generally carry the lowest cost, thermally broken aluminum frames address energy efficiency, and aluminum wood frames (with or without a thermal break) address exterior maintenance and interior appearance. Wood only frames may also be available from some manufacturers.

▶ Frame colors / finishes: Since the frames are extruded aluminum, they can be finished in common aluminum color choices such as bronze or clear anodized or white paint. They are also available from some manufacturers in colors to match popular window brands allowing for a consistent exterior or interior appearance with the rest of the building. This would include some of the earth tones, reds, greens, and browns found on popular window brands. If none of these are appropriate, then it is also possible to use a Kynar paint finish to customize the frames to virtually any color. One manufacturer's innovative frame design offers split finish options for the interior and exterior to provide maximum design flexibility. If aluminum wood is selected for the frames, then the wood color or finish should be specified from such options as vertical grain Douglas fir, mahogany, maple, oak, walnut, or even dark cherry.

▶ Glazing: With the frame selected, the glazing infill options need to be finalized. Typically, most applications use double pane insulating glass units with low-E coatings and inert gas fill for energy efficiency. Single and triple glazing are also options as the location may warrant. Specialty glazing may also be available with obscure, acoustic control, impact resistant, art glass, or even solid material possible to be specified.

▶ Tracks and Sills: The configuration and make-up of the upper tracks are usually determined by the configuration of the multi-slide doors. The profile is matched to the door manufacturers system for hanging the door while the number of tracks will match the number of stacking panels in the multi-slide assembly. They are typically installed flush with the ceiling or head of the door opening but their height should be known and verified to determine the proper rough opening height. Similarly the sill needs to be coordinated and will match the manufacturers system and number of door panels. Sills are available in at least three different profiles and should be specified according to the project design needs. Flush sills are intended to be recessed into the floor such that they are level with the finished floor surface and can incorporate the same finish flooring between the sill tracks. Raised sills are intended to set up above the outside walking surface and may come in varying interior leg heights to create a greater degree of weather resistance. These raised sills can be made ADA compliant when needed by virtue of a ramped edge when there is more than ½ inch change in the sill height compared to the walking surface. Regardless of type, sills are typically thermally broken and should specified accordingly. The wheels that fit into the track and sill can also be specified between nylon plastic and stainless steel although large or heavy door panels will generally require stainless steel.

▶ Hardware and Locking: Hardware is often provided by the manufacturer of the multi-slide doors since it necessarily needs to be recessed so as not to interfere with the door operation. Recessed hand pulls are common on door panels and sliding locking mechanisms are generally used on the primary or end panel. The lock itself relies on recessed or concealed locking at either two or three points depending on the height of the panels. Some manufacturers offer a sliding locking mechanism with an exterior keyed lockset providing easier access when the door is locked while still maintaining greater security. Although there may not be many choices in hardware or locking mechanisms, there is a choice of hardware color that can be specified to match the rest of the project.

▶ Automatic controls: It is possible to specify doors that are moved manually or with an electric operation. In that case, the space required for the electric motion devices, wiring, and control pad must all be designed in and specified. Since this is something that will vary between products, it is best to work directly with a selected manufacturer to determine what is available and how to coordinate its installation. Similar to other automation devices, both wall mounted and handheld remote options may be available to open, close, lock, and unlock a multi-slide glass door. Some can even be linked to a smart phone or as part of a whole house automation system.

▶ Screens: In areas where insects are an issue, then adding screens to the opening is an option. There are two types available for large openings. A non pleated screen mesh and blind that is fabricated as an integral part of the door or a more economical alternative to specify is the pleated mesh screens that collapse and move out of the opening allowing for maximum open space. From an aesthetic standpoint, both the non-pleated and pleated screens remain concealed and out of view when not in use.

Part 3 Installation

Installing multi-slide glass doors requires appropriate attention to detail to assure the desired outcome is achieved.

▶ Installation requirements: Sliding doors will require some attention on all sides of the opening, but the critical element here will be the installation of the track and the sill. Placement needs to align with the elements of the building that are intended to support the door and integrate with the finishes. The track length and location will depend on whether the door is a bi-parting design or a single sliding design and adequate clearances will be needed in either case. Once the track and sill are secured, then the doors can be set into place. If the sliding door is electrically operated, then the operator will need to be installed, the control pad located, and the electrical connections made.

▶ Cleaning and maintenance: Regardless of the door details, the final installation steps include final cleaning and testing. The door should operate smoothly and close securely in all cases. The seals should engage and prevent air leakage between inside and outside. From a maintenance standpoint, the doors should be routinely checked to be sure they continue to perform over time as when they were installed. If not, they should be repaired promptly by qualified personnel to prevent energy loss or weather penetration.

Conclusion

Multi-slide glass doors offer architects the ability to create flexible spaces that are able to seamlessly connect the outdoors with interior spaces, provide daylighting and natural ventilation, and capitalize on available views. Selecting glass door panels with thermally broken frames, low U-factor glazing, and complete edge seal systems can help the building capitalize on available passive solar energy while controlling unwanted heat loss. Because of their flexibility, range of options, and custom fabrication, multi-slide glass doors can be used in different building types as varied as single family detached residential units to commercial spaces to hospitality and education facilities. Working with manufacturers early on in the design process can help create buildings that are vibrant, sustainable, and durable over the long term. Overall, they are worthy of consideration on any project where clean lines and large open expanses of glazing are a part of the overall design of an elegant and quality building.

Peter J. Arsenault, FAIA, NCARB, LEED AP, practices architecture, consults on green and sustainable design, writes on technical topics, and presents nationwide on all of the above. www.linkedin.com/in/pjaarch

LaCantina Doors is the leader in designing and manufacturing products that create large open spaces. Offering the most innovative and comprehensive range of folding, sliding and swing systems available, LaCantina Doors utilizes the same signature narrow stile and rail profile across its product line for a complete and perfectly matching door package. Designed and made in California, LaCantina Doors have contributed to award winning projects ranging from residential, retail, commercial, educational facilities, resorts and is the preferred choice when it comes to products that open spaces. Backed by an industry leading warranty, LaCantina Doors are available across the U.S. and Internationally. www.lacantinadoors.com