This course is part of the Glass and Glazing Design Academy

Installation Guidelines for Storefront Glazing System

For most projects, a storefront glazing system is designed for optimal performance with applications having 4- to 5-foot spacing between vertical mullions with spans generally up to 10 to 12 feet. Manufacturers can provide guidance on exact limitations of glazing products, so it is important to engage the glazing manufacturer early in the design process.

System depth is usually between 4 inches and 6 inches, with system widths, often referred to as “sightlines,” varying between 1 ¾ inches and 2 inches. Due to the nature of the application, storefront glazing systems are not required to span large distances, so overall system depth can be smaller than that of a curtain wall system.

Thermal performance of a storefront glazing system is impacted by the type and style of glazing, installation methods, and thermal bridging. Depending on the climate zone and thermal performance requirements, a storefront system can be either non-thermal or thermally broken. The most typical thermal break method is a small pocket located somewhere in the middle of the extrusion filled with a polyurethane material and mechanically de-bridged to isolate the interior and exterior sections of the extrusion. This is commonly referred to as a “poured and de-bridged” thermal break.

Image courtesy of NGA

Here is an example of a storefront horizontal mullion with dual pour and de-bridge pockets (highlighted in green).

Image courtesy of NGA

Here is an example of a storefront horizontal mullion with mechanically crimped thermal isolating struts (highlighted in green).

Typically, a storefront glazing system is internally drained. This means that any water infiltration is captured in the horizontal member and diverted to the vertical and/or the sub-sill, where it weeps out of the system to the exterior. These systems are dependent on the quality of the internal seals to provide the lower water resistance they are designed to meet.

A storefront glazing is typically designed with three different assembly methods commonly known as screw spline, shear block, and stacking. Screw spline and shear blocking approaches enable glazing contractors to preassemble single units either in a shop environment or directly at the jobsite, while stacking happens on the jobsite. In all three methods, the vertical members typically run continuously while the head, horizontal, and sill members are attached between the verticals.

Image: Kawneer; courtesy of NGA

Screw Spline Method.

Screw Spline Method: The screw spline method involves using mating mullions during the fabrication process. Vertical mullions are designed in two sections so that horizontal members with integral screw races can be fastened with screws to each vertical half, forming a bay. Each bay is then snapped together during installation at the jobsite, with the screw heads not exposed in the final installation. This method is popular due to its ease of fabrication, assembly, and installation. To ensure proper water management, install water diverters at the intersections of the vertical jambs and horizontal members, and add end dams to the sill flashing to prevent water infiltration.

Image Kawneer; courtesy of NGA

Shear Block Method.

Shear Block Method: The shear block method, also known as the can system, is similar to stick curtain wall systems. In this method, horizontal members are attached to tubular vertical mullions that have screw-applied shear blocks. The horizontal members snap- or slip-fit over the shear blocks and fasten to them. Ensure that the horizontal locations are caulked at the shear block locations for a watertight seal, preventing water from penetrating the substrates and leaking into the building.

Image Kawneer; courtesy of NGA

Stacking Method.

Stacking: The easiest method of installation is a stacking storefront system which refers to the way it is assembled in an opening. Typically consisting of a continuous head and sill “gutter,” the vertical mullions are installed into the gutters and inserts cut to the daylight opening are then snapped into the gutters, holding the previous vertical in place. Each successive bay is stacked into position. Intermediate horizontals are usually attached to the vertical with shear blocks. Getting the details of installation correct is critical for the success of the project. "When designing exterior fenestration systems like storefront, window wall, and curtain wall, it’s critically important to specify exactly what you want and what you need. We always start with the required structural performance for the condition, says Billy Strait, vice president of business development for Oldcastle Building Envelope, a leading supplier of value-added, glazing-focused, interior and exterior products and services. “After that, we make recommendations based on the functional application and aesthetics. Without precise specification documentation, the contractor may bid something that misses the design and/or performance intent. There are many options with these products, so specifics are important."

Storefront window systems tend to be lower in cost per square foot than most other glazed framing systems because the overall requirements to withstand high pressure, water infiltration and thermal performance are generally less than other window systems. In general, storefront window systems are simpler and easier to install than more sophisticated window wall or curtain wall systems. Likewise, because structural requirements are less, the installer need not be as experienced, which provides some relief on installation costs. However, though installation may seem more straightforward, it is critical that storefront window systems be installed correctly to ensure the window performs as required, and special attention must be given to properly seal the internal joinery to control air and water infiltration within the system.

"When it comes to architectural design, the choice between storefront, window wall, and curtain wall systems hinges on the specific needs of the project,” says Joe Erb, National Accounts Manager for Quanex, a global, publicly traded manufacturer of building products that include insulating glass spacers, vinyl profiles, window and door screens, cabinet components, fenestration components, and vinyl extrusions. “Each system offers unique advantages, from the aesthetic appeal of a storefront to the robust protection of a curtain wall, and the balance of both with window wall. Know and understand the strengths and limitations of each system when specifying the envelope. The right choice will enhance both the functionality and beauty of the building."

Window Wall Systems

Window wall systems are an assembly of pre-glazed windows installed between floor slabs, making them suitable for mid-rise to high-rise residential and commercial buildings. This system spans between the floor slabs and is recessed from the slab edges or between spandrel construction of other glazing systems, such as precast concrete panels, metal panels, or masonry.

The windows are sometimes described as “ribbon” windows, as the long horizontal bands that are created can appear to be a ribbon around the perimeter of the façade. These systems provide a high degree of flexibility in design and can be adapted to various building configurations, from office spaces to hotels. Additionally, window walls allow for ample natural light, improving the indoor environment and reducing the need for artificial lighting.

Photo: YKK; courtesy of NGA

This image shows the structure of a basic window wall glazing system.