WINDOW TECHNOLOGIES: Assembly
Manufactured Window Units
The material used to manufacture the frame governs the physical characteristics of the window, such as frame thickness, structural concerns, weight, and durability, but it also has an impact on the thermal characteristics of the window. Manufacturers are beginning to produce hybrid or composite sash and frame units, in which multiple materials are selected and combined to best meet the overall required performance parameters.
While it is useful to understand the role that frame type plays in window thermal performance, the frame U-factor is not normally reported by manufacturers. The window U-factor, as given on an NFRC certified rating or label, incorporates the thermal properties of both the frame and the glazing. The remainder of this section describes aluminum, wood, and vinyl frames, and introduces some new frame materials that are commercially available.
Curtain walls and Storefronts
Similar to a glass curtain wall, a storefront is a system of doors and windows mulled together as a composite structure. Storefronts are typically designed for high use and strength. A storefront system is usually installed between floor and ceiling on the street level of a building.
Aluminum is used almost exclusively as the frame material in both curtain walls and storefronts. Some steel is used as well, but is often clad on the exterior with aluminum or stainless steel caps. For larger glazing areas, the structural strength and durability of aluminum and steel cannot be equalled by other materials.