Factory-Sealed Double Glazing
This is a factory-fabricated, insulating-glass unit composed of two panes of glass separated by a dehydrated airspace. This type of sash is also manufactured with three panes of glass and two airspaces, providing additional insulation against heat flow or sound transmission. (See Fig. 11.35e.)
Heat loss and heat gain can be substantially reduced by this insulated glass, permitting larger window areas and added indoor comfort. Heat-absorbing glass often is used for the outside pane and a clear plate or float glass for the inside.
However, there are many combinations of glass available, including several patterned styles. Thickness of glass and airspace between can be varied within prescribed limitations. In the selection of a window for double or triple glazing, ac commodation of the overall glass thickness in the sash is an important consideration.
Gaskets for Glazing
Structural gaskets, made of preformed and cured elastomeric materials, may be used instead of sash for some applications to hold glass in place. Gaskets are extruded in a single strip, molded into the shape of the window perimeter, and installed against the glass and window frame. A continuous locking strip of harder elastomer is then forced into one side of the gasket as a final sealing component. Fit and compression of the gasket determine weathertightness. With proper installation, calking is not ordinarily required; but should it be necessary, sealants are available that are compatible with the material of which the gasket is made.
There are many variations in the design of lockstrip gaskets, some of which are shown in Fig. 11.36. The two most commonly used types are the H and reglet types. The H gasket fits over a flange on the surrounding frame (Fig. 11.36c and d), whereas the reglet gasket fits into a recess in the frame (Fig. 11.36a and b).
When gaskets are used in concrete wall panels, the entire opening should be cast within one panel. In all cases, the smoothness, tolerance, and alignment of the contact surfaces are very important. The gaskets shown in Fig. 11.36e and Æ’ for use with double glazing require weepholes to allow water that may collect in the gaskets to drain.
The maximum glass area recommended for glazing with standard H-type lockstrip gaskets may be obtained from Fig. 11.37. Loads for the chart are based on minimum glass thicknesses allowed in Federal Specification DD-G-451c. Glass producers should be consulted to obtain the latest thickness recommendations.
