Volume 36, Issue 1, January 2001

The Big Question

What the Heck is Spandrel Anyway?

by Dez Farnady

     Don’t look it up in a dictionary, or worse yet an encyclopedia, because you will be more confused than ever. The books will explain it by identifying spandrel (which also can be spelled “spandril”) as the triangular area outside the curve of an arch, and that is not the definition we are after. Spandrel glass, as we know it in the glass business, is the glass typically used on the exterior of the building to cover up the area between floors. Curtainwall and storefront systems provide the framework for an external glazing skin allowing the entire building exterior to be covered with glass. The spandrel glass portion covering the structure between the floors with non-transparent colored glass lites is often designed to match the glass in the vision area. This is particularly true with reflective products that are used as an effective way to cover up the structure and retain a uniform glass skin where you can’t tell the window from the wall.

The typical high-performance reflective product has a light transmission low enough that the appearance of the glass with normal interior lighting behind it can be matched in the spandrel area with the simple application of a vinyl opacifier. So, in a sputter-coated (high-performance) spandrel the only difference between the vision lite and the spandrel glass is the fact that the spandrel is opacified.

     The standard application for non-reflective glass and tinted products is done with a fired-on frit process. A colored ceramic glaze or enamel is painted, usually on clear glass, and is fired in a tempering furnace where the glaze melts, vitrifies and fuses to the glass surface forming a permanent bond. This is the most common and most durable spandrel glass with only a few drawbacks. The nature and cost of the ceramic glazes makes the color range somewhat limited. The application of the glaze and firing tends to leave pinholes and shows uneven paint applications when backlit.

     The advent of the Solarcool and Eclipse products has created more opportunities for designers, because glass can be installed with the reflective side either in or out. When frit is applied to the non-reflective side of this type of glass, it takes on the appearance of a front surface mirror. To enhance the color look, you turn the reflective side in. Unfortunately some of these online-coated reflective products don’t do well with frit because frit fired on to the reflective coating tends to burn or damage some of the coatings. So the newest spandrel product on the market has to be used to accommodate the second surface reflectives. This new product is a silicone-based paint that has a far greater color range than frit and does not damage the surface when applied to the reflective coating. The warranties run ten years and the jury is still out on the durability, but the product looks pretty good.

     None of these products is an easy one with which to work. With the high-performance products it is very difficult to identify the particular type of high-performance glass. Even though the opacifier is all the same, there are far too many coating colors. With frit products there are so many similar dark colors of bronze and gray that you can’t tell one from the other. Some old buildings glazed with bronze spandrel (where there is a high incidence of breakage) take on a checkerboard look in the late afternoon sun, resulting from the mismatched lites of the replacement spandrel. No one retains the original records to be able to determine if the color was solar-bronze or harmony-bronze or harmony-solar-bronze or lava-bronze or maybe if it was harmony-solar-gray.

      The other spandrel problem is that none of these products can be used as vision area glazing lites. This, of course, is only a problem when designers don’t understand the application and the contractor installs it. Then everyone screams at the glazing contractor, “Defective—replace it.” Sorry pal, what you see is what you get.

      I will share one secret with you. There is a way to use spandrel as a glazing lite in a vision area. (No one but you knows this.) If you put two pieces of spandrel in the glazing pocket back to back separated with a piece of half-inch sheet rock, you will have supplied an effective glazing panel. It is attractive from both sides and it is done using spandrel glass. It may end up being a bit pricey but I don’t know of any other way to do it.