Volume 42, Issue 4 - April 2007

the Farnady Files
Walking on Glass: Looking Closely at Glass Flooring Applications
by Dez Farnady

Back in the days when I spent my summers on the beaches of Southern California, ďwalking on glassĒ usually meant stepping on a broken beer bottle left behind from a beach party that took place late the night before. There was a lot of that going on back in those days. Donít let your kids know that, though, because they think they invented parties. Fortunately, for most beach goers, glass comes from silica sand and it does not take long on the beach for it to return to such a state. The sharp edges of broken glass are ground down quickly as if they had been sandblasted just to save our bare feet. 

In a more civilized world, walking on glass could be dated to when glass block was first used as flooring to let light into basements. Glass block is just about 100 years old now, and is still a masonry item as far as the glass industry is concerned. Application and installation of glass block is closer to its cousin the brick than to its brother the float glass.

So, while walking on glass block may be old hat, walking on float glass is another matter. Since the floor is not a part of the glazierís world when glass-walking surfaces are designed into a project, some contract glaziers are faced with an unfamiliar situation. The designerís natural instinct is to take his glass floor concept to the glass guy and the glazierís response is to think of it the same way he thinks of vertical glazing. This obviously is not a good idea. 

Step Carefully
The phone calls I typically get are with regard to the thickness of the glass. My usual response is to send the customer to the right placeóto the people who make glass floors and stairs. Floor load requirements may not be difficult to meet, but that is the least of the problems. The people who design and engineer glass floors know they have to consider structural support, the strength capacity, the slippery nature of the surface, transparency questions and a whole lot of other floor-related items that have little to do with the vertical glazing business. 

One type of flooring, made with multi-layered glass laminates, is able to generate more than adequate strength to meet some serious load requirements, so they come in handy in the world of the snow-loaded and the ďground levelĒ skylights. Snow loads on skylights in the High Sierra, for example, can range from about 160 pounds per square foot at Lake Tahoeís lake level to as much as 300 pounds at elevations more than 10,000 feet. Three hundred pounds per square foot exceeds most floor load requirements by a long way.

New Applications
The newest in-between place thatís neither window, nor floor nor skylight is the ground level light-well light source. I am not sure I want to call this a skylight because, like a glass floor, this also has its own special requirements. First of all, it must function like a window because itís used to provide outdoor light to the underground portion of the house. This design has become common in areas where the size of a house cannot exceed the specified footprint and there are also building height limitations. In these cases the housesí added space goes underground. To maximize the available light, these windows, that are not vertical, are usually nearly flat or on a minimal slope. They have all of the water exposure and drainage issues of skylights and are almost, but not quite, floors. 

The requirements for these applications are much like those of masonry, in that they lean up against stucco or masonry walls and are usually surrounded by all sorts of trim and brick or decorative stonework. And since they are generally ground level, you have to be prepared for the possibility that someone could step on them or fall on them. Interestingly enough, there are no code requirements that I know of that treat this application any different than if it were vertical glazing adjacent to a walking surface. (Editorís note: Section 2405 of the 2006 International Building Code does address sloped glazing applications.)

I am sure the first major injury will bring out all the lawyers, but until then I am not going to be the guinea pig. I donít want them practicing law on me. In fact, per my companyís policy, any ground level application, be it ground-level, light-well cover or skylight adjacent to any kind of a deck or walking surface, comes with a warning that local codes probably require handrails to surround the glazed area. Of course, the glass automatically gets changed from standard skylight lami to 5⁄16 or 7⁄16 tempered or heat-strengthened lami with a .060 interlayer that even meets UL 972 for forced entry. You are not likely to see someone get through that. Thatís a simple precaution that protects the homeowner or his guests from possible injury. And, obviously, protects us from possible liability claims. Thatís what we do and I suggest that you do at least the same. 

the author: Dez Farnady serves as the general manger of Royalite Manufacturing Inc., a skylight manufacturer in San Carlos, Calif. His column appears monthly. Mr. Farnadyís opinions are solely his own and not necessarily those of this magazine.


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