• Look for ghouls, goblins and super heroes on your doorstep tonight, but don’t expect many miniature suit-wearing insurance underwriter wannabes.

    I’ve seen several comments recently regarding whether safety glass installed in storefronts prior to 1977 should be replaced, or if it is grandfathered. I’m surprised this situation isn’t caught and resolved through insurance underwriting.

    Don’t the insurance companies weigh in on liability insurance and inspect a business’s premises the same way they do homes? When my wife and I bought our current home, we had to schedule the insurance people to walk through it before closing so they could confirm the roofing type, distance to a fire hydrant and other details. They even pointed out one or two things that needed to be done in order for them to carry the policy.

    Isn’t this same thing done with business insurance coverage? For example, it seems like a lot of the reduction in job-related injuries over the years has been insurance-driven. The insurance carriers come in, inspect the premises, make recommendations for changes and underwrite what’s being done correctly. It’s a pretty pro-active process, making changes before someone gets hurt, not afterwards. I wonder if the storefront glass in a restaurant, in the old hardware store downtown, at Bill’s Barber Shop on the square, etc., is one of the things insurers inspect when they walk the premises.

    I’m not advocating that insurers be the safety police; it’s just curious how potential code compliance problems end up getting past them.

    On a different note, I was glad to see that the recent ill-informed suggestion to use wired glass as a bullet-resistant material was spit back out as quickly as it was put out there as the hokum it is. I was proud to see the reaction from some of our industry people who know the ins and outs of glass. Traditional wired glass is not impact or bullet-resistant, so it is not really a defense against school intruders.

    Compared to annealed glass, traditional wired glass was considered 50 percent weaker than annealed glass in some of the older codes. The wiring isn’t all that strong. I get the fact that the wires might remain captured around the edges, and that might be a deterrent. But with a gun, how does it block any subsequent shots after the first one that shatters it? The wire’s not strong enough or sufficient to stop bullets on its own. And the self-described “expert’s” statement didn’t come with any backup or testing, just that the wire had stayed in the opening.

    Lastly, in honor of Lyle Hill and his quotes of the week, I offer this one I heard recently from Loren Supp, AIA, lead designer with Gensler in Seattle: “Architects try to take science and synthesize it into art.”

    Tags: ,

  • Or so I thought. Someone asked me recently if I knew how large a piece of glass needed to be to resist a certain wind load. I don’t know why I remembered I had it, but a chart from the 1970 UBC used to be what was used to figure out if glass was strong enough for wind loads.To use the chart, you found where the the thickness of the glass shown along the top row intersected with the wind load column on the left. That number was the maximum square footage of glass allowed for that wind load. Example: ¼-inch glass, 40psf wind load = 27 sq.ft. maximum glass lite size, regardless of the height and width. These values represented a “fresh off the float line” strength of annealed glass.

    Referring to another table, you could then increase the 27-square-feet allowable lite size by incorporating it into an insulated unit (27 x 1.5 = 40.5 sq.ft.), heat strengthening it (27 x 2 = 54 sq.ft) or tempering it (27 x 4 = 108 sq.ft). The factors could be combined, such that a heat strengthened, insulated unit could be, at 40 psf, 27 x 1.5 x 2 = 81 sq.ft. That’s assuming, too, if you heat treat one lite, both lites in the IGU had to be heat treated one way or another.

    These charts were developed primarily by glass manufacturers. Easy, right? Not so fast, kemosabe!

    The good folks at ASTM came along and developed ASTM E1300 “Standard Practice for Determining Load Resistance of Glass in Buildings,” which addressed more factors. According to Bill Lingnell, the old UBC charts didn’t take into account weatherability, and they used a statistical probability method following a normal distribution curve. By contrast, ASTM E1300 was developed using a failure prediction method, and also accounted for glass weathering. The IBC since has generally adopted ASTM E1300 as the glass strength standard.

    Currently, there are a lot of companies offering ASTM E1300 software that will confirm the glass construction – insulated or monolithic, heat treated or not, laminated, etc. – and whether it will work for a given wind load.

    Some programs will also calculate how much the glass deflects. If you’ve ever been in a completed building, and the occupants call in with a complaint that “the glass is about to fall out,” you know about this part of the discussion. Occupants aren’t used to glass that moves like a trampoline under certain exterior wind conditions. Glass deflects equally when annealed, heat strengthened or tempered. It takes approximately four times the force to break a tempered lite compared to one that was annealed, but both still deflect the same under the same load.

    Some architects ask about limiting the glass deflection to 1 inch. This is a human comfort thing, as there’s nothing in the codes and/or in the glazing industry that limits deflection. In most instances, the means to limit deflection on larger lites or in areas with greater wind load is to increase the glass thickness. Most framing systems don’t easily accommodate varying glass thicknesses (i.e. 1” IGU in typical vision areas, 1¼” thick in higher wind load zones). Vision and spandrel glass thickness differences used to be a common practice, but have virtually disappeared due primarily to energy constraints. The software, too, will allow one lite to be different than the other, be it tempered, heat strengthened, or laminated while the other lite stays annealed. The UBC charts didn’t do that.

    But that’s all the software will tell you. It won’t reveal whether the glass needs to be tempered, or if safety glazing is needed because it’s in a door, is adjacent to a door, or because it is adjacent to a walking surface where no handrail or horizontal is present. It also won’t tell you that safety glazing is required if the sill is lower than a certain height off the floor, or if there’s a horizontal or handrail 3’-0” to 3’-4” off the floor so that if the glass breaks, someone won’t fall through the opening.

    Software also won’t tell you if the glass should be heat treated at inside corners for sun-facing surfaces. Glass doesn’t always allow all of the sun’s energy to pass through it, some is reflected, and if that reflection is onto another glass surface, the lite on that adjacent surface may need to handle more than just direct thermal energy. Reflective metal panels may have reflective effects on adjacent glass, also.

    Other factors that affect glass substrate selection or make-up are reflective coatings and tintings, to name a few.

    The lesson here is you can trust software, just know what it’s doing, and more importantly what it’s not telling you. Although many of the old rules don’t work as well as they used to, one that still holds true is: when in doubt, call the glass manufacturer. Their tech staffs are able to help with these types of issues. It’s nice to have a second set of eyes to help get your project right, both in the estimating and execution phases.

    Lastly, PLEASE NOTE: Any comments on this blog that deal with my age, especially from Greg Carney, will be deleted with prejudice!

    Tags: , ,

  • I’m not good at music trivia, and I won’t claim to have a favorite song. My car radio  has buttons set to country and classical stations, news, oldies, easy listening, and one or two stations the kids liked –  heaven knows why. Yet, when it comes to the Beatles, I can’t remember a time I haven’t been able to sing all the words to their songs. Now, here’s a building that takes to heart their song “I’ll Follow the Sun.”

    This is an instance of something on paper looking good, but in practicality, can they make the building change orientation?  And conceptually, as the article points out, having solar panels on some sort of “moveable mounts” makes perfect sense, as the sun’s never in the same position throughout the day and seasons.

    Based on the geometry, fixed solar panels typically are set to an angle perpendicular to the sun at solar noon of the spring or fall equinox. At that fixed position, they are 100-percent efficient. But,  as the sun moves east to west and up and down in attitude during the course of its journey across the heavens, its rays will be perpendicular to a fixed panel for brief moments, possibly only twice a year, depending on how they’re set. And when the rays aren’t perpendicular, the panel’s efficiency drops off.

    Curved or parabolic reflectors attempt to overcome that inefficiency by capturing and/or focusing more rays to a collector. Most of these collectors change their angle in relation to the horizon or to the travel east to west, thus offsetting that part of the sun’s journey.

    But an entire building that twists to follow the sun? The structure would have to be substantial given the load transfers, both for the building’s weight and wind loads at the staggered floors. Maybe those end walls shown in gray in some of the conceptual drawings are just pure structure, with no way of permitting even the smallest of windows.

    I guess it could work to twist the whole of the tower east to west and returning it to the east to face the sunrise in the morning. But, buildings are heavy. To get the whole of this new “Twilt” building to twist, can you imagine the machinery to move it, let alone the size of the turntable the building would be constructed on (basically the foundation so that it wouldn’t tip over, also), and the force required to start that rotation?

    Additionally, the solar panels themselves would be cantilevered off balconies or extended slab edges, which could then be mechanically moved to orient them to the sun’s attitude, much like the parabolic collectors mentioned above. In combination with the turntable, this could make the venture credible.

    But realistic?  Is there a developer out there prepared to spend this kind of mullah, and are there users, be they office or condominium buyers, willing to pay the rent or purchase price?  That’s obviously a decision way above my pay grade, and it’ll be interesting to see if this turns into reality.

    An idea just occurred to me. Maybe the “death ray” buildings we’ve recently read about are missing the mark, and with a little work could be made to serve as productive solar collectors and not death sources from the sky. Maybe the architects could design curved surfaces into buildings and focus the sun’s energy on a focal point on the ground that can collect the rays and turn them into electricity. It might require land and the collector might have to move as the focal point of the sun’s rays change.

    I’d love to see how that concept would play out in the shape of a building. Wouldn’t you?

    Until then, as the Beatles sang, “And now the time has come, and so … I must go.”




USGlass Magazine

USGlass Magazine