Top 5 Structural Glass Misconceptions
There are a lot of misconceptions about point-supported structural glass systems out there. Having over 30 years experience in the structural glass business, we’ve heard a lot of reasons why structural glass systems are “value engineered” out of a project early on in the design phase from architects and contractors alike. If you’re a designer or a building owner interested in using structural glass systems, you’ve probably heard a few of these concerns yourself during project discussions. In this blog, we’ll have a look at the top five misconceptions about structural glass systems (counting down to the biggest misconception) to help put your mind at ease. This perspective is taken from the system manufacturer/installer’s point of view… someone that provides budgets for these every day. Experience says, “Ask more questions to become more knowledgeable. Don’t always believe the hype.”
5. Structural Glass Systems are Too Expensive!
How often have we heard this one? Cost is one of the first things that comes to mind when a consultant, general contractor, or construction manager looks at a potential component for the building. It can be tempting to throw out a square foot number on something that scares off the architect/client from using a particular type of system. However, it is important to understand that there are many factors that determine the price of a structural glass system. The module width and height, number of points of support, glass make-up (thickness and performance) required, back-up structure, etc. are all important factors to understand. These factors should be considered based on project requirements like wind load, live load deflections, seismic criteria, maximum snow drift load (if a canopy or skylight), acoustics, and any impact or blast resistance criteria before any budget pricing takes place. Many of these items can be quickly vetted out by a structural glass systems engineer before an arbitrary number is put on the table. Be sure to speak with a point-supported structural system manufacturer on approximate rough budget costs before going too far down the road with details. They can best advise you of potential cost savings measures by modifications in design if there is a budget range in mind. System pricing can vary greatly depending on requirements. We can help advise of the best solution within a prescribed budget.
Additionally, glass types and make-ups are rated at different optical and thermal performance levels. Finding the one that is right for your project depends on the unique requirements of the building. For example, the type of glass you choose can strike a balance with visible light transmittance, thermal performance, and the type/size of HVAC mechanical heating and cooling systems used. This trade-off may provide a cost savings in building overhead and maintenance by downsizing the HVAC system by using a slightly more expensive high-performance coated structural glass make-up. It also depends on the amount of glass. A project that uses a larger amount of structural glass area will have a better economy of scale on a cost per square foot basis. It’s all a balancing act.
This is why it’s important to have a system supplier on board early in the design process. At the very least, making a call or exchanging an email with some sketches with a supplier to discuss up front budgets can put to rest many fears about the cost of these systems.
4. I’ll Just Spec the Same Glass I Have in the Aluminum-Framed Curtain Wall for the Point-Supported Structural Glass in the 088000 Specification Section to Match.
It can be tempting to use the same glass that you’ve already specified elsewhere, but it is important to understand that structural glazing components are inherently more expensive than standard curtain walls. The rigors put on point-supported glass to limit deflection and stress at specific points without risking breakage at the holes or fittings are much higher than the edge loads of that on a continuously supported unit backed up with aluminum mullions. Structural glass requires much heavier make-ups than typical one-inch insulating glass units. Often the outer lite needs to be stiffened using ⅜” or ½” glass and there are special “bosses” that transfer the load through the holes. The whole unit needs to be flexible to a certain degree while maintaining the air seal. In the event of over deflection, the PIB sealant shears allowing condensation to form inside; this is also known as a seal failure. It’s very important to make sure the glass and fittings are manufactured and engineered together to help prevent these types of issues.
Above: Photo of Pilkington Planar™ “boss” in an insulating glass unit.
Each project requires different kinds of glass. Coating and size availability, required thicknesses, product sourcing, roller-wave flatness (optical distortion), fabrication tolerances, interactions with fittings, and system warranties are all important aspects of structural glass that you have to take into consideration. We recommend using a separate spec section. Section 089700 can be used for the structural glass wall system specification, which should include glass type and make-ups as it is integral to a complete system warranty. The Pilkington Planar System™ carries a 12-year complete system warranty covering design, engineering, materials and labor. It’s one of the most comprehensive in the industry. Other manufacturers may offer only component warranties on glass, fittings and engineering separately or offer other coverage durations. Be sure to ask to get a sample warranty to better understand exactly what is covered by the vendor.
Again, you won’t know the kind of glass your project requires until you speak with a structural glass system supplier. This will prevent major problems later in the bid phase due to increased glass thicknesses and system costs. Each vendor will do their own calculations in most cases, but it is important to get an idea going in from a budget and design standpoint.
3. I Don’t Want to Draw in Anyone’s System Details. The Details Will Show the Intent Only.
Point-supported systems like Pilkington Planar™ are designed specifically on a case by case basis to be tailored to individual project requirements. Therefore, not all projects use the same fittings. They are customized as required, but work off of a similar design concept. Without discussing the project with a structural glass vendor, it is entirely possible that your design may not be possible as envisioned.
The design principles for the Pilkington Planar™ are proven through in-house and independent laboratory testing. Be sure you review test reports from structural glass system manufacturers to verify these systems meet or exceed the design criteria for your project. If these reports are not satisfactory or readily available, be sure to require that specific tests be performed in the specifications. This will ensure you are receiving the highest quality product to limit potential liabilities down the road.
2. I Want a Competitive Bid. I Need to Include Multiple Glass Suppliers in the Spec.
A common line of thinking is that you choose a company to do all the design work and budgeting, and then pick three or four other structural glass suppliers as alternates that meet specifications. The problem with this thinking is that the vendors may not always be qualified to meet all of the same system requirements specified. More often than not, they don’t meet all of the requirements, so be sure to do some research to check them out. There are many companies that only make components (glass, fittings, structure) and then subcontract out engineering services or vice versa. If this is the case, how can you know who is really responsible for manufacturing the “system” if there is an issue? Is it the glass manufacturer, the fitting supplier, the engineer or the installer?
Do your homework to make sure the quality level of the bill of goods expected to be installed on the project is what they actually get. Make sure the list of approved manufacturers specified meet all of the criteria of the basis of design. This isn’t as easy as picking names out of a directory or performing a Google search for “structural glass”.
When glaziers bid a specified structural glass system, they are usually looking to have a fully fabricated and engineered package to install. There is a high degree of risk in attempting to bid an unspecified product, let alone the additional time it takes to cobble together a system and get it tested to pass to meet spec in most cases. If a substitute was proposed and rejected or the quality level installed was not acceptable, they may not get paid until approved or replaced with an acceptable product. They bear the ultimate risk being accountable for providing systems per the bid contract construction documents. Their livelihood is based on providing a properly warranted product installation that meets owner expectations to help them to secure the next project.
Unfortunately, in this day and age, we have seen glaziers come and go. Even long-term businesses have closed their doors due to tough economic conditions. A structural glass system warranty from a glazier, usually covering only a few years, will certainly not suffice in most cases. You want to make sure the system is warrantied by a reputable manufacturer that can stand behind it for many years to come.
1. Glass is Glass and Structurally Glazed Systems Look Pretty Similar.
This is one of the biggest misconceptions in the glass industry that is shared by many people inside and outside of the architectural community. In essence, yes, all glass products act as a translucent enclosure or cladding to keep the weather out. However, there are many differences in quality, performance, and perceived value. A great reference point in understanding these differences in fabricated glass products is by comparing two brands of cars like Kia versus Cadillac. A Kia comes with many standard features. It can get you from point A to point B and comes with a warranty, but would you say it’s interchangeable for a Cadillac? Do they look and perform identical? Most people would say that they are not the same level of quality and performance. Even if some of the visual cues look similar from a distance, up close there are measurable differences. If you had said that they are identical, then you may be accepting any car someone can manufacture with a warranty.
The same can be said of fabricated glass. When looking at a feature glazing area of a building, do you want your clients to perceive a Kia… or a Cadillac. How about a Mercedes? There are many price points within the realm of structural glass that are heavily influenced by the design, back-up structure required, and budget. The quality level, however, must be specified so that you get that Cadillac or Mercedes perception. You get what you pay for in this regard, and it all depends on how you want to differentiate your building from the rest.
Structural glass is used almost exclusively for feature areas of projects where clients want a more transparent look from inside out and outside in. They don’t want large aluminum vertical mullions and horizontals, or additional steel supports coming across to break up spans. It’s an inherently more expensive option due to the face glass and back-up structure doing all of the work as mentioned above. These systems may look similar from a distance at night, but that’s not when most people are viewing these feature areas. Most are looking to utilize the atrium and lobby spaces during business hours. That’s where these transparent structural glass systems really shine.
It needs to be visually appealing, distortion-free as possible, and crisply reflect the surroundings while providing a clear view inside and out. Since these systems use tempered glass for added strength, there will be roller-wave distortion that is inherent in the process. This can be controlled with the proper equipment and processing techniques.
Pilkington Planar™ structural glass at the Beverly Center in Los Angeles, CA (left). Structural glass system with high visual distortion in NJ (right).
The fittings need to be kept as small as possible to minimize detection and should be spread out as far as possible to keep things light. Not all fittings from manufacturers are created equal and not all glass is tempered the same. We generally use ¾” exterior countersunk, flush bolts with the Pilkington Planar™ system to keep the fittings as small and unobtrusive as possible. Others may use larger disks and caps. Each manufacturer has its own design parameters and tolerances to be aware of.
Pilkington Planar™ system with flush countersunk bolt 905 fittings in Manhattan (left). Another structural glass system in Manhattan with spider castings and caps (right).
There is no doubt that there is a difference when it comes to the design and fabrication of standard glass in aluminum curtain wall versus custom tempered structural glass and fittings for point-supported glass systems. That’s why it is always important to discuss your options with a system supplier from the beginning. They can clear up any misconceptions about structural glass early on for your next project, and ensure you are receiving the highest quality product that meets the exact project requirements. If you have any other questions about structural glass systems or are looking for help on starting a project, feel free to contact us and we’d be glad to assist.
W&W Glass LLC is a family owned business with a 70-year history in the metal and glass industry, one of the largest metal and glass companies in the New York metropolitan area and the largest supplier of structural glass systems in the country. We have over two decades of experience in the design and installation of various building enclosure systems, including stick-built curtain walls, pre-glazed unitized curtain walls, Pilkington Planar™ structural glass facades, and custom metal and glass enclosure systems. We install all of our work with our own dedicated union labor force. W&W is consistently the largest employer of glaziers in the NY metropolitan area.
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