There is a plethora of glazing options available, and Wisconsin Solar Design provides many.
Insulated glass is a sandwich of two or more glass lites, separated by interspaces, and with sealed perimeter spacer assemblies. Monolithic glass is either a single glass pane or multiple panes laminated together, without insulating interspaces. Structured polycarbonate panel glazing is a translucent thermoplastic, extruded at various thicknesses with many layers of insulating air pockets. Plastic domes are solid sheets of acrylic of polycarbonate, formed into a dome or pyramid profile, and often paired together with an insulating air space between.
WSD’s metal-framed skylights, sloped glazing, solariums, and greenhouses - enclosing climate-controlled interior spaces - use either insulated glass or structured polycarbonate panel glazing. This is usually captured within a rafter and bar cap system, but glass can also employ structural silicone glazing adhesive and structured polycarbonate can have standing seam and batten joints at overhead, sloped locations.
Our canopies – over outdoor spaces – typically employ either monolithic laminated glass or structured polycarbonate panel glazing, in one of several different systems. Since glazed canopies are usually supported by a structure of steel or wood, they can use standard rafters or a more minimal extrusion beneath them. Topside, bar cap can be used at joints, in the direction of the canopy’s pitch, or glass joints can utilize structural silicone glazing adhesive. Alternatively, structured polycarbonate panel glazing can be provided with standing seam and batten joints (aligning with canopy pitch), and the whole system is clipped directly to the steel/wood structure. Another option is point-supported-glass (PSG): metal “spider” fittings are mounted to the steel/wood structure and fit through coordinated holes in the laminated monolithic glass, clamping it in place; the flush joints in the glass are then filled with sealant. Point-supported-glass fittings are typically mounted beneath the glass, but can also be placed above the canopy, suspending the glass.
Pre-assembled and glazed unit skylights, available for smaller openings (8’ x 8’ or smaller), can either be smaller versions of our metal-framed skylights, or be plastic dome unit skylights. Our metal-framed unit skylights use glass or structured polycarbonate panel glazing (standard, no standing seams) in our standard framing, as detailed above. Plastic unit skylights utilize domes of solid acrylic or polycarbonate, captured in an aluminum retaining ring at the perimeter. Plastic unit skylights almost always are double dome, as the air space between the two domes provides additional insulation for interior spaces.
WSD recommends glass for most applications. Glass offers standard-to-high light/thermal/visual performance, long product life, and a high-grade appearance. There are almost endless options for glass (discussed below) to produce just the performance and aesthetic your project.
When a project budget is tighter, or thermal performance needs to be extremely high, structured polycarbonate panels are a good choice. Structured polycarbonate panel glazing is lower per square foot than glass, yielding a lower upfront cost. Structured polycarbonate panel glazing has an intermediate product life. While there is a lot of overlap with glass in terms of thermal performance, the thickest of WSD’s structured polycarbonate panel glazing has better U-factor numbers than glass.
Projects with a lower budget, or with a large quantity of small openings, might consider unit skylights with solid acrylic or polycarbonate domes. These are on the low end of the spectrum in terms of thermal performance and product life, but are quite cost effective.
Glass options include colored tints, low-iron glass, silk-screened ceramic frits, low emissivity (low-e) coatings, gasses for the interspace, different spacers, translucent/specialty interlayers for laminated glass, etc.
Low-e coatings are the most commonly used option. They can substantially improve the thermal performance of your glass. This is accomplished by reducing conduction between the glass and the adjacent air volume; often, the low-e also reflects much of the infrared light from the sun, reducing radiant heat gain. Depending on your project’s climate and dominant heating/cooling needs, you should start by looking at low-e’s that either minimize (reflect) radiant energy or admit it. From this point, compare low-e options based on U-factor (conduction), SHGC (radiant heat gain), VLT and reflectance (clarity), appearance (some produce a slight coloration, similar to tints), and LSG (light-to-solar gain; a measure of performance). Low-e’s work best on insulated glass, on a surface facing the interspace (usually #2 or #3). Sputtered low-e’s offer better performance, but harder pyrolytic low-e’s are available to exposed interior or exterior surfaces. While some high-performance low-e’s can be a bit costly, most are a small – moderate price increase and provide a lot of bang for your buck.
Glass tints are usually produced by adding small amounts of metal oxides to the glass, producing a slight, integral color with low reflectance. This yields a range of green, blue, bronze, or gray colors. Glass coatings can also provide tints with stronger colors and higher reflectance. Glass tints are more than just aesthetics, though – they can be a very useful tool for controlling solar heat gain. Some tints are commonly stocked, adding a small cost, while others are special order and can add significantly to both cost and lead time.
Standard clear glass is well-suited for most projects, but does have a very slight green coloration (most visible when viewed edge-on). In some applications, such as laminated glass with a translucent white interlayer, the green becomes more pronounced. Sometimes you may want that little bit of extra clarity. Low-iron glass (including brand names like Starphire, UltraClear, etc.) can be used in these situations. It does cost a little more.
Ceramic frits can be applied to glass to produce a pattern, a design, or reduce light transmittance or heat gain. They are available in white, gray, black, or a variety of muted or bright colors. The frit is a mixture of tiny glass particles and pigment that is heated and fused to the glass, creating an extremely durable coating. There are many standard patterns (dots, lines, etc.) with multiple levels of coverage (percentage of glass remaining transparent) – or custom designs can be silk-screened onto the glass. A standard color and pattern/coverage will add a small cost, while custom colors and silk-screen designs can add significant cost.
Insulated glass usually comes with an air-filled interspace, but inert gasses like argon are available, resulting in a small cost and performance increase. There is debate over whether/when inert gasses escape the interspace and the performance boost is lost.
Laminated glass typically comes with a clear PVB (polyvinyl butyral) interlayer. Base colors are available and can be built up to produce different colors/levels of translucency. A single white base interlayer is often used; there are several (differing translucency) to choose from. Other options provide enhanced acoustics, small or large missile / hurricane resistance, blast mitigation, etc. Color and specialty interlayers increase the cost a little.
Insulated glass typically includes a mill/natural finish aluminum perimeter spacer between the glass lites; a black finish color is also available. “Warm edge” spacers increase edge-of-glass and overall thermal performance, along with some additional cost. Stainless steel is less conductive than aluminum. Spacers made of biopolymers or thermoplastics provide even better thermal performance.
Sizing your glazing properly is important; performance and cost implications should be taken into consideration as part of the design. For glass, large units will require thicker glass in order to meet increased loads. Thicker glass costs more in terms of materials, but also because large glass units are heavy enough that they cannot be safely installed by hand. As a very rough rule-of-thumb, insulated glass units over 16 square feet may require a crane and vacuum lifter, with associated cost. Bay widths of 3 – 4 feet are a good starting point for glass. Translucent structured polycarbonate panel glazing is much lighter, and the main consideration is waste. These panels come in 4 foot standard widths (sometimes 6 foot); designing bay widths at or just under these dimensions result in less waste and thus less overall material cost. The panels come in lengths up to 39 feet; take advantage of this to eliminate horizontal joints. Standing seam structured polycarbonate panels have standard widths of 2 feet or 4 feet, with 39 foot lengths.
Lastly, the price of glass is based on a rectangular footprint that captures a unit’s particular shape. Thus, square and rectangular glass units are the most cost efficient. With triangles, polygons, etc., you still pay for the glass that was cut away. Curved edges are a bit more expensive to cut and insulate than straight edges.