Glass options for windows and doors: Low-E, argon, triple and laminated

What is an insulated glass unit?

An insulated glass unit, or IGU, is two or more panes of glass sealed around the edge with a gap between them. It is the standard for exterior windows and doors. The gap slows heat flow. Coatings, gas and the edge spacer tune how well it works.

Jada states the idea simply: “The glass itself has very poor thermal resistance, so the air space is the primary resistance.” Sun Windows says “all Sun products use dual-glazed insulated glass as standard.” Every choice in this guide is a variation on that unit.

The table below sums up the main options. Details follow.

Option	What it does	Trade-off to ask about
Low-E coating	Reflects heat; cuts heat flow and sun heat	Slight tint or color; choose the type for each wall
Argon fill	Slows convection in the gap	Needs a good edge seal to stay in
Triple glazing	Adds a pane and a second gap	More weight, more thickness, higher cost
Warm-edge spacer	Keeps the glass edge warmer	Quality varies by maker
Laminated glass	Bonds panes with a plastic layer; sound and UV	Added thickness and cost
Tempered glass	Heat-treated glass for safety areas	Required in some locations; check code
Oversize glass	Fewer seams, bigger views	Higher cost, weight, possible no warranty

What does Low-E glass do, and which type suits Texas?

Low-E glass has a thin metal coating that reflects heat. It cuts heat gain in summer and heat loss in winter. The Department of Energy says low-e coatings “are effective at reducing summer heat gain and air conditioning costs without significantly impacting visible light or color.”

Coatings come in strengths. Sun, for example, offers a second-generation 270 Low-E that it calls “most effective in mixed hot and cold climates,” and a third-generation 366 Low-E3. The 270 lets through 70% of visible light. More layers of coating generally block more heat, but they can reduce light.

Jada also explains that “Low E glass types can be oriented to reflect heat away from the building or reflect heat back into the living space depending on the environmental need.” For Texas, ask which coating the maker recommends for each wall. West and south walls need the most sun control. See the SHGC and U-factor guide for how to read the results.

One caution. Jada notes that “Low-e coated glass may exhibit a hue or coloration that is not apparent in architectural samples.” Ask for a full-size sample, and view it on site.

Why does argon gas matter?

Argon fill improves insulation without changing how the window looks. It is a heavy, inert gas that replaces air in the gap. Sun explains that filling the space with argon “improves thermal performance by slowing convection currents within the sealed insulated unit.”

The size of the gap also matters. Jada says “testing has shown that the optimum space for air and argon is around 1/2” up to 5/8” between glass panes.” Too little space transfers more heat. Too much space allows air to churn.

Krypton is another gas option, and it suits thin gaps. The Department of Energy lists “argon or krypton gas” among the features that lower U-factor. Ask which gas your maker uses and what the seal warranty covers.

Is triple glazing worth it?

Triple glazing adds a third pane and a second gap. It cuts heat flow further. It also adds weight and thickness, which affects frames, hardware and cost. For many Texas homes, a well-chosen double-pane Low-E unit does the main job.

The Department of Energy shows what triple glazing can reach. Its table for the most efficient model uses “triple-pane, low-emissivity, low visible transmittance, argon windows with a U-value of 0.12 and a solar heat gain coefficient (SHGC) of 0.21.” That model comes from a Minnesota design guide, so it reflects a cold-climate case. It also uses a low visible transmittance, which means a darker view.

Weight is the practical limit. Jada says that for operable openings “the weight and thickness are more of an issue.” A heavy sash needs stronger hardware and can limit how big a door can be. Sun lists a triple-glazed unit with two sealed air spaces as an option. Whatever the brand, ask for the NFRC rating for the double and triple versions of your product, then compare the gain with the added cost and weight.

What is a warm-edge spacer?

A warm-edge spacer is the strip that separates the panes at the edge of the glass. A metal spacer conducts cold and heat. A warm-edge spacer uses less conductive materials, so the glass edge stays warmer. That cuts condensation near the frame.

Jada explains that spacer bars have “been upgraded from a folded aluminum shape to a combination of different thermally resistant materials” and that “use of the thermal spacer bars improve the overall efficiency of the insulated glass unit.” The sample ratings on its energy page use a Technoform TGI spacer.

Sun Windows uses its Duralite spacer in all of its IG units. Sun says it “provides a warmer edge-of-glass temperature which improves the condensation resistance of the IG unit.” When you compare quotes, ask which spacer each maker uses, because it changes the whole-window rating.

Laminated or tempered: which one do I need?

Pick laminated glass for sound and UV control. Pick tempered glass where building rules or safety call for it. Many openings use both in one unit. Ask your builder or code official where safety glazing is required in your plans.

Laminated glass bonds two panes with a plastic layer. Jada says “Laminated glass can inhibit sound and the PVB layer between the glass will block out a high percentage of UV rays.” That helps near a street, a pool deck or art you want to protect from fading.

Tempered glass is heat-treated. Sun lists tempered glass as an option “where required,” and as standard on all Sun doors. Jada’s oversize supplier makes “tempered insulated glass.” Door glass and glass near floors often fall under safety rules. Read the local code, and have your designer mark these areas on the window schedule.

How big can glass get, and what does it cost in warranty?

Very large panes are possible, but they raise cost, weight and risk. Jada says its supplier “can produce tempered insulated glass in very large sizes up to 130 x 300.” It also says most oversize glass is sold without warranty. Know this before you draw a big opening.

Jada sets a warranted limit when it supplies the glass: “the maximum glass size that can be warranted is 60 sq. ft.” It adds that “oversize glass can dramatically affect the overall cost and the warranty of the fenestration on a project.” Sun makes a similar point. A product above its catalog size “is produced without a warranty for the product or any oversized component.”

Large panes also have fewer coating choices. Jada notes that coatings for oversize glass are less plentiful than for normal glass, and that coating choices affect color matching. If one wall must match another, check the match in a sample before ordering.

Jada also installs glass from the inside in normal cases. For oversize glass, it may install from the exterior, using a crane, with stainless steel parts that resist rust.

What should I do about hail?

Hail is a real risk in North Texas. The National Weather Service in Fort Worth says severe storms with large hail “can occur throughout the year, but are most common in the spring months.” One 1995 storm caused “an estimated $2 billion in damages in Tarrant and Dallas counties.”

After a storm, follow the Texas Department of Insurance steps. “File an insurance claim as soon as you can if hail or strong winds damaged your home or car.” Photograph the damage. “Cover broken windows and holes to keep rain out.” “Get more than one bid or repair estimate.”

The department also warns about fraud: “It’s illegal to waive a homeowners deductible under state law.” Avoid contractors who offer to waive yours.

Glass choice and hail resistance are not the same thing. Do not assume a Low-E or laminated unit is rated for hail. Ask each maker for published impact test data for your product. Jada does not publish impact ratings on the pages we reviewed. For product-specific details, see the brand pages for Jada, Bertrand and Sun Windows under our partners.

How perfect should the glass look?

Glass is never flawless, so the industry uses an inspection standard. Jada calls it the 11 foot rule. It treats a flaw as a defect only if you can see it under normal light from 11 feet away, in the center 80% of the pane. Close-up inspection under bright light finds flaws in any glass.

Jada puts it this way: “The industry standard for glass inspection is called the 11 foot rule.” It adds that its guidelines cover “architectural glass that is produced as annealed, tempered, insulated, or laminated.” Jada also says low-e coatings can show a hue “when viewed at a glancing angle,” and that heat-treated glass can distort reflections. Neither is treated as a defect.

Agree on the standard before the glass arrives. Ask the supplier for its written inspection method, and ask what happens if a pane fails. Specialty glass can add risk, because Jada warns that “rare” glass can lead to shops that take less care in cleaning and insulating. Study the supplier, not only the glass type.

How do I choose glass wall by wall?

Choose glass for the sun each wall gets. West and south walls need strong sun control. North walls can use lighter coatings. Shaded or covered walls can favor light. Write one glass type per elevation and record it on the window schedule.

1. List each wall and its sun exposure and shade.
2. Pick a Low-E type for each wall and ask for its SHGC and visible transmittance.
3. Choose the gas, the spacer and the pane count.
4. Mark laminated and tempered areas.
5. Check sizes against the maker’s warranted glass limits.
6. Get a full-size sample and view it in your light.
7. Confirm the written glass warranty.

Next step

Honey Rock Window and Door can help you match glass to each wall of your home. Start with the energy-efficient windows page, then use Start your project or call (214) 484-9982.