Low-E glass is standard on virtually every commercial building in Florida. But most property owners and developers don't know what it actually does — or why it costs a little more than clear glass. This guide explains it without the technical jargon.
What "Low-E" Means
Low-E stands for low emissivity. Emissivity is a measure of how much heat a surface radiates. A surface with low emissivity reflects heat rather than absorbing and re-radiating it.
The Low-E coating on glass is a microscopically thin metallic layer — you can't see it or feel it. It's measured in nanometers. But it has a significant effect on how the glass handles heat.
Think of it this way. Regular clear glass is like a window screen — it lets almost everything through. Low-E glass is more like a one-way heat mirror. Visible light passes through. Infrared heat (the part that warms things up) gets reflected away.
How It Works in Florida's Climate
In Florida, the big problem is solar heat gain. The sun hits your building's south and west glass all afternoon. Without Low-E, a large portion of that solar energy passes right through the glass and heats up the interior. Your HVAC system runs constantly to compensate.
Low-E coating reflects a significant portion of that solar heat before it enters the building. The interior stays cooler. The AC runs less. Energy bills drop.
Studies show properly specified Low-E glass can reduce solar heat gain by 40 to 70 percent compared to clear glass, depending on the coating type.
Understanding SHGC
SHGC stands for Solar Heat Gain Coefficient. It's the number you'll see on every commercial glazing spec sheet.
SHGC ranges from 0 to 1.
- SHGC of 1.0 = all solar energy passes through
- SHGC of 0.0 = no solar energy passes through
- Clear glass = approximately 0.82 SHGC
- Standard commercial Low-E = 0.20 to 0.35 SHGC
Lower SHGC means less heat entering the building. In Florida, you want low SHGC, especially on south and west exposures.
Understanding U-Factor
U-factor measures how well the glass resists heat flow — not solar heat, but conductive heat transfer. Think of it as the glass's insulation value.
- High U-factor = poor insulation (heat moves through easily)
- Low U-factor = better insulation (heat resists moving through)
- Single pane clear glass = approximately 1.0 U-factor
- Standard commercial IGU with Low-E = 0.24 to 0.35 U-factor
In Florida, U-factor matters less than SHGC because our climate is dominated by solar heat gain, not conductive heat loss. But energy code still sets U-factor requirements, and Low-E coatings help meet them.
Why Florida Energy Code Requires Low-E
Florida Energy Code — which is based on ASHRAE 90.1 — sets maximum SHGC limits for commercial buildings. In most Florida climate zones, commercial glazing must achieve an SHGC of 0.25 or lower on west and south exposures.
Standard clear glass has an SHGC of around 0.82. That's more than three times the allowable limit.
Low-E coating is the standard solution. There's no practical alternative for achieving code-compliant SHGC values on clear glass without some form of coating or film.
If your glazing spec doesn't include Low-E, your project will fail energy code review. The building inspector will flag it. You won't get a certificate of occupancy until it's corrected — which means replacing the glass after installation. This is an expensive mistake. See our guide on Florida building code for commercial windows in 2026 for more on the energy code requirements.
Hard Coat vs. Soft Coat Low-E
There are two main types of Low-E coatings. Understanding the difference helps when reviewing a glazing spec.
Hard Coat Low-E (Pyrolytic)
Applied to the glass during manufacturing while it's still hot. The coating fuses into the glass surface and becomes extremely durable. It can be exposed to air without degrading — so it can be used on single-pane applications.
Hard coat Low-E is less expensive to produce, but it offers lower performance. Typical SHGC values are in the 0.35 to 0.45 range — often not low enough to meet Florida energy code on its own.
Soft Coat Low-E (Sputter Coat)
Applied after manufacturing in a vacuum chamber using a process called magnetron sputtering. The coating is extremely thin and uniform, which gives it better optical clarity and lower SHGC values — typically 0.20 to 0.28.
Soft coat Low-E must be sealed inside an insulating glass unit (IGU). The coating degrades if exposed to air or moisture. This is why commercial IGUs are sealed units — the Low-E coating is on the interior surface of one of the glass panes, protected by the IGU seal.
Almost all commercial glazing in Florida uses soft coat Low-E. It achieves lower SHGC values and better overall performance.
Low-E Coating Positions in an IGU
An IGU has multiple glass surfaces, numbered from outside to inside. The coating position affects performance:
| Position | Location | Primary Effect |
|---|---|---|
| Surface 2 | Inside of outer pane (facing air gap) | Best solar control — reduces SHGC most effectively |
| Surface 3 | Inside of inner pane (facing air gap) | Better winter insulation — reflects interior heat back in |
For Florida's hot climate, Surface 2 placement is typically preferred for maximum solar control. Many manufacturers offer dual-silver or triple-silver coatings at Surface 2 that achieve SHGC values as low as 0.18 to 0.22.
What Low-E Doesn't Do
It's worth clearing up a few misconceptions.
- Low-E doesn't significantly reduce visible light transmission in most commercial coatings. The glass still looks relatively clear. Some coatings have a slight green or blue tint, but modern high-performance coatings are nearly neutral.
- Low-E doesn't block UV completely. It reduces UV transmission significantly — typically 70 to 90 percent — but some UV still passes through. Laminated glass is required if UV protection is the primary goal.
- Low-E doesn't replace impact protection. A Low-E coating has no structural function. Impact-rated glass in Florida uses laminated construction — typically PVB or SGP interlayer — that's separate from the Low-E coating.
When to Specify What
For most Florida commercial projects, the glazing spec should include:
- Soft coat Low-E coating, Surface 2 position
- SHGC of 0.25 or lower (check your specific climate zone requirements)
- U-factor of 0.40 or lower
- Dual-pane IGU minimum (triple-pane for ultra-high-performance applications)
If the project is in Miami-Dade or Broward (HVHZ), the glass also needs a Florida Product Approval — which means the specific glass makeup must be listed on a tested and approved unit. You can't just specify a generic Low-E; you need a specific product with an approved FL PA number.
See our guides on commercial glass types explained and ACG's commercial glazing services for more on selecting the right glass for your project. For Miami-Dade projects, also check our page on commercial glazing in Miami for HVHZ-specific requirements.
Frequently Asked Questions
What does Low-E glass actually do?
Low-E glass has a microscopically thin metallic coating that reflects infrared heat radiation. From outside, radiant heat from the sun hits the glass. The Low-E coating reflects a significant portion of that heat away before it passes through the glass. Inside the building, the coating also reflects heat back in during winter. The result is a more stable interior temperature and lower HVAC load.
Does Florida building code require Low-E glass on commercial buildings?
Yes. Florida Energy Code (based on ASHRAE 90.1) sets maximum SHGC and minimum U-factor requirements for commercial fenestration. In Florida's climate zones, most commercial glazing must meet an SHGC of 0.25 or lower on west and south exposures. Standard clear glass has an SHGC of around 0.82 — far above the allowable limit. Low-E coatings are the standard solution. No Low-E means the project fails energy code, and the building cannot receive a certificate of occupancy.
What is the difference between hard coat and soft coat Low-E glass?
Hard coat Low-E is applied during glass manufacturing while the glass is still hot. It's very durable and can be exposed to air, but it offers lower performance — SHGC typically 0.35 to 0.45. Soft coat Low-E is applied after manufacturing in a vacuum chamber and achieves better performance — SHGC typically 0.20 to 0.28 — but must be sealed inside an insulating glass unit. Almost all commercial glazing in Florida uses soft coat Low-E sealed inside IGUs.