If you have ever wondered why some homes feel noticeably warmer in winter without the heating working overtime, the answer is often in the glass. A low emissivity glass skylight is one of the most effective upgrades a homeowner can make, delivering better thermal performance, reduced energy bills, and a far more comfortable living environment during the colder months. Understanding how this technology works can help you make a smarter, longer-lasting decision when choosing or upgrading your skylights.
In this guide, we explain exactly what Low-E coatings are, how they function in a low emissivity glass skylight, and why they matter so much when temperatures drop across the UK.
What Is Low Emissivity Glass?
Emissivity refers to a material's ability to emit thermal energy. Standard glass has a high emissivity rating, meaning it radiates heat out through the surface relatively easily. Low emissivity (Low-E) glass is treated with an ultra-thin metallic coating that significantly reduces this heat transfer, keeping warmth inside your home rather than letting it escape through the glazing.
The coating is invisible to the naked eye and does not obstruct natural light in any meaningful way. It is applied during the manufacturing process to the inner surface of the glazing unit, where it acts as a thermal barrier. Think of it like a one-way thermal mirror: it allows solar energy in but resists heat from passing back out.
How Low-E Glass Works: The Science in Simple Terms
There are two main types of Low-E coatings used in modern skylight manufacturing:
Hard coat (pyrolytic) Low-E: Applied during the float glass process whilst the glass is still hot. This creates a more durable coating, though it is slightly less thermally efficient than soft coat.
Soft coat (magnetron sputtered) Low-E: Applied after the glass has cooled in a vacuum chamber. It offers superior thermal performance and is the most commonly used type in premium insulated glazing units (IGUs).
To understand why this matters for skylights specifically, consider that heat rises. Your roof glazing is directly in the path of warm air that accumulates at ceiling level. Without Low-E glass, a significant portion of that heat passes straight through the glass and is lost to the outside. With a Low-E coating, the process is reversed, and the warmth stays inside.
Low Emissivity Glass Skylight vs Standard Glass: A Clear Comparison
The difference in real-world performance between a low emissivity glass skylight and a standard glazed unit is significant. The table below outlines the key differences homeowners should be aware of:
|
Feature |
Low-E Glass Skylight |
Standard Glass Skylight |
|
Heat Retention |
Excellent – reflects heat back in |
Poor – heat escapes easily |
|
U-Value (typical) |
0.9 – 1.2 W/m²K |
2.6 – 5.0 W/m²K |
|
Winter Comfort |
High – reduces cold spots |
Low – draughts common |
|
Energy Bills |
Lower – less heating required |
Higher – more heat loss |
|
UV Protection |
Yes – coated to reduce UV |
Minimal or none |
|
Condensation Risk |
Reduced |
Higher |
|
Long-Term Savings |
Significant |
Limited |
You can explore our flat roof skylights and fixed roof windows, many of which incorporate Low-E glazing as standard.
How a Low Emissivity Glass Skylight Helps Keep Your Room Warm?
The mechanism behind keeping a room warm with Low-E glass comes down to three key processes working together:
Infrared Heat Reflection
Your boiler, radiators, and even your own body all emit infrared radiation. Without Low-E coatings, this energy is absorbed by the glass and re-emitted outwards, effectively draining warmth from the room. The metallic coating reflects this infrared energy back into the living space, maintaining a more consistent indoor temperature.
Reduced Conductive Heat Loss
Low-E glass is typically used as part of a double or triple glazed unit, often with an argon or krypton gas fill between the panes. This combination drastically reduces conductive heat loss - the transfer of warmth directly through the material. The result is a warmer pane on the interior surface, which also helps reduce condensation.
If you are considering upgrading your roof glazing, our blog on triple glazing vs double glazing for skylights explores how each option performs in terms of insulation and long-term cost savings.
Solar Gain Without Overheating
Low-E coatings are designed to be selective. They allow short-wave solar radiation (visible light and passive solar heat) to pass through during daylight hours, which naturally warms your interior. At the same time, they prevent long-wave heat from escaping at night. This balance of solar gain and heat retention is particularly useful in the UK, where winters are cold but also often accompanied by short periods of useful winter sunshine.
Why Low-E Skylights Matter Particularly for UK Homes?
The UK's climate is uniquely demanding on glazed roof installations. Prolonged cold spells from October through to March mean that poorly insulated skylights can account for a disproportionate share of a home's heat loss. According to building performance data, roof glazing can account for up to 25% more heat loss per square metre than a well-insulated solid roof section - unless fitted with appropriate Low-E glazing technology.
For homeowners looking to improve comfort and reduce heating bills, a low emissivity glass skylight is not simply a luxury feature; it is a practical, cost-effective investment.
For homeowners interested in sustainability, our blog on how skylights contribute to energy savings explores the broader environmental and financial benefits of choosing energy-efficient roof glazing.
What to Look for When Choosing a Low-E Skylight?
Not all Low-E skylights are equal. When reviewing options, look for the following:
U-value: The lower, the better. Aim for 1.2 W/m²K or below for strong thermal performance.
Gas fill: Argon is standard; krypton offers slightly superior performance in narrower units.
Number of panes: Double glazed units with Low-E perform well; triple glazed with Low-E coatings are the highest performers.
Frame quality: A thermally broken aluminium frame prevents the frame itself from becoming a weak point in insulation.
Certifications: Look for BBA or Secured by Design certified products to ensure compliance with UK Building Regulations.
All products in our range meet or exceed UK Building Regulations for thermal performance. If you are unsure which specification suits your home, our team is happy to advise.
