When choosing a rooflight, homeowners often find themselves comparing two main materials: glass and polycarbonate. Both are widely used across the UK, but they perform very differently when it comes to insulation, energy savings, and long-term comfort.
If you are weighing up which type of rooflight is best for your project, this breakdown will help you make an informed decision.
Why Energy Performance Matters in Rooflights
Rooflights are more than just architectural features. They have a direct impact on:
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Heating bills – Poor insulation means heat escapes in winter.
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Summer comfort – Bad glazing leads to overheating.
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Sustainability – Lower energy use means reduced carbon footprint.
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Resale value – Energy-efficient homes are more attractive to buyers.
When choosing between insulated glass rooflights and polycarbonate roof windows, you are essentially deciding how well your home will retain heat and control solar gain.
Understanding U-Values in Skylights
The most important measure of energy performance is the U-value.
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U-value measures how much heat passes through a material.
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The lower the U-value, the better the insulation.
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UK building regulations set maximum U-values for skylights to ensure efficiency.
For context:
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Triple glazed glass rooflights can achieve U-values as low as 0.8 W/m²K.
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Polycarbonate skylights usually sit between 1.8 and 3.0 W/m²K, depending on thickness and layers.
This difference is critical if you want a rooflight that saves energy rather than wastes it.
Glass Rooflights: Technical Performance
Glass rooflights are designed with energy efficiency at the forefront.
Key Features
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Double or triple glazing – Multiple layers reduce heat loss.
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Low-E coatings – Reflect heat back into the home while letting in light.
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Argon or krypton gas fills – Improve insulation between panes.
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Warm edge spacers – Reduce thermal bridging around the edges.
Energy Benefits
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Lower U-values than polycarbonate.
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Better at maintaining stable indoor temperatures.
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Reduced condensation risk due to insulated frames and glazing.
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Longer lifespan, typically 20–30 years, without losing performance.
Polycarbonate Rooflights: Technical Performance
Polycarbonate is a lightweight plastic often used in dome rooflights or industrial buildings.
Key Features
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Multiwall construction – Sheets with internal air chambers for some insulation.
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UV protective coatings – Reduce yellowing and block some harmful rays.
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Lightweight design – Easy to install and cheaper upfront.
Energy Limitations
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Higher U-values, meaning poorer insulation compared to glass.
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Loses clarity over time, affecting light transmission.
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Shorter lifespan, often 10–15 years before replacement is needed.
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More prone to scratches, which affect light quality.
Comparing Glass vs Polycarbonate Skylights in the UK
Here is a direct comparison of how each performs in real UK homes.
1. Thermal Insulation
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Glass skylights with triple glazing outperform polycarbonate in U-value ratings.
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Polycarbonate struggles to meet the same insulation standards.
2. Solar Control
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Glass allows for coatings that block excessive solar gain, preventing overheating.
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Polycarbonate offers less control, which can lead to hot interiors in summer.
3. Light Transmission
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Glass provides crystal clear, natural light.
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Polycarbonate can look cloudy and discolour over time.
4. Noise Reduction
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Glass insulates against outside noise far better than polycarbonate.
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Polycarbonate amplifies rain impact noise, which can be disruptive.
5. Durability
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Glass lasts longer with consistent clarity and performance.
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Polycarbonate is cheaper upfront but degrades faster.
6. Compliance
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Glass rooflights easily meet UK building regulations for thermal efficiency.
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Polycarbonate may struggle to comply in residential settings unless heavily upgraded.
Insulated Glass Rooflights and Modern Homes
The shift towards energy saving skylights is being driven by two main factors:
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Rising energy bills – Homeowners want to cut heat loss.
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Stricter UK building standards – Regulations now demand higher thermal efficiency.
Insulated glass rooflights are the natural solution. They balance aesthetics with performance, ensuring your home stays warm in winter, cool in summer, and compliant with regulations.
Where Polycarbonate Roof Windows Still Work
Although glass is the clear leader for energy performance, polycarbonate still has uses.
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Outbuildings and garages – Where insulation is less critical.
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Industrial settings – Lightweight panels cover large roof spans affordably.
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Temporary structures – Quick to install and replace if needed.
For main living spaces, however, glass skylights are the superior choice.
Long-Term Value vs Upfront Cost
One of the main reasons homeowners consider polycarbonate is cost. Polycarbonate roof windows are usually cheaper to purchase and install than glass.
But the calculation should also include:
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Energy savings over time – Glass rooflights reduce heating costs every winter.
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Replacement cycle – Polycarbonate may need replacing twice in the time glass lasts.
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Home value impact – Buyers increasingly expect modern, efficient glazing.
Over 20 years, insulated glass rooflights almost always prove more cost-effective than polycarbonate.
Key Takeaways
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Glass skylights deliver lower U-values, better insulation, longer lifespan, and superior comfort.
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Polycarbonate skylights are cheaper upfront but fall behind in thermal efficiency and durability.
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For UK homes focused on energy performance, glass is the smarter long-term investment.
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Polycarbonate still works for garages, sheds, or low-budget projects.
Final Thoughts
When comparing glass vs polycarbonate skylights UK, the decision comes down to performance versus price. Polycarbonate may appeal for quick fixes or secondary buildings, but glass rooflights are the clear winner for energy efficiency, comfort, and long-term value.
As homes across the UK push for sustainability and lower running costs, insulated glass rooflights stand out as the smarter investment.
Thinking about upgrading to energy saving skylights? Explore our full range of insulated glass rooflights today and get expert advice on the best option for your home.
