If you have an old polycarbonate dome sitting on your flat roof, you are not alone. Millions of UK homes were fitted with these rooflights during the 1980s, 1990s and early 2000s. They were affordable and quick to install at the time. But fast forward to today, and many of those domes are yellowed, scratched, draughty, and doing very little for your home's energy performance or appearance.
The good news is that you do not need to rip out the whole rooflight from scratch. A retrofit flat glass skylight upgrade lets you replace the dome with a modern, thermally efficient glass unit - often using the existing kerb without major disruption to your roof. If you are ready to replace your dome with glass, this guide covers everything you need to know.
Why Polycarbonate Domes Degrade Over Time
Polycarbonate is not UV-stable in the long term. Even with coatings applied at manufacture, most domes begin to show visible signs of degradation within ten to fifteen years. The dome takes on a yellow or amber tint, fine surface cracks appear, and seals begin to fail - leading to draughts and occasional water ingress. Rain noise through polycarbonate is also noticeably louder than through glass.
From an energy perspective, older polycarbonate units can have U-values of 1.4 to 2.5 W/m²K or worse. That means significant heat loss through your roof every single day of the heating season. An ageing dome is quietly costing you money, reducing your comfort, and making your home look tired from both inside and out.
Polycarbonate Dome vs Flat Glass Rooflight
Before committing to an upgrade, it helps to see exactly what you are gaining. The comparison below covers the most important differences:
| Feature | Polycarbonate Dome | Flat Glass Rooflight |
|---|---|---|
| Clarity | Yellows and hazes over time | Crystal-clear, stays clear for decades |
| Thermal Performance (U-value) | 1.4–2.5 W/m²K (poor) | 0.7–1.1 W/m²K (excellent) |
| Lifespan | 10–15 years typically | 25–30+ years |
| Aesthetics | Bubble profile, dated look | Flat, sleek, modern finish |
| Self-Cleaning Glass | Not available | Available as standard option |
| Maintenance | Prone to algae, hard to clean | Easy to clean, low maintenance |
The difference in thermal performance alone makes a strong case. Replacing a dome with a U-value of 2.0 W/m²K with a double-glazed flat glass unit at 1.0 W/m²K halves the heat loss through that point in your roof.
What the Retrofit Process Generally Involves
Many homeowners assume replacing a skylight means tearing up the roof and starting from scratch. In most cases, that is simply not true. If the existing upstand kerb is structurally sound, it can often be retained or a refurbishment kerb fitted over it, providing a clean base for the new glass unit. The glazing is then installed onto the kerb with a watertight seal, and the surrounding roof membrane is checked and finished properly.
It is a far less disruptive process than a full structural replacement, and in most cases can be completed without major alteration to your roof at all. Our flat glass rooflights can be custom-sized to match your existing aperture, so there is usually no need to modify the roof opening itself.
Choosing the Right Flat Glass Rooflight
Not all flat glass rooflights are the same. When selecting a replacement, there are a few key things to consider.
Glazing type matters most for thermal performance. Double-glazed units with an argon-filled cavity are the standard choice and will comfortably meet current Building Regulations. Triple glazing offers even better performance and is worth considering for bedrooms or living spaces directly below.
Self-cleaning glass is a practical upgrade for any rooflight that is difficult to access. The coating uses UV light and rainfall to break down and wash away organic matter, keeping the glass clear with minimal effort.
Frame colour is largely a personal choice. Powder-coated aluminium frames in anthracite grey or white are the most popular options for UK homes and will complement most roof finishes.
Things to Consider Before You Go Ahead
A retrofit is straightforward in most cases, but there are a few practical points worth thinking through before you commit.
The condition of your existing kerb is the most important factor. If it is sound, the project is simple. If it is rotten or damaged, a refurbishment kerb will be needed — still far less work than a full replacement.
On planning permission: most like-for-like replacements fall within Permitted Development in England and do not require an application. You may need consent if your property is listed, in a conservation area, or if the new unit would sit significantly higher than the existing roofline. It is always worth confirming with your local planning authority before work begins.
From an energy standpoint, switching to double or triple-glazed flat glass can bring your rooflight's U-value well below the 1.6 W/m²K maximum set by Building Regulations Part L for replacement rooflights. You can read more in our guide on choosing eco-friendly skylights for modern UK homes if you want to explore the energy side in more detail.
Why Flat Glass Is the Smarter Long-Term Choice?
The upfront cost of flat glass is higher than a basic polycarbonate dome, but the long-term picture is very different. Glass units last significantly longer, perform far better thermally, require less maintenance, and add genuine value to your home. When you factor in reduced heating bills and the cost of replacing a polycarbonate dome again in ten years, flat glass is almost always the more economical choice over time.
Our dome rooflights range remains available for those wanting a like-for-like replacement, but for most homeowners looking to properly upgrade their rooflight, flat glass is the clear step forward.
If you are ready to explore your options, get in touch with our team or browse our full range of flat glass rooflights online today.
