Bringing daylight into a building through rooflights is one of the most effective design moves available to architects and specifiers. But with natural light comes solar gain and without the right glazing specification, that gain quickly becomes a liability. Solar control skylight glass is the technical solution that allows you to maximise daylight whilst keeping internal temperatures firmly under control.
Whether you are working on a commercial extension, an open-plan office, or a retail environment, understanding how solar control skylight glass performs is essential to specifying rooflights that work year-round.
What Is Solar Control Glass and Why Does It Matter for Rooflights?
Solar control glass is a specialist glazing product engineered to limit the amount of solar energy that passes through the glass whilst maintaining visible light transmission. In a vertical window, this is a useful feature. In a rooflight where the glazing faces the sky directly - it becomes critical.
Rooflights receive a far higher proportion of direct solar radiation than vertical glazing. On a south-facing flat roof in summer, a standard double-glazed unit can allow enough heat into a room to push internal temperatures well beyond comfortable working levels. Air conditioning loads increase, occupant comfort drops, and energy costs climb. Solar control skylight glass addresses this at the source, before heat enters the building envelope at all.
For designers working on commercial schemes subject to Part L of the Building Regulations and CIBSE overheating guidance, solar control glazing is no longer a luxury specification - it is frequently a compliance requirement.
How Solar Control Skylight Glass Works: The Science Behind the Coating
Modern solar control skylight glass relies on thin metallic or metal oxide coatings applied to one or more surfaces of the glass unit. These coatings are selectively engineered: they reflect and absorb infrared radiation (the primary carrier of heat) whilst allowing visible light wavelengths to pass through relatively unimpeded.
The key performance metric is the Total Solar Energy Transmittance, commonly referred to as the g-value or solar factor. A standard double-glazed unit may carry a g-value of around 0.60 to 0.70, meaning 60–70% of incident solar energy enters the space. A high-performance solar control unit can reduce this to 0.20–0.35 - a significant reduction that directly translates to lower peak temperatures and reduced cooling demand.
A second metric, the Light Transmittance (LT), tells you how much visible light passes through. The goal in specification is to achieve a low g-value without sacrificing too much LT. The ratio between the two known as the selectivity index is the clearest measure of how well a glazing product performs in real-world rooflight applications.
Heat-Reducing Skylight Glass: Options Available to Designers
When specifying heat reducing skylight glass for a rooflight project, designers have several glazing categories to consider, each with distinct performance characteristics.
Solar Control Coated Glass
The most widely specified option. A pyrolytic or magnetron-sputtered coating is applied to the inner surface of the outer pane in a double or triple-glazed unit. This reflects solar infrared before it enters the cavity, reducing the g-value substantially. Most commercial rooflights use this approach as the baseline.
Tinted Glazing
Tinted glazing - sometimes called body-tinted or solar-tinted glass incorporates colouring agents within the glass batch itself. Bronze, grey, and blue tints are the most common in rooflight applications. The tint absorbs solar radiation as it passes through the glass, converting it to heat that is then dissipated outward rather than entering the space.
Heat reducing skylight glass in tinted form tends to carry lower visible light transmittance than coated options, which is worth considering when daylighting quality is a priority. However, for applications where glare reduction is equally important - such as south-facing office environments - tinted glazing may offer the better balance.
Combination Units
The most technically capable rooflight glazing units combine a solar control coating with a low-emissivity (low-e) layer. The solar control coating limits summer heat gain; the low-e coating limits winter heat loss. Specifying both within a triple-glazed unit achieves excellent year-round thermal performance without requiring external shading devices.
Solar Control vs. Standard Glazing: Performance Comparison
The table below illustrates how different glazing types compare across the key performance indicators relevant to rooflight specification.
|
Glazing Type |
Typical g-Value |
Light Transmittance |
U-Value (approx.) |
Best Application |
|
Standard Double Glazing |
0.60–0.70 |
78–82% |
2.8–3.0 W/m²K |
Low-solar-risk environments |
|
Solar Control Double Glazed |
0.25–0.40 |
55–72% |
1.2–1.6 W/m²K |
Commercial offices, retail |
|
Tinted Glazing (Bronze/Grey) |
0.35–0.50 |
45–65% |
1.4–1.8 W/m²K |
South-facing rooflights |
|
Triple Glazed Solar Control |
0.20–0.30 |
50–68% |
0.6–0.8 W/m²K |
Passivhaus, net zero schemes |
|
Combination Solar + Low-e |
0.18–0.28 |
48–65% |
0.6–1.0 W/m²K |
Year-round commercial use |
g-values and U-values are indicative and vary by manufacturer and unit configuration.
Glare Control: Beyond Just Heat
Heat and glare are related but distinct problems. A rooflight that controls solar gain may still allow uncomfortable levels of diffuse glare - particularly in working environments where screens are in use.
Glare is measured using the Daylight Glare Probability (DGP) index. For commercial interiors, CIBSE and BREEAM guidance recommend a DGP below 0.35. Tinted glazing and solar control coatings both contribute to glare reduction, but the geometry of the rooflight - its size, position, and orientation also plays a significant role.
For sensitive commercial applications, designers should consider combining solar control glazing on commercial rooflights with a considered layout strategy: positioning units away from primary workstations, or selecting deeper-set kerb profiles that limit the angle of direct sky view.
Specifying Solar Control Glass for Flat Roof Applications
Flat roof rooflights present the most demanding solar control challenge because the glazing faces the sky at a near-horizontal angle for the majority of the day. This is precisely where solar control specification has the highest impact.
When working with flat roof skylights, specifiers should look for products that clearly state the g-value of the included glazing unit. Many entry-level rooflights ship with standard clear glass; the upgrade to solar control glazing is frequently available as a factory option and should be included in the project specification from the outset rather than value-engineered out.
Key specification checklist for flat roof solar control:
- Confirm g-value is below 0.40 for south or west-facing rooflights
- Confirm LT is sufficient for the daylighting strategy (typically above 50%)
- Check that the coating is on the correct surface of the unit (surface 2 or 3 depending on unit configuration)
- Ensure the unit carries the CE marking and meets BS EN 1279 standards for sealed glazing units
Final Thoughts
Solar control glazing is one of the most impactful specification decisions you can make for any rooflight project. It addresses overheating and glare at the source, before they become a problem inside the building. Explore our full range of commercial rooflights to find products specified with solar control glass built in.
