Solar Control Glass: When and Why to Specify It
Solar control glass blocks excess solar heat while allowing natural daylight through. This guide explains g-values, the key performance trade-offs, and when to specify solar control glazing in a UK project.
Modern homes and extensions often feature large areas of glazing — generous windows, bifold doors, glazed gables. The same glazing that reduces heating demand in winter can cause serious overheating in summer, particularly on south and west-facing elevations. Solar control glass is designed to manage that trade-off.
What is solar control glass?
Solar control glass has a thin metallic coating that reduces the amount of solar energy passing through the pane as heat. It is measured by its g-value (also called Total Solar Energy Transmittance, or TSET): the lower the g-value, the less solar heat enters the building.
This is separate from the U-value, which measures how well the window retains heat in winter. A well-specified triple-glazed unit for a UK project targets both — a low U-value to minimise heat loss, and an appropriate g-value to control solar gain.
5 benefits of solar control glass
1. Reduces summer overheating
By limiting solar heat gain, solar control glass helps maintain comfortable indoor temperatures without relying on air conditioning. This is increasingly important in the UK, where summer temperatures and south-facing glazed areas are both becoming harder to manage with standard glazing.
2. Maintains natural light
Solar control coatings reduce heat without blocking all visible light. Visible light transmittance (VLT) typically ranges from 30–70% depending on the specification — allowing daylight in while limiting glare and radiant heat.
3. Improves energy efficiency year-round
Reducing the need for cooling in summer complements the insulation benefits of a low U-value in winter. For Passivhaus projects and other low-energy designs, carefully balancing U-value, g-value, and light transmittance is essential to meeting energy targets.
4. Enhances comfort in rooms with large glazing
In rooms with significant south or west-facing glazing — open-plan living areas, glazed extensions, home offices — solar control glass reduces glare and hotspots, making spaces consistently usable throughout the day and across seasons.
5. Works across a range of glass types and finishes
Solar control coatings can be applied to clear, tinted, or low-e glass, and to both double and triple-glazed units. Advanced coatings are near-invisible and maintain the clean sight lines expected in contemporary architecture.
G-value comparison
The table below shows typical g-values across different glazing specifications. The right choice depends on your climate, orientation, and building type.
| Glazing type | Typical g-value | Use case |
|---|---|---|
| Standard double glazing (clear) | 70–80% | Cold climates, passive solar heating |
| Low-e double glazing | 60–70% | Balanced heating and cooling needs |
| Low-e triple glazing | 50–65% | Energy-efficient homes in cooler climates |
| Triple glazing with solar control | 30–45% | Passivhaus, offices, south-facing façades |
| Solar control glass (advanced) | 20–35% | High solar exposure, overheating risk |
The key trade-off
As g-value decreases, glass tends to become darker. The goal for most low-energy projects is to achieve a low U-value and a controlled g-value while keeping visible light transmittance as high as possible. There is no single correct specification — it depends on orientation, room use, and the overall energy strategy for the building.
Nordvest can advise on the right glazing specification for your project. See our solar control glass product page or contact the team to discuss your requirements.