South-facing glazing is one of the great assets of a Hertfordshire home — flooding kitchens, living rooms, and extensions with natural light throughout the day. But unchecked solar gain can turn that asset into a problem: overheating in summer, glare on screens and surfaces, and increased reliance on air conditioning or mechanical ventilation.
Solar control glass addresses this without sacrificing the transparency that makes architectural glazing worthwhile. By specifying the right coating, you can reduce heat transmission while maintaining the clarity and light levels that define a premium glazing installation.
How solar control glass works
Solar control glass incorporates a microscopically thin metallic or oxide coating applied to one surface of the glass during manufacture. This coating:
- Reflects a portion of solar radiation — reducing the g-value (solar heat gain coefficient) of the glazing unit.
- Filters visible light selectively — maintaining high light transmission while reducing glare.
- Works with low-E coatings — modern units combine solar control with low-emissivity coatings for year-round thermal performance.
The coating is permanent, maintenance-free, and invisible to the naked eye in most specifications.
Key performance metrics
When specifying solar control glass, three metrics matter:
- g-value (solar factor) — the proportion of solar energy transmitted through the glass. Standard double glazing has a g-value of around 0.76. Solar control glass can reduce this to 0.25–0.45 depending on the coating.
- Light transmission (LT) — the percentage of visible light passing through. Premium solar control glass maintains LT of 60–70% while significantly reducing g-value.
- U-value — thermal transmittance for heat loss in winter. Solar control coatings are combined with low-E coatings to achieve U-values of 1.0–1.2 W/m²K.
The goal is to balance solar control with light transmission and thermal performance — not simply to specify the lowest g-value available.
When solar control is essential
We recommend solar control glass for:
- South-facing bi-fold and sliding doors — the most common application in Hertfordshire rear extensions. See our bi-fold and sliding doors service.
- Roof lanterns and glass roofs — overhead glazing receives direct solar radiation for extended periods. Essential for glass roofs and lanterns.
- Large structural glass elevations — full-height glass walls and glass boxes where the glazed area exceeds 25% of the floor area.
- West-facing openings — afternoon sun can cause significant overheating, particularly in open-plan living spaces.
- Conservatory replacements and glazed extensions — where large glazed areas create greenhouse conditions without appropriate specification.
For north-facing openings, solar control is typically unnecessary and may reduce beneficial passive solar gain in winter.
Solar control is not about making glass darker. It is about managing energy transmission while preserving the quality of daylight.
Specifying for different applications
Optimal specification varies by application:
| Application | Recommended g-value | Notes |
|---|---|---|
| Bi-fold doors (south) | 0.30–0.40 | Balance heat rejection with clarity |
| Roof lanterns | 0.25–0.35 | Overhead exposure demands stronger control |
| Structural glass walls | 0.35–0.45 | Large areas; consider external shading too |
| Windows (south) | 0.40–0.55 | Less critical than doors and roofs |
| Windows (north) | Standard low-E | No solar control needed |
We specify glass as part of our bespoke architectural glazing service, selecting coatings from leading manufacturers to match each application.
Combining with other glass technologies
Solar control glass works alongside other specification options:
- Acoustic laminated glass — the laminated interlayer can be combined with solar control coatings for noise reduction near busy Hertfordshire roads.
- Low-iron glass — reduces the green tint in standard glass, maintaining clarity even with solar control coatings applied.
- Self-cleaning coatings — photocatalytic coatings on roof lanterns reduce maintenance on hard-to-reach surfaces.
- Triple glazing — solar control triple glazed units achieve exceptional thermal performance (U-values below 0.8 W/m²K) for high-specification projects.
External shading and solar control
Glass specification is one part of solar management. External shading can complement solar control coatings:
- Overhangs and brise soleil — architectural shading that blocks high-angle summer sun while allowing low-angle winter sun.
- Motorised blinds and awnings — flexible shading for bi-fold and sliding door openings.
- Landscaping — deciduous planting to the south and west provides seasonal shading.
We advise on the balance between glass specification and external shading during your consultation.
Building Regulations and overheating
Approved Document O (Overheating) introduced requirements for limiting solar gain in new residential buildings. While primarily affecting new-builds, the principles apply to large glazed extensions:
- Limit glazed area relative to floor area
- Specify appropriate g-values for orientation
- Consider cross-ventilation and thermal mass
We ensure specifications meet current regulations as part of every structural glass installation and extension glazing project.
Book a consultation
Planning a south-facing glazing installation? Book a glazing consultation and we will advise on solar control specification for your project. Browse our gallery for completed installations across Hertfordshire.
