Solar heat gain follows a simple rule: the sun moves, and large glazed areas absorb heat as it passes. As the sun rises in the east, tracks across the south, and settles in the west, every major elevation of a heavily glazed home becomes a new source of warming. When the glass‑to‑wall ratio is high, those big glazed areas take in far more solar energy than the insulated walls. This is particularly true if the glass has a poor g‑value.
Understanding g‑value
The g‑value (solar factor) tells you how much of the sun’s energy passes through the glass.
- Good g‑value (0.20–0.35) blocks a hight level of solar heat
- Poor g‑value (0.60–0.75+) allows significant heat into your home
Modern glazing: Great insulation, Weak solar control
Double and triple glazing are often engineered for winter performance. High U‑values that slow the rate of heat loss from the home. Many modern glazing systems excel at insulation but offer limited solar control, leaving homes vulnerable during heat wave.
Smaller windows can contribute to overheating but priority issue comes from large surfaces of exposed glass. Especially those hit by prolonged sunlight. Roof glazing is the most extreme example. It receives direct solar exposure for long stretches of the day, often from multiple angles, making it one of the biggest contributors to rising indoor temperatures. This
My Professional Guide To This Glass Heavy Home
Understanding The Path Of The Sun
Using websites like www.suncalc.org we can get a great impression of how the sun is affecting our home throughout the day. From sunrise (orange line) to sunset (red line) for a specific day of the year. This helps us understand the key areas that are being affected.
The Key Areas of Priority
Priority glazing depends first on how the home is used. The areas we spend the most time in naturally move to the top of the list. From there, the focus shifts to large glazed surfaces on elevations that receive prolonged sunlight, because these sections drive the bulk of solar heat entering the home. When big windows or roof glazing sit in both a high‑use space and a high‑exposure position, they become the primary targets for reducing heat build‑up.
- Key Area 1: W8 Roof Glazing 3000mm x 1700mm
- Key Area 2: S4 3300mm x 3620mm
- Key Area 3: S1 3300mm x 3620mm
- Key Area 4 W8 Side Glazing & ED3 door glazing
- Key Area 5: W2 Front & Side Glazing
- Key Area 6: W12
Recommended Solutions To Key Areas Of Priority
- Area 1: W8 roof – Artemis External Roof Blind £6,230 inclusive of VAT or/& 3M Prestige exterior solar film
- Area 2: S4 – 3M Prestige exterior solar films
- Area 3: S1 – 3M Prestige exterior solar films
- Area 4: W8 and door Glazing – 3M Prestige exterior solar films
- Area 5: W2 Front & Side Glazing – 3M Prestige exterior solar films
- Area 6: W12 3M Prestige exterior solar films
All areas filmed in 3M Prestige 70 or 50 exterior fully installed for £10,450 including access equipment and VAT
For comparison you could opt for Silver 50 Exterior for £4,450 including access equipment and VAT as a compromise.
Marketing Scheme Discount of £300 available.
Artemis External Automated Roof Shading
Stops heat before it enters modern glazing reducing heat gain by over 90% (g-value 0.1)
- Tensioned shading system with no visible cords over the glazing.
- Dimensionally stable fabrics that deliver on performance and aesthetics
- Wind resistance: Up to 24 mph (approx. 38.6 km/h) Beaufort Force 5 (fresh breeze).
- Automated on sun sensors
- Retracts on wind sensor so left unprotected on sunny, windy days
External solar shading can make a major impact on reducing heat gain. The most effective fabrics can cut solar energy by over 90%, giving a g‑value lower than 0.1. This makes roof glazing a smart first target, because it receives prolonged exposure and drives a large portion of the home’s overall heat load.
However when we need to cover extensive glazed areas to improve our homes comfort then 3M Prestige exterior films can be the answer on modern glazing.
3M Prestige Exterior Films
The Prestige Exterior Series blocks over 90% of near‑infrared heat, which is the wavelength that warms every surface it touches. Window cills, flooring, worktops and is the uncomfortable heat we feel when it our skin. Once this short‑wave energy is absorbed, it converts into long‑wave heat and continues to radiate into our living spaces long after the sun has set.
In simple terms it manages this uncomfortable heat whilst focusing less on the visible light spectrum. Visible light does become heat when it builds up in an unventilated space, but that trapped heat can be released quickly by opening a window and allowing airflow.
Success Story Window Film Mark – WindowTreat
| 3M Prestige 90 Exterior | 3M Prestige 70 Exterior | 3M Prestige 50 Exterior | 3M Prestige 40 Exterior | 3M Prestige 20 Exterior | 3M Prestige 70 Interior | |
| Solar Energy Rejection | 21% | 45% | 56% | 59% | 66% | 8% |
| G-Value | 0.48 | 0.36 | 0.26 | 0.24 | 0.19 | 0.54 |
| Light Transmission of Film | 99% | 80% | 57% | 47% | 23% | 78% |
| Exterior Reflection (Daytime) | 13% | 12% | 9% | 7% | 6% | 13% |
| Interior Reflection (Nighttime) | 11% | 14% | 14% | 13% | 12% | 11% |
| UV Rejection | 999% | 99.9% | 99.9% | 99.9% | 99.9% | 99.9% |
Best Solar Control Films for Modern Glazing: 3M Prestige Exterior Compared – WindowTreat
3M Prestige films don’t improve winter insulation, but they do work intelligently with the sun’s position. They are angle‑responsive, meaning they allow more solar warmth into the home during winter when the sun sits low in the sky, and they reject far more heat in summer when the sun is high and intense. This seasonal behaviour gives homeowners the benefit of passive winter gain without sacrificing summer heat protection.
You can consider coupling the internal Solargard Ecolux interior window film for winter comfort whilst allowing the 3M Prestige 70 exterior to manage the solar heat gain on the outer pane. Solargard Ecolux interior film will only provide a 15% solar energy reduction for heat gain despite being great at improving winter comfort.
Combining the two films, 3M Prestige 70 Exterior and Solargard Ecolux Interior will be a light transmission of 44% (similar to 3M Prestige 40 exterior)
Success Story: Anthony’s Ecolux Insulation Upgrade for a Warmer Playroom – WindowTreat
How important is the installation ?
The quality of the installation is just as important as the film itself. The 3M Prestige Exterior Series comes with a 10‑year backed warranty when installed by WindowTreat, and 3M expect a 20‑year life span. But that performance depends entirely on the care taken during fitting. The glazing and framework must be cleaned thoroughly to minimise any risk of contamination under the film. Our visual standards sit above the GGF guidelines, ensuring homeowners feel confident in their investment and receive the finish they expect.
Get in Touch
If you have questions and want to talk through the specifics of your project, our team is here to help. For a friendly chat about the best options for your home, call our specialists.
Call: 01256 345580 or book an appointment online or join Chris on a video chat via his calender below.
