Double glazing is about cooling too, not just heating
Much of the marketing around double glazing focuses on winter: keeping heat in, lower bills, warm rooms. That’s all true, but it sells the technology short. Modern double glazing does just as much work in summer, keeping unwanted heat out of south and west-facing rooms. If your upstairs bedrooms are unbearable in July, the glazing is often a bigger factor than the loft insulation.
Across our windows range every product carries A-rated glazing as standard. But within ‘A-rated’ there are meaningful choices, particularly around solar control, that determine how the room actually feels in summer.
Our casement windows range offers the same glazing options as the rest of the line-up, so the choice between window style and glazing performance is separate.
The same applies to tilt and turn windows — a popular alternative for upper floors and bathrooms — where the glazing spec is independent of the opening configuration.
What U-values and g-values actually mean
Two numbers tell you how a window behaves: the U-value and the g-value. The U-value measures how much heat passes through the window from warm side to cold side — lower is better. A modern A-rated window typically sits at a U-value of around 1.2-1.4 W/m²K, compared to 5.0+ for single glazing. That’s the headline number that drives winter performance.
The g-value (or solar factor) measures how much solar energy passes through the glass into the room — lower is better for summer comfort, higher is better for winter passive solar gain. Standard double glazing has a g-value around 0.6, meaning 60% of the sun’s energy gets through. Solar-control glass drops that to around 0.3-0.4 without significantly reducing visible light. The BFRC energy rating on every window summarises both factors into a simple A++ to E scale.
Solar-control glass: when it earns its place
Solar-control glass costs slightly more than standard A-rated glazing but the difference in summer comfort on south or west-facing windows is significant. Independent guidance from the Energy Saving Trust on windows covers the basics of solar gain and how to think about g-values alongside U-values.
The practical rule of thumb: solar-control glass is worth specifying on south-facing windows in any room that gets warm enough to be uncomfortable in summer, on west-facing windows in rooms used in the evening, and on any conservatory or orangery roof. North-facing windows rarely benefit. East-facing depends on whether the room is used in the morning.
Argon, krypton and the cavity gases
Modern double-glazed units are filled with argon gas rather than air. Argon is denser, conducts heat less, and improves U-values by around 0.2 W/m²K compared to air-filled units. It costs almost nothing extra and is now standard across virtually all reputable manufacturers — but it’s worth confirming the spec on any quote you receive.
Krypton gas performs slightly better than argon and is sometimes used in triple glazing or in narrow-cavity units where argon doesn’t fit. For most homes, argon-filled is the right balance of performance and cost. Triple glazing has its place but the marginal benefit in our climate rarely justifies the cost for retrofit.
The role of the frame and the seal
Glazing performance is half the story. The frame and the seal around the glass do the rest. Modern uPVC frames with multi-chamber profiles are warmer than they look and continue to improve generation by generation. Aluminium frames need thermal breaks to perform — quality aluminium systems carry polyamide breaks that match uPVC for thermal performance.
The seal between the glass and the frame, and between opening sashes and the fixed frame, controls air leakage. A well-sealed window stops draughts in winter and prevents warm air from bleeding in during summer. Make sure the installer is FENSA-registered so the Building Regulations side is properly handled and the installation detailing is signed off.
Replacing windows for summer comfort: timing and cost
A typical whole-house window replacement takes between two and five working days depending on the size of the property. Most Staffordshire semis run two or three days; larger detached homes run four or five. We protect floors and furniture, take out the old units, fit the new ones, and seal and finish each opening before moving on.
Costs vary widely with property size, window count, frame material and glass spec. A standard semi-detached three-bedroom home typically falls in the £6,000-£12,000 range for full A-rated replacement with solar-control glass on south-facing elevations. We quote at survey, in writing, with no high-pressure follow-up calls.
Frequently Asked Questions
Will new windows make my house cooler in summer?
Yes, particularly on south and west-facing elevations. Solar-control glass blocks a meaningful share of solar heat while letting visible light through. The effect is most noticeable in upstairs bedrooms and conservatories.
Is triple glazing worth it in the UK?
For most UK homes, the marginal benefit of triple over double glazing doesn’t justify the extra cost. It can make sense on extremely exposed sites or for new-builds aiming for Passivhaus standards. For a typical Staffordshire retrofit, A-rated double glazing with the right glass spec is usually the better answer.
How long do A-rated windows last?
Quality A-rated uPVC windows typically last 25-35 years with minimal maintenance. The glass units themselves are guaranteed for 10-15 years against seal failure (the cause of misted units).
Can I get solar-control glass in any window style?
Yes — solar-control glass is a glazing option, independent of the window style. You can have it in casement, tilt-and-turn, sash, or aluminium frames.
What’s the BFRC rating and is it the same as the Energy Saving Trust label?
BFRC (British Fenestration Rating Council) runs the standard A++ to E energy rating scheme for windows in the UK. The Energy Saving Trust Endorsed label is separate but uses similar criteria. Either is a credible indicator of thermal performance.
Next steps
If south-facing rooms are uncomfortable in summer or your bills creep up every winter, your windows are usually a bigger factor than people expect. The next step is a free, no-obligation site visit. Book yours when it suits you.
