So, Why Should I Get Double Glazing?

If your home still has single glazing, yes. Double glazing will make it warmer, quieter and far less prone to condensation, and it is the most noticeable comfort upgrade most people make to an older property. If you already have double glazing that is under about fifteen years old, opens and closes properly and shows no misting between the panes, the honest answer is probably not, at least not on energy savings alone.

That distinction matters, because almost everything written about double glazing assumes you are starting from single. The Energy Saving Trust puts the saving from replacing an entirely single glazed semi-detached home with A-rated double glazing at around £140 a year in Great Britain, alongside a cut of roughly 380kg of CO2, against a typical cost of about £12,000 for a full set. That is not a payback story. It is a comfort, condensation and noise story with a modest bill reduction attached. From working with clients across Epsom, Cobham and Esher, we’ve found the homeowners happiest a year later are the ones who wanted a warmer, quieter house. The ones sold a return on investment tend to be the ones still doing the maths.

What double glazing actually changes

A double glazed unit is two panes separated by a spacer bar, with the cavity filled with air or argon, and usually one internal surface carrying a low emissivity coating that reflects heat back into the room. Single glazing sits at roughly 5 W/m²K. A modern double glazed window is typically between 1.2 and 1.4.

Four things change when old windows come out.

• Heat loss drops, partly through better glass and partly through a properly sealed frame.
• Draughts stop, and this is the change people notice first.
• Condensation on the inside of the glass reduces, because the inner pane sits closer to room temperature.
• Noise softens, though it is rarely eliminated.

We’ve found draughts do more damage to how a room feels than the glass ever does. On the 1930s semis common around Ashtead, Banstead and Tadworth, the complaint that brings us out is almost always one cold room, and the cause is usually air leaking around a tired frame rather than heat escaping through the pane. Seal that properly and the room changes character before the glazing specification has done anything at all.

When double glazing is not the right call

There is a version of this decision where the answer is no, and it is worth saying plainly.

If your existing double glazing is intact, the seals are sound and there is no misting between the panes, replacing it will not transform your bills. Swapping older double glazing for new double glazing is a marginal thermal gain, not a step change. The reason to do it is usually something else, such as rotten timber, failed hinges, poor security, or a house that simply looks tired.

Misting between the panes is the clearest signal that a unit has genuinely failed, because it means the seal has gone and the cavity is no longer doing its job. Difficulty locking, visible frame decay and draughts you can feel with a hand are the others.

Double glazing or triple glazing

This comes up on most quotes. In our experience, a high specification A-rated double glazed unit works better than triple glazing for the majority of Surrey retrofits, because the third pane adds weight and depth that existing openings and frames were never designed to carry, while the thermal gain over a good double unit is small enough that most homeowners never actually feel it. The Energy Saving Trust puts triple glazing at around 20% more expensive than double.

Triple glazing earns its place in specific situations. New builds designed around it, homes on genuinely loud roads, and properties targeting very low energy use. It is a considered choice rather than a default upgrade, and the difference between double and triple glazing is worth understanding before you pay for the third pane.

What actually decides how well a window performs

The badge on the glass is only one input. The whole window is what gets rated, and the U value you are quoted should cover frame and glass together, not the centre pane in isolation. Beyond that, four details do the real work.

• Warm edge spacers rather than aluminium, which reduce cold bridging at the perimeter of the unit.
• Argon fill in the cavity, which insulates better than air.
• Low-E coating on an internal surface.
• Frame material and thermal break quality, which varies enormously between systems.

We’ve found the installation matters more than the specification sheet. A 1.2 W/m²K window fitted with poor packing, unsealed reveals and no attention to the perimeter will underperform a 1.4 unit fitted properly, every time. This is the part no brochure covers and the part that decides whether you feel the difference.

The systems we fit reflect that. Rehau and Liniar for uPVC, Smart Systems and Origin for aluminium, and The Residence Collection where a period frontage needs a timber look with modern performance.

The rules you cannot ignore

In England, replacement windows in an existing home must achieve a whole window U value no worse than 1.4 W/m²K, or a Window Energy Rating of band B as a minimum, under Approved Document L. Your new windows also cannot be worse than the ones they replace.

Because modern windows are more airtight than what they replace, ventilation has to be considered too. This is why trickle vents appear on most replacement schemes.

The work is notifiable. Either your installer is registered with a competent person scheme and self certifies, or you apply for building control approval yourself. Skyway Windows is FENSA registered under number 41110, which means the certificate is issued directly and the compliance paperwork is handled without you touching it. That certificate matters later, because a buyer’s solicitor will ask for it.

How long it should last

Well made, well fitted double glazing lasts 20 to 35 years, and often longer with maintenance. That figure is doing a lot of work though. The gap between a unit that lasts 20 years and one that lasts 35 is rarely the glass. It is the quality of the seal, the frame and the fitting.

Period properties and conservation areas

Much of the housing stock we work on across Surrey is Victorian, Edwardian or interwar, and some of it sits in conservation areas or under an Article 4 Direction. Neither automatically rules out double glazing, but it does change what you can specify.

Where the original windows were timber, slim profile double glazed sash windows or flush casements usually satisfy both the conservation officer and the performance requirement. Listed buildings are a separate conversation and need consent. If you are unsure, the local council’s conservation officer is the first call, before any quotes.

So, should you get double glazing?

Work through it honestly.

• Single glazing anywhere? Yes, and start with the coldest rooms if budget is staged.
• Misting, draughts, rot or locks that fight you? Yes, on condition rather than efficiency.
• Sound double glazing under fifteen years old? Probably not, unless appearance or security is driving it.
• Chasing a payback figure? Reset the expectation. Windows are a comfort upgrade with a bill benefit, not an investment.

If you want a straight assessment of what your windows are actually doing, rather than a sales pitch, get in touch and we will tell you if replacing them is worth it.