It’s one of the most common calls we receive at Clearglass: ‘My windows have gone misty, do I need all new windows, or can you just replace the glass?’ The good news, in most cases, is that yes, you can replace just the glass unit itself, without touching the frames. This is one of the most cost-effective home improvements you can make, and it’s exactly what we specialise in across Cambridge, Newmarket, Ely and Huntingdon.
But to give you a complete answer, it helps to understand how a double-glazed window is actually constructed — and what causes it to fail in the first place.

How a Double-Glazed Window Is Constructed

A modern double-glazed window has two distinct components: the frame (which might be uPVC, aluminium, timber, or composite) and the glazed unit itself. The glazed unit (also called an insulated glass unit, or IGU) is the sealed assembly of two (or sometimes three) panes of glass with a gap between them. That gap is filled with either air or an inert gas such as argon, which dramatically improves thermal insulation.
Around the perimeter of the unit sits a spacer bar, typically made from aluminium or a ‘warm edge’ composite material. This spacer bar contains a desiccant — a moisture-absorbing material — and is bonded to both panes with a primary and secondary sealant. The whole unit is then fitted into the window frame and held in place with glazing beads and a weatherproof seal.
The key point is this: the unit and the frame are separate components. In most cases, the frame is perfectly sound even when the unit has failed. Replacing the unit means removing the glazing beads, sliding out the old unit, sliding in a new one made to the same dimensions, and refitting the beads. The frame stays exactly where it is.

When Can You Replace Just the Glass?

The vast majority of double glazing failures we see across Cambridgeshire are unit failures — not frame failures. The most common sign is condensation or a misty appearance between the panes, which means the unit’s hermetic seal has broken down, moisture has entered the sealed cavity, and the desiccant is saturated. The glass itself is fine; the seal has just failed.
In these situations, replacing just the unit is absolutely the right approach. There is no benefit to replacing the entire window — the frames are structurally and functionally sound. You get a brand-new, fully sealed, energy-efficient unit fitted into your existing frames, typically in a single visit, at a fraction of the cost of new windows.
This applies across all common frame materials. Whether your home in Cambridge has uPVC, aluminium, or original timber frames, the principle is the same: if the frames are in good condition, only the unit needs replacing.

When Do You Need Full Window Replacement?

There are situations where just replacing the unit isn’t sufficient, and a full window replacement is the better long-term choice:
  • Frame rot or structural failure: timber frames that have significant rot, or uPVC frames that have warped, cracked or lost their structural integrity, need replacement
  • Obsolete frame profiles: very old or unusual frame profiles may mean that finding a correctly sized unit is difficult, or that the frame can no longer adequately hold a new unit
  • Security upgrades: older frames may not meet current security standards; if you’re upgrading for security reasons, full replacement may be more appropriate
  • Significant draughts from the frame: if the frame itself is the source of draughts — not the glazing — replacing the unit alone won’t solve the problem
  • Major cosmetic damage to frames: if frames are badly discoloured, scratched or damaged, and you want a complete visual refresh
A good glazing specialist will be honest with you about which option makes sense for your situation. At Clear Glass, we assess every window before recommending a course of action — and we’ll always tell you if unit replacement alone is the right answer, because we know it saves you significant money.

How Do You Know If Your Frames Are Worth Keeping?

For most homes built or double-glazed in the last 15–25 years, the frames will be uPVC and in perfectly good condition for many more years. uPVC doesn’t rot, doesn’t corrode, and maintains its structural properties for 30–40 years or more. The unit will almost always fail before the frame does.
Timber frames require a slightly different assessment. Original timber-framed double glazing — common in many of the older properties around Ely and Huntingdon — can be excellent, but timber requires maintenance. We look at the condition of the glazing rebate (the channel into which the unit sits), the integrity of any existing putty or sealant, and the overall structural condition of the frame. In many cases, timber frames are perfectly sound and an ideal candidate for unit replacement.
Aluminium frames, common in commercial and some residential properties around Cambridge city centre, are extremely durable and almost always suitable for unit replacement.

What Size Unit Do You Need?

Replacement units are manufactured to measure — not off the shelf. The unit is measured by its overall external dimensions, and the thickness of the spacer bar (which determines the gap between the panes and therefore the unit’s overall depth). Getting this measurement right is critical, and it’s something we cover in detail elsewhere on our blog. As a rule of thumb, always measure the existing unit (if removable) rather than the frame aperture — unit and aperture dimensions are not the same.

How Much Does It Cost to Replace Just the Unit?

Replacing just the glazed unit is significantly cheaper than full window replacement, typically between 20% and 40% of the cost of new windows for an equivalent window. The exact cost depends on the size of the unit, the specification (standard double glazing, low-emissivity glass, argon-filled, acoustic glass, etc.), and the labour involved in fitting. We provide free, no-obligation quotes across Cambridge, Newmarket, Ely and Huntingdon, contact us and we can usually give you a firm price quickly.

Summary

In the large majority of cases, yes, you can replace just the glass. If your frames are sound and your problem is misting, condensation between panes, a broken seal, or simply ageing glass, a replacement double-glazed unit is all you need. It’s faster, cheaper, and far less disruptive than full window replacement, and the result is a window that performs as well as new.
If you’re unsure whether your frames are up to it, give us a call. We cover the whole of Cambridgeshire and are always happy to give you an honest assessment.

Need a replacement double-glazed unit in Cambridge, Newmarket, Ely or Huntingdon? Clearglass offers fast, reliable supply and fitting of replacement double glazed units across Cambridgeshire. Call us today for a free, no-obligation quote.