Retrofit Double Glazing vs Full Window Replacement

Is retrofit double glazing a better choice than replacing the whole window?

Retrofit double glazing keeps your existing frames and swaps the single pane for a double-glazed unit or sash, so it suits sound timber windows in Adelaide homes you want to keep. Full replacement suits frames that are rotten, draughty or aluminium. As a typical guide, retrofit sashes run $1,800–$4,000 per opening; full double-glazed replacement runs $1,500–$8,500 per opening fitted.

The right answer depends almost entirely on the condition and type of the frame you already have. Glass is only part of how a window performs. If the frame leaks air, rattles or conducts heat freely, a better pane inside it only fixes half the problem. This guide sets out how we weigh the two options on an Adelaide measure.

What retrofit double glazing actually means

“Retrofit” gets used loosely, so it helps to be precise. In practice it covers two approaches:

• New double-glazed units in the existing sashes. The sash is rebated (routed out) so it can hold a thicker insulated glass unit (IGU), then re-glazed and re-hung. This works only where the timber has enough depth and strength to take the extra thickness and weight.
• New double-glazed sashes in the existing frame. The outer frame stays in the wall and new sashes are made to fit it. This is common on timber casement and double-hung windows where the frame is sound but the old sashes are tired.

In both cases the brickwork, render, architraves and window boards stay untouched. That’s the main appeal: less disruption, no making good around the opening, and the original look of the house is kept.

When retrofit makes sense

Retrofit is usually worth considering when:

• The frames are timber and in good condition. No soft rot at the sill, joints still tight, paint holding.
• The house has character worth keeping. Bluestone villas in Unley, Norwood and North Adelaide, or 1920s bungalows with original casements, often look right with their own frames.
• Heritage controls apply. Where a property is a heritage place or sits in a Historic Area or Character Area Overlay, keeping the original frame can make the change simpler. Our guide to replacing windows in heritage and brick homes covers the planning side; your council confirms what needs approval.
• You want less mess. No frame removal means no render or brick patching.

When full replacement is the better call

Full replacement is usually the better option when:

• The frames are aluminium. Aluminium frames generally can’t be retrofitted with double glazing. The sections are too shallow to take a thicker unit, and a standard aluminium frame conducts heat readily regardless of the glass. Replacing with a double-glazed aluminium (ideally thermally broken) or uPVC window is the usual answer.
• The timber is failing. Rotten sills, split joints or sashes that have been patched repeatedly are a poor base for an expensive new glass unit.
• The window style no longer suits the room. If you want an awning instead of a fixed pane, or a bigger opening, that’s a replacement job.
• You want the strongest thermal result. A new frame designed around double glazing seals better than an old frame adapted to it. For west-facing rooms that cook in an Adelaide summer, that difference is noticeable.

For more on frame choice, see aluminium vs uPVC vs timber windows.

Retrofit double glazing cost vs replacement cost

These are typical guide ranges for Adelaide homes, per opening:

Option	Typical range	What it includes
Retrofit double-glazed sashes	$1,800–$4,000 per opening	New or re-glazed sashes in the existing frame
Aluminium double-glazed replacement	$1,800–$5,500 per opening fitted	New frame and glass, removal and making good
uPVC double-glazed replacement	$1,500–$7,500 per opening fitted	New frame and glass, removal and making good
Timber casement double-glazed replacement	$2,800–$8,500 per opening fitted	New timber frame and glass, removal and making good

Notice the overlap. A retrofit isn’t automatically cheaper than replacement. Retrofit work on old timber is often hand work: stripping, repairing joints, rebating, re-hanging and repainting. On a straightforward modern opening, a new uPVC or aluminium double-glazed window can land in a similar range. What retrofit buys you is keeping the original frame, not necessarily a lower price.

The double glazing cost guide goes deeper on what moves the number.

Where secondary glazing fits in

Secondary glazing is a third option that’s often confused with retrofit. Instead of changing the existing glass, a second, separate pane or pane is fitted on the inside of the window, leaving an air gap between it and the original glass. Some systems are fixed, some hinge or slide, and some lightweight panes attach magnetically.

It can help with draughts and noise, and it’s sometimes used where heritage controls rule out touching the original window at all. The trade-offs are that you now have two layers to open and clean, the inner pane changes how the window looks from inside, and it doesn’t fix a frame that leaks or rots.

We don’t install secondary glazing products. We mention it because it’s a legitimate option for some homes, and if it suits yours better than retrofit or replacement, we’d rather you knew. On a measure we focus on replacement windows and retrofit double-glazed sashes where the frame can take them.

How we assess your windows on site

On a measure we look at each opening separately, because the answer is often different from window to window in the same house. We check:

1. Frame material and condition. Probing the sill and lower joints of timber frames for soft spots.
2. Sash depth. Whether there’s enough timber to hold a double-glazed unit without weakening the sash.
3. Operation. Whether sashes open and close properly and whether hardware is serviceable.
4. Orientation and room use. West and north-facing glass and bedrooms usually get priority.
5. Planning context. Heritage overlays, strata rules, or bushfire requirements in the Hills.

A common outcome is a mix: retrofit on the front elevation where the original timber matters, and full replacement on the rear where aluminium sliders were added decades ago. Your written, itemised quote shows each opening and each option so you can choose.

Related services

We quote and install double glazing and replacement windows across Adelaide metro and the Adelaide Hills, including new timber windows and restoration-style work on double-hung windows. We work across the eastern suburbs, the Adelaide CBD and inner suburbs and every other metro region.

Frequently asked questions

Can you retrofit double glazing into aluminium windows?

Generally no. Most residential aluminium frames are too shallow to take a thicker double-glazed unit, and the frame itself conducts heat, so the usual answer is a replacement double-glazed aluminium or uPVC window.

How much does retrofit double glazing cost in Adelaide?

As a typical guide, retrofit double-glazed sashes run $1,800–$4,000 per opening in Adelaide. Size, the condition of the timber, the amount of repair needed and the finish all move the price, and your written quote sets it out per opening.

Is retrofit double glazing as good as new double-glazed windows?

It can perform well where the frame is sound and seals properly, but a new frame designed for double glazing usually seals better. Retrofit is mainly chosen to keep original timber frames and the character they bring.

What is the difference between secondary glazing and retrofit double glazing?

Retrofit double glazing replaces the single pane or sash with an insulated double-glazed unit. Secondary glazing adds a separate inner pane or pane in front of the existing window and leaves the original glass in place.

Do I need council approval to retrofit double glazing?

Often not for like-for-like work, but heritage places, Historic Area or Character Area Overlays and strata rules can change that. Check with your council, PlanSA or your strata manager before work starts.

Can I retrofit some windows and replace others?

Yes, and that mix is common. Many Adelaide homes keep original timber at the front and replace later aluminium windows at the back, and the quote prices each opening separately.

Get a quote

The fastest way to know whether your frames will take a retrofit is to have them looked at. We’ll measure on site, check each frame, and give you a written, itemised quote showing retrofit and replacement options side by side. Request a quote or call 0468 038 136, and we’ll get back to you within 24–48 hours.