Retrofit vs Replace: What Heritage Homeowners in Melbourne's Inner North Need to Know

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Why Replacement Is the Default (and Why That's a Problem)

Most glazing companies are set up to sell and install new aluminium or uPVC frames. It's a standardised product, easy to quote, and profitable to install at scale. The pitch usually centres on thermal performance and low maintenance — both real benefits, but they come with trade-offs that rarely get mentioned: loss of original joinery and proportions, heritage overlay complications, and a full frame replacement cost that's often higher than restoration.

What Retrofit Actually Involves

Retrofitting means keeping your original timber sash, casement, or awning frames and upgrading them rather than discarding them. In practice this means repairing any rot or damaged joinery, draught-proofing the frame, and fitting double-glazed insulated glass units (IGUs) into the existing sashes where possible. The result is a window that looks unchanged from the street but performs close to a modern double-glazed unit for thermal and acoustic insulation.

Heritage Overlay and Council Considerations

A large portion of Banyule and the surrounding inner-north municipalities sit within heritage overlay zones, which means street-facing window replacement often requires a planning permit — a process that can take months and isn't guaranteed to be approved if the proposed replacement changes the original appearance. Retrofitting, because it preserves the original frame and sightlines, is far more likely to be assessed as exempt or low-impact under these controls. This alone can save homeowners significant time and uncertainty compared to a full replacement application.

Cost Comparison: It's Not as Simple as "Replacement Is Cheaper"

On a per-window basis, a basic aluminium replacement can look cheaper upfront. But that comparison usually doesn't account for the full picture:

• Removal and disposal of original timber frames
• Making good to surrounding plaster, render, or weatherboards
• Potential permit and planning costs in heritage overlay areas
• Loss of resale value associated with original period features

Figures below are general Australian market ranges for planning purposes, not Window Lust quotes for every category — actual pricing depends on product, access, glass specification and installer.

Option	Typical range
Retrofit double glazing, standard sizes	$450 – $900
Retrofit double glazing, double-hungs and custom profiles	$700 – $1,400
Full frame uPVC, standard sizes	$900 – $1,600
Full frame thermally broken aluminium	$1,200 – $2,200

For a typical home with 15 to 20 windows, that works out to roughly:

• Retrofit throughout: $9,000 – $18,000
• Full frame uPVC throughout: $18,000 – $32,000
• Full frame thermally broken aluminium: $24,000 – $44,000

Even before permits, disposal, and making-good costs are added on top of the full-frame options, retrofit comes out ahead across a whole house — and once those extras are factored in, the gap widens further. Restoration and retrofit double glazing is typically the cheaper path overall, while keeping the home's character intact.

Performance: How Close Does Retrofit Get to New Double Glazing?

A well-executed retrofit with quality IGUs and proper draught sealing gets you most of the way to the thermal and acoustic performance of new double glazing, without the downsides of full replacement. The frame itself — timber — is also a naturally better insulator than aluminium, which conducts heat and cold far more readily unless thermally broken (an upgrade that adds further cost to aluminium replacement options).

When Replacement Does Make Sense

Retrofit isn't always possible. If a frame has extensive structural rot beyond economical repair, or the home has no heritage significance and the owner simply wants the lowest-maintenance option regardless of character, replacement may be the more practical choice. A proper on-site assessment is the only reliable way to know which category your windows fall into.