How Long Can I Expect Double Glazing to Last?

Double glazing is designed to be a long-term improvement to your home, but like most building products, it won't necessarily last forever.

So, how long does double glazing last, how can you tell when it is beginning to fail, and does a problem mean you need completely new windows?

The good news is that quality double glazing can provide many years of service when it is manufactured correctly, professionally installed and appropriately maintained. And if you already have aluminium joinery, a problem with the glass doesn't necessarily mean replacing the complete window.

At Ryan Double Glazing, we specialise in retrofitting double glazing into existing aluminium windows and doors throughout Tauranga, Mount Maunganui, Papamoa, the Bay of Plenty, Waikato and Coromandel.

Here's what homeowners should know about the lifespan of double glazing.

What Is the Lifespan of Double Glazing?

There isn't one exact lifespan that applies to every double glazed window.

How long an insulating glass unit lasts can be influenced by the quality of its manufacture, installation, exposure to weather, drainage around the unit and how well the windows are maintained.

The sealed glass unit itself is particularly important. Double glazing consists of two panes separated by a sealed cavity. Maintaining that seal is essential to the window continuing to perform as intended.

New Zealand's Building Code framework specifically addresses the durability of insulating glass units, reinforcing why appropriate materials, manufacture and installation matter.

Rather than judging double glazing purely by its age, homeowners should therefore pay attention to how the glazing is performing.

How Do You Know if Double Glazing Has Failed?

One of the most obvious signs is misting, fogging or condensation between the two panes of glass.

This is different from condensation appearing on the room-facing surface of a window.

A double glazed unit contains a sealed space between its panes. If moisture is appearing inside that sealed cavity, it can indicate that moisture has entered the unit.

Consumer NZ notes that misting or clouding inside an insulating glass unit is likely to mean water has entered between the panes.

Other signs worth investigating can include:

• Persistent cloudiness between the panes

• Visible moisture inside the sealed unit

• Damage around seals

• Cracks or chips in the glass

• Draughts around the window

• Water leakage

• A noticeable deterioration in thermal comfort

Not every one of these symptoms means the double glazed unit itself has failed, so having the window assessed is preferable to assuming it needs replacing.

Why Is There Condensation Between My Double Glazed Windows?

This is an important distinction because not all window condensation means the same thing.

Condensation on the inside surface of your window is generally related to indoor humidity meeting a cold surface. Double glazing can substantially reduce this because the interior pane remains warmer than basic single glazing. Ryan Double Glazing has covered this type of household condensation extensively in previous articles.

Condensation between the two panes, however, is different.

Because you can't simply wipe it away, moisture between the panes can be an indication that the sealed insulating glass unit is no longer functioning as intended.

A useful rule of thumb is:

Water on the room-facing surface = household condensation issue.

Misting or moisture trapped between the panes = have the glazing unit checked.

That distinction can help homeowners identify what type of problem they're actually dealing with.

What Causes Double Glazing Seals to Fail?

A sealed glass unit has to cope with years of changing temperatures and environmental conditions.

Potential factors affecting longevity include installation quality, water management and drainage, physical damage and deterioration of components over time.

Here in the Bay of Plenty, coastal conditions are another reason regular window maintenance matters. Salt and other environmental contaminants can accumulate on aluminium joinery and hardware.

Ryan Double Glazing recommends regularly checking windows for problems such as cracking, splitting or damage around seals and cleaning the windows and frames periodically.

Good maintenance won't make a glass unit last indefinitely, but looking after the surrounding joinery and identifying problems early can help protect your investment.

Does Foggy Double Glazing Need Replacing?

If the fogging is genuinely between the panes, the insulating glass unit should be assessed.

The key point for homeowners is that this doesn't automatically mean the entire window needs to be removed from the house.

Depending on the condition and construction of the existing joinery, it may be possible to address the glazing rather than replace the complete frame.

This is particularly relevant to homes with existing aluminium windows.

Can You Replace Just the Glass in Double Glazed Windows?

In many situations, yes.

The glass and the aluminium window frame are separate components.

This principle is actually central to retrofit double glazing. Ryan Double Glazing upgrades suitable existing aluminium joinery by removing the old glazing and installing new sealed double glazed units rather than unnecessarily replacing the complete aluminium window.

Therefore, if a double glazed unit eventually needs replacing, don't automatically assume you're facing the expense and disruption of replacing the entire window.

The existing joinery first needs to be assessed to determine its condition and suitability.

Do You Have to Replace the Window Frame When Double Glazing Fails?

Not necessarily.

This is one of the biggest misconceptions surrounding window upgrades.

If the aluminium joinery remains in suitable condition, replacing the glass unit can be very different from undertaking a complete window replacement.

Ryan Double Glazing specialises specifically in retaining suitable existing aluminium joinery and installing double glazed units into it.

That can make upgrading older aluminium windows considerably less disruptive than homeowners sometimes expect.

Can Old Double Glazing Become Less Effective?

Double glazing relies on several components working together.

The two panes, sealed cavity, spacer system and seals all contribute to the performance of an insulating glass unit. If that sealed system becomes compromised, its performance may no longer be what it was originally designed to provide.

However, age alone isn't evidence that your double glazing has failed.

If your windows remain clear between the panes, the units are intact and you're not experiencing obvious problems, there may be no reason to replace them simply because they've reached a particular age.

Condition and performance are more useful indicators than the calendar alone.

Can Failed Double Glazing Be Repaired?

This depends on what has failed.

Problems with window hardware, drainage, seals around the joinery or other components may require a different solution from a failed sealed glass unit.

Where moisture has penetrated between the panes of an insulating glass unit, the unit itself may need replacing.

That's why an inspection is worthwhile. It allows the cause of the problem to be identified before deciding what work is actually required.

How Can You Help Double Glazing Last Longer?

Double glazed windows don't require complicated maintenance, but looking after them makes sense.

Ryan Double Glazing recommends regular cleaning of the glass and frames and periodically inspecting the windows for damage. Its existing maintenance guidance recommends cleaning approximately every three to six months and keeping an eye out for damaged seals, glass chips, cracks, drainage issues and other deterioration.

For homeowners, some simple habits can help:

Keep glass and frames clean.

• Keep drainage paths clear.

• Check seals when cleaning your windows.

• Don't ignore cracks or chips.

• Investigate unexpected water leakage.

• Have unexplained misting between panes checked.

• Address problems early rather than allowing them to deteriorate.

This is particularly worthwhile for homes exposed to coastal conditions around Tauranga, Mount Maunganui and Papamoa.

Should I Replace Old Single Glazing Before It Fails?

Single glazing is slightly different because there isn't a sealed insulating unit to "fail" in the same way.

The question instead becomes whether your existing windows are providing the comfort and thermal performance you want.

If your home has older single-glazed aluminium windows and you're experiencing cold rooms, significant heat loss or regular condensation, you don't necessarily have to wait until something breaks before considering an upgrade.

Suitable aluminium joinery can often be retrofitted with double glazing while retaining the existing frames. Ryan Double Glazing's Tauranga service, for example, is specifically based around replacing single panes with sealed double glazed units in suitable existing aluminium joinery.

Is It Worth Replacing Old Double Glazing?

If a sealed unit has genuinely failed, replacing it can restore the benefits that the glazing was intended to provide.

But there's no reason to replace functioning double glazing simply because it is old.

A professional assessment can determine whether the problem lies with the glass unit, seals, hardware, drainage, joinery or something else.

It's also an opportunity to discuss whether newer glazing technology could offer advantages if replacement is required.

Need Your Existing Windows Assessed?

If you've noticed fogging between panes, damaged glazing or other problems with your windows, Ryan Double Glazing can help determine what's happening.

We specialise in retrofit double glazing for existing aluminium windows and doors and work with homeowners throughout Tauranga, Mount Maunganui, Papamoa, the wider Bay of Plenty, Hamilton, Cambridge, Matamata and the Coromandel.

Whether you currently have single glazing that you'd like to upgrade or you're unsure about the condition of your existing glazing, talk to our team about the options available for your home.

Frequently Asked Questions

How long should double glazing last?

There is no single lifespan that applies to every double glazed unit. Longevity depends on factors including product quality, installation, environmental exposure, drainage and maintenance. Condition and performance are better indicators than age alone.

How can I tell if my double glazing has failed?

Misting, fogging or moisture trapped between the two panes is one of the clearest warning signs and should be investigated. Consumer NZ says misting or clouding inside an insulating glass unit is likely to indicate that water has entered between the panes.

Is condensation between double glazing normal?

No. Condensation on the exposed room-side surface can occur because of indoor humidity, but moisture trapped inside the sealed cavity between the panes can indicate a problem with the insulating glass unit.

Why has my double glazing gone cloudy?

If the cloudiness is between the panes and can't be wiped from either surface, moisture may have entered the sealed unit. The glazing should be assessed to establish the cause.

Can you replace double glazing without replacing the frames?

Often, yes, provided the existing joinery is suitable. Double glazed glass units and window frames are separate components, which is why existing aluminium joinery can often be retrofitted rather than completely replaced.

Does failed double glazing need to be replaced immediately?

It depends on the problem. A failed sealed unit may require replacement, while other symptoms can originate from hardware, drainage or joinery issues. An assessment can establish what actually needs attention.

Can double glazing lose its effectiveness over time?

If the sealed insulating glass unit becomes compromised, it may no longer perform as originally intended. However, old double glazing shouldn't be assumed to have failed purely because of its age.

What does blown double glazing mean?

"Blown double glazing" is a common term used to describe a double glazed unit where the seal has been compromised, often resulting in misting or condensation appearing between the panes.

Can misted double glazing be fixed?

The appropriate solution depends on why the unit is misting. If moisture has entered the sealed cavity because the insulating glass unit has failed, replacement of the glass unit may be required rather than replacement of the entire window.

Should I replace 20-year-old double glazing?

Not solely because it is 20 years old. If the glazing remains clear, intact and performs satisfactorily, age by itself isn't necessarily a reason for replacement. If you're seeing misting between panes, damage or deterioration in performance, have it assessed.

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