Double glazed windows

Add value to your home while making it more sustainable in the long term.

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From increasing energy efficiency to adding security, double glazed windows come with all sorts of added benefits for your home. In this guide, we discuss all things double glazing, including its pros and cons, along with some answers to commonly asked questions.

Why should I install double glazed windows?

Double glazed windows are a common feature in most contemporary homes. Windows are the main source of heat loss in buildings, and double glazing helps to reduce this loss considerably. As well as increasing the energy efficiency of your property, they also act as a form of soundproofing and add another layer of security to your property. They're a great long-term investment that will not only increase the comfort of your living but also add value to your home.

How much does it cost to install double glazed windows?

The cost of hiring a professional to install double glazed windows can be as little as $60 or as much as $90 an hour, depending on the complexity of the job. However, this isn't inclusive of the windows, frames or any other essential materials.

So, the question we need to be asking ourselves is 'how much do double glazed windows cost?' Double glazed windows are normally priced by the square meter, with the average price sitting somewhere between $180 and $220 (per square meter) for just the glass. As well as this, you would need to factor in the cost of the frame, which varies considerably depending on the material you choose.

When we consider the full cost of the materials, plus the labour to install the windows, you'll be looking at between $800 and $1,350 per square meter.

Remember, some key factors can change the double glazed window price considerably:

  • Type of glazing and window
  • Material of the window frame
  • Accessibility of the window

If you're looking to cut costs, consider retrofit glazing or secondary glazing for your windows instead.

How can I finance the costs of installing double glazed windows?

The costs of installing double glazing in your home can quickly add up. If you need a helping hand with your finances, here are a few places to look.

  • Credit card. Depending on your credit card limit, and the size of your installation, you may be able to pay for some of the materials using a credit card.
  • Personal loan. Personal loans are usually granted to those with good credit scores and can be used to fund renovations like double glazed window installation.
  • Redraw facilities. If you've contributed extra payments towards your mortgage, your lender might allow you to withdraw the money to spend on renovations.
  • Home equity loan. Some lenders will allow you to take out a line of credit against your home equity.

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The step by step process for installing double glazed windows

If you're considering the DIY route with window installation, or you're just interested in knowing how the process works, here are the basic steps you'll need to take to fit double glazed windows.

  1. Clean up the window frame using a chisel and brush.
  2. Remove any leftover sealant from the window unit.
  3. Check that the window fits the frame by resting it on the sill.
  4. Set the frame in the right place, add sealing tape on all four sides.
  5. Install setting blocks where necessary.
  6. Insert the window into the frame and seal with silicone.
  7. Screw the window and frame securely into place.

How long does it take to install double glazed windows?

For most residential projects, double glazed windows can be installed in less than a day. For larger or more complex jobs that require scaffolding structures, you may need to allow up to a week for the installation process to be complete.

How to choose an installer

Before you choose an installer for the job, it's worth taking the time to consider exactly what type of double glazing you want for your home. Once you've figured out the type of glazing and the frames that you want, you can set about collecting itemised quotes from local companies.

Quotes will allow you to compare different companies and the services they provide. Don't forget to check out testimonials and reviews from previous customers to make sure you hire a company that you can trust.

How to find professionals to install double glazed windows

Most professional glaziers will be able to install your double glazed windows. If you've chosen timber frames for your windows, you'll need to search for someone with a carpentry background and licenses. As well as using the powers of Google search, you can also post your jobs on websites like Airtasker to receive quotes from local companies in your area.

What questions should I ask a window installer?

Sometimes, it's hard to know who to hire to do the best job. That's why it's essential to ask tradespeople several questions before settling on one.

  • Do you have public liability insurance?
  • Can you provide a written and itemised quote for the job?
  • Do you have the appropriate licensing?
  • Can you show me a portfolio of your work?
  • What type of frames do you have experience working with?

How to negotiate with a window installer

Knowledge is key when it comes to haggling. Entering into negotiations with a good idea of what you should be charged for the job will give you more bargaining power. To do this, collect and compare as many quotes as possible from different companies. Don't forget to be respectful in your negotiations, as some tradesmen will simply walk away from a job if they feel they are being unfairly undervalued.

Expert tips about double glazed windows installation

By Chris Stead, Finder's expert DIY and home renovations writer
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Are double glazed windows worth the investment?

Absolutely. One of the key benefits of double-glazed windows is sound insulation. Double glazing does an effective job of blocking out sound, depending on what window openings you go for and how well they seal. You can still hear what's going on outside, but it's not enough to wake you.

If you're not in a noisy area, you may be wondering why that would be a selling point. But there are two additional reasons to consider; firstly, will it always be quiet where you live? What if the neighbours renovate? Or the council decides to rezone nearby land or build some infrastructure? What about the noise in your house? Like your booming home theatre? Maybe you want to keep the noise inside from getting out as much as the other way.

The second reason is because of the second bigger benefit; temperature insulation.

There are very few places in Australia that don't suffer from extremes in temperature, be it predominantly cold or hot. I'll touch on the types of double glazing in a second, but the theory of having two panels of glass separated by a gas (usually argon) chamber is to prevent the transfer of something outside from getting inside, or vice versa.

With double glazing, hot or cold hair needs to hit the first panel, transfer through, make it across the gas, and then transfer again. All while the reverse temperature is trying to do the same thing. For example, the hot summer air is trying to get in while your air-conditioned house air is trying to get out.

I've found double-glazing to work incredibly well. Every window and glass door in our home is double-glazed and the temperature in the house does a great job of self-regulating. There is plenty more that goes into that – I have good insulation crammed in every wall and in the roof, plus blinds to block out direct sunlight – but it requires a sustained day of extreme temperatures before I need to resort to the air-conditioner downstairs.

Upstairs, where the sun directly hits the roof and to which hot air rises, I do need to cool the rooms before sleep on hot nights, but then the double-glazed windows do a good job of keeping that cool air inside the home. So, I usually only run the air-con for 30 minutes before bed and then maybe again in the middle of the night for 30 minutes on belting hot or frigid evenings.

Can you install double glazing yourself or is it better to call in a professional?

Most window companies will install their windows for you either directly or through a preferred trade at an additional cost. I didn't go this route; but I wish I had. We had the windows delivered and then installed them ourselves with the help of the carpenters that were working on the framing and external cladding. While we did get the job done, it cost me more in their labour than it would have to get the professionals to do it simply because each manufacturer has their own quirks.

And then the job wasn't as good because the local chippies weren't familiar with the product.

Plus, these windows are bloody heavy. Our biggest windows were approximately 2 x 1.4m and it required four guys to lift it up onto the sill. Then it must be fixed into place while you're holding it. Not only is that a lot of labour cost, but there's a lot that can go wrong when you are moving objects with that much weight. Scratches, dents and worse are possible, which is why it's good if it's all on the head of the professional installer.

Of course, these issues may not be a concern if you're just putting in one or two small windows, but it's also important to remember that windows and doors – especially sliding doors held in a track both top and bottom – will rarely just fit perfectly into place. There's a fair bit of work to do getting them level, packing them into the cavity and securing them. As such, you'll likely need some in-the-moment carpentry done, which you'll either need a chippy on hand for or have the ability to do yourself.

What type of window glazing would you recommend?

In general, your options are:

  • Double glazing separated by a vacuum
  • Double glazing separated by a gas
  • Low-e double glazing separated by a vacuum
  • Low-e double glazing separated by a gas

As you descend that list, the insulation improves, but so does the cost. Then each again is impacted by the thickness of the glass panels and the gap between them. The vast majority of Australians will be used to days or even weeks of very hot weather. Some of us experience cold weather, too. But most of us don't live in freezing conditions (such as Scandinavians) or relentless heat (like Indonesia) all the time.

My point is that you don't have to go over the top. You can likely get away with glass 4 to 6mm thick, and then a gap between the panels around 6 to 10mm, depending on where you live and how much direct sun the window gets.

As for low-e, this refers to emissivity. Effectively this option has a film coated onto the glass to help further reduce the transfer of energy. There are other options in this regard, too. Tinted and reflective glass, or colour toned, for example. There's even laminated glass which doesn't shatter and does a good job with sound.

What did I do? I went for a 6-8-6 double glazed window separated by gas. (As in two 6mm panels separated by 8mm of Argon gas).

What type of double-glazing window frame would you recommend?

There are three main frames to think about; aluminium, timber and uPVC. Let me steer you away from timber straight away. It looks great and has solid insulation capacity, but the upkeep – painting or staining - is never-ending. They're harder to clean. Plus, they're harder to seal as they expand and contract in the heat, meaning they do a poor job on sound.

Aluminium is cheaper, gives you a wide choice of colours, a decent sound seal and it's easy to clean. They can find a scratch that's for sure, but their main downside is that the metal is a temperature conductor. This can mean all the hard work your glass is doing can be undermined by its frame. Aluminium frames are also relatively heavy.

The third option, which has become more affordable since I built my house, is uPVC (Unplasticised Polyvinyl Chloride). Yes, it's a plastic, but made rigid and sturdy like metal. It's got plenty going for it. It's lightweight, fire tolerant, doesn't colour fade (although there are less colour options to begin with) and is strong enough that it doesn't need to be as thick as aluminium or timber, which means more glass to look out of.

What I like most about uPVC as an option, however, is that it seals better than the other materials, providing better sound and heat insulation. Well, if you can afford it.

In recent years, we've also started to see fibreglass window frames enter the Australian market. It's an awesome product or framing due to its strength, its ability to tolerate temperature extremes without moving and its incredible insulation. It has been known to leak, however, and it is still very expensive.

I went for aluminium on my home, although I had it thermally broken. This add-on puts a rubber buffer in the frame, effectively splitting it into two halves; the rubber slows down the transfer of temperature through the frame. As I was buying so much glass to fit out a two-storey home, I decided to put my money into the double-glazing itself, and pare back on the framing. I'm happy with the results, though I would have loved to have got the tighter seal of uPVC had my budget stretched that far.

How should double glazed windows open for best results?

Taking a broad view, you'll be looking at three types of window opening systems. The classic slider, the casement/tilt and the hung. Casements offer a much better seal, which is good for temperature but mostly ideal for sound. Sliders and hung windows are easier to flyscreen, but seal poorly in comparison.

We went with sliders in most rooms and it was a mistake as sound was a big concern for us given we live opposite a park. I should have gone with casement windows and spent more on a bespoke, imaginative fly screen solution (for example one that isn't fixed but can be slid to the side for window access).

If sound isn't an issue for you, however, then the world is your oyster.

Is retrofitting double glazing to your existing window worth it?

If you're not building a new structure, but are instead looking to improve your existing residence, then retrofitting is worth considering. This allows you to keep the existing frame and cavity, and either add in a new double-glazed glass in full, or to just add a second glass panel to create a double-glazed effect from your existing single pane window.

The reason why you'd want to retrofit rather than put in a whole new window is because the removal of your existing window would be very invasive and expensive. This is because the window frame is usually embedded in both the internal and external structures. To remove it you'd need to destroy all the architraves, any windowsill, potentially some gyprock and then, outside, some cladding, bricks or render. It's near impossible to remove these elements cleanly as they were likely glued into place and/or full of screws and nails that have failed over the years and won't come out. Or, in an old home, it could be asbestos!

Then once you put the new window back in, all those elements you just destroyed need to be re-built, painted and finished. It's a huge cost.

So, unless you simply can't live with the existing frame, retrofitting is a much smarter option. Plus, it gives you the flexibility of focusing first on windows that get direct sun or sound; you don't have to get every window done at once if budgets don't allow.

About Chris Stead

Finder's expert DIY and home renovation writer, Chris Stead, spent two years as an owner-builder. He was involved day-to-day from the groundwork up in constructing a two-story family home with a pool and separate granny flat. Working alongside every trade on the journey, tools in hand, he went through all the successes, failures, stress and financial decision making required to renovate in Australia.

Pros and cons of installing double glazed windows

Pros

  • Increased energy efficiency
  • Save money on utility bills
  • Aids noise reduction in the home
  • Adds another layer of security
  • Reduces the chance of mould in the home

Cons

  • Can be very expensive initially
  • Susceptible to damage in the air gap
  • Modern aesthetics don't suit all homes
  • Traps heat during summer months

Bottom line

There's no denying that double-glazed windows are an expensive investment. However, with benefits like energy savings and added value to your home, you're likely to reap back the costs in the long run.

Frequently asked questions about double glazed windows

How long do double glazed windows last?

Double glazed windows can last as long as 20 years, however, some units experience problems within ten years of installation. This is usually down to poor installation. Most reputable companies will provide a ten-year warranty for your double glazed windows.

How much does it cost to replace misted double glazing?

Replacing your double glazed windows can be costly. If you need the whole glass panel replacing, you'll need to factor in the cost of the glass plus labour. Expect to pay anywhere between $500 and $1000. If the repair is due to incorrect installation, check to see if the company provides a warranty before forking out on repairs.

How can I tell if my double glazing needs replacing?

There are a number of tell-tale signs that suggest your double glazing needs replacing:

  • Draughts around the window
  • Cracks in the windowpane
  • Increased energy bills
  • Condensation between the glass panes
  • Difficulty opening and closing windows
  • Leaking during wet weather

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