Double Glazing


What is double glazing?

All properties lose heat through their windows. Installing energy efficient double-glazing is an effective way of reducing your energy bills and keeping your home warmer and quieter.

Double-glazed windows use two sheets of glass with a gap between them which creates an insulating barrier, whilst triple-glazed windows have three sheets of glass. Both options can deliver a high level of energy efficiency; it is not the case that you have to use triple-glazing to gain the most energy efficient window.

The space between the glass panes can be filled with either a vacuum (quite rare nowadays because they require excellent sealing, otherwise the vacuum diminishes so the efficiency decreases), or a heavy inert gas such as Argon, Krypton or Xenon. Both these methods are trying to create a more effective insulating barrier, known scientifically as increasing the R-value (which is the measure of thermal resistance).

Energy efficient double-glazed windows are available in a variety of frame materials (including uPVC and more traditional wood) and styles. These windows vary in their energy efficiency, depending on how well they stop heat from passing out through the window, how much sunlight travels through the glass and the amount of air that can leak in or out around the window.

Some double-glazing window and door manufacturers helpfully use a window energy rating scheme to show the energy efficiency of their product. This is similar to the one you may have seen on appliances such as your fridge, or washing machine. A-rated windows are the most efficient. To check a window’s energy efficiency before you buy, look at its energy label.

Questions to ask yourself before investing in double glazing:

1. How energy efficient are the windows?

When choosing replacement double-glazed windows, you can check their energy efficiency by looking at the Energy Saving Trust Recommended logo and British Fenestration Rating Council (BFRC) energy label. The higher the energy rating, the more energy efficient it is. The Energy Saving Trust endorses any windows rated B or above. Unfortunately, at the moment there is no obligation for window manufacturers to label their products; however by opting for a highly-rated window you know you will be buying the most efficient.

For a list of all types of double-glazed/triple-glazed windows and their frame material and energy rating, visit the BFRC website.

2. How many layers of glass is best?

Double glazing has two layers of glass with a gap of around 16mm between them. There’s also the option of triple glazing, which has three layers of glass. Both A-rated double and tripled-glazed windows are available.

3. What type of glass is best?

The most energy efficient glass for double-glazing is low emissivity (Low-E) glass. This often has an unnoticeable coating of metal oxide, normally on one of the internal panes – next to the gap. It lets sunlight and heat in but cuts the amount of heat that can get out again.

4. What is between the panes?

Very efficient windows might use gases like argon, xenon or krypton in the gap, or a vacuum between the two sheets of glass.

5. What keeps the panes apart?

All double-glazed windows have pane spacers set around the inside edges to keep the two panes of glass apart. For a more efficient window, look for pane spacers containing little or no metal – often known as ‘warm edge’ spacers.

The BFRC window energy rating scheme checks all the components to ensure the final window achieves the energy efficient standard claimed. This means that you just need to look for the A-G ratings and remember A is best! Alternatively, just look for the Energy Saving Trust Recommended logo which will only be found on glazing that is B rated or above.

6. Which frame suits your home?

The frame you choose will depend on your home and your personal taste. For all frame materials there are windows available in each energy rating.

7. Do you need ventilation?

Because replacement double-glazed windows will be more airtight than the original single-glazed frames, condensation can build up in your house due to the reduced ventilation.

If there is not a sufficient level of background ventilation in the room, some replacement windows will have trickle vents incorporated into the frame that let in a small amount of controlled ventilation.

Condensation can sometimes occur on the outside of new low-e glazing. This is because low-e glass reflects heat back into the home and as a result the outside pane remains cool and condensation can build up in cold weather – you don’t need to worry about it.

Benefits of installing double glazing

Lower energy bills: replacing all single-glazed windows with energy efficient double-glazing could save you around £135 per year on your energy bills.

A smaller carbon footprint: by using less fuel, you’ll generate less of the carbon dioxide (CO2) that leads to global warming.

A more comfortable home: energy efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.

Peace and quiet: as well as keeping the heat in, energy efficient windows insulate your home against unwanted outside noise.

Reduced condensation: energy efficient glazing reduces condensation build-up on the inside of windows.

The costs and savings of double glazing will be different for each home and each window, depending on the size, material and installer. Savings will also vary depending on how much you currently pay for your heating fuel; these savings are based on a gas-heated home.

Installing double glazing

When you plan an installation, you need to know about building regulations and what to do if double-glazing doesn’t suit your property, as well as how to maintain your windows. When you think about replacement glazing, you need to make sure your windows are installed correctly and comply with all the relevant regulations.

Building regulations

Under building regulations in England and Wales new and replacement windows must meet certain energy efficiency requirements:

New and replacement windows in existing homes in England and Wales must be at least WER band C or U-value 1.6 In Scotland must be at least WER band C or U value 1.6 In Northern Ireland must be at least WER band E or U value 2.0 or centre pane U value 1.2.

However, if you live in a conservation area, have an ‘article four’ direction on your property or have a listed building, additional regulations are likely to apply. Before you do any work, make sure you check with your local planning office. An ‘Article 4’ direction removes the right of permitted development, meaning that you will have to apply for planning permission before replacing any windows. This is often applied in conservation areas.

How to comply with regulations

To make sure regulations are complied with, there are certain rules about the way you can install windows:

Find registered installers

FENSA guarantees that its installers and frames comply with building regulations. To find a FENSA registered installer, visit the FENSA website.

Certass is another scheme that registers and approves installers. To find a Certass registered installer visit the Certass website.

Ask your installer when you will get a certificate after installation is completed, which demonstrates the installation has been completed in compliance with building regulations.

Other options for improving the energy efficiency of your windows

If you can’t install double-glazing (e.g. if you live in a conservation area or in a listed building) you have other options:

Heavy curtains

Curtains lined with a layer of heavy material can reduce heat loss from a room through the window at night and cut draughts. They will save some energy, but should only be used as a short term measure.

This could be something to think about when re-decorating!

Secondary glazing

Secondary glazing works by fitting a secondary pane of glass and frame, inside the existing window reveal. This is likely to be less effective than replacement windows, as the units tend to be not as well sealed, however it is considerably cheaper than double-glazing. Low emissivity glass is available for secondary-glazing, which will improve the performance.




The Energy Saving Trust endorses any windows rated B or above.

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      Home Energy Efficiency Misconceptions

      April 9, 2013

    Continuing on from the blog last week, discussing some of the early feedback on the Green Deal, I want to look at some of the misconceptions people can have when considering energy efficiency improvements. These can stem from a variety of sources, for instance: out of date knowledge on certain technologies, biased opinion from contractors selling their products, and in some cases just uncorrected assumptions from the home owner. It is of course important for a Green Deal advisor to try and clear up these misconceptions, and allow the home owner an unbiased and straight-forward explanation of energy efficiency measures and here are some common examples:

    Walls, Roofs, Windows and Doors Energy Misconceptions

     Boilers and Hot Water Tanks Energy Misconceptions

    Habits and Lifestyles

    A final Point

    Another point that has been stressed in previous blogs is that halogen bulbs are not low energy! They are in fact very inefficient and switching to LED bulbs will save a lot of money, relative to the cost of the bulbs, also since the last significantly longer (10-20 years longer), you won’t have to get your ladder out every 6 months to replace a blown bulb!


      Ed’s Blog: Home Improvements – Small Things Do Add Up!

      February 4, 2013

    With all the windy weather recently, I’ve noticed how my house is a bit draughty – it actually sings to me as the air rushes in and out of the small gaps in the windows and doors! To stop this singing, I seriously looked into draught exclusion to try and keep as much of that precious warm air from escaping. I was quite surprised at how much energy I could save (and money!), therefore this blog details not only how I found ways to draught-proof a house, but also suggest some other cheap methods to help your house become more energy efficient.

    While it’s good to have effective ventilation throughout the house to ensure good air flow through the house to help reduce any condensation or damp, (I’m not looking for a completely airtight building), but draughts are actually pretty costly from an energy point-of-view.

    Here is how I tackled my doors

    I have two entrances to my house, a front and a back door, both of which have fairly old doors on them. As the house is a little bit exposed to the elements (it sits on a slight hill so we get the full force of the wind and rain), I think the old wooden doors have warped a little bit and don’t sit flush with the frame. I noticed the previous owners had put in some foam strips to try and stop the air flowing through, however it didn’t appear that it helped that much. So, this is what I decided to do to improve the situation:

    All these measures cost under £25 per door and a quick look online shows that I would save at least that amount over a year. With the payback of 12 months, it is a no-brainer!

    Windows in good shape

    The windows are actually in pretty good shape (the FENSA certificates when I bought the house said they were installed between 2006 and 2007) so no work is needed there. But you can do similar things with the self-adhesive foam strips on the windows or even more permanent metal strips (though these tend to be more expensive). You can even put silicon sealant on windows that don’t open to get a really snug fit.

    Loft – quick and easy seal

    I also noticed when I was up in the loft (looking at the water system – will have a separate blog on this at some stage), I noticed that there is a bit of air rushing in and out of the hatch, so I sealed that with some foam strips on all four sides, much like you can do with a normal door (cost less than a fiver). Quick and easy and probably making a marginal benefit that will help in the long-run.

    Shutting out that chimney noise

    When the air Source heat pump engineer came round a couple of weeks ago to look at the possibility of installing a pump, he commented on the fact that I have two disused chimneys in the house. This is a problem as they also appear to be letting a lot of the heat out. One option is to install a cap on the chimney, but I’m quite keen to get the fireplaces up and running over time, so I’ve invested in a genius device called a “chimsoc”, which is a plastic, inflatable, reusable balloon.

    Chimney Balloons

    Basically, you place it halfway up the chimney, inflate it and it sits there keeping most of the warm air from escaping! It’s got a slight gap at one side to allow for a little bit of airflow and a handy dangling device which can be seen in the fireplace and will stop me inadvertently lighting a fire while it still up there! They are also good for reducing any noise, especially if like me you live in a busy area – near a main road or railway line.

    A bit of expanding foam on external pipework

    My house has quite a few pipes running in and out it. In pipes for gas and water from the well, and out for waste water (sinks, showers, toilets etc). I invested in a can of expanding foam (£8 from B&Q) and filled the gaps around these pipes. It’s amazing stuff (be careful and use gloves though as it’s quite sticky!) and has reduced the draughts considerably. You can spray it in and then saw off / sand down any excess.

    All in all then, I have spent under £90 on a number of measure I have installed above (you might need to spend a little more if your windows need a bit of draught proofing), but improved my house extensively. I can already notice the difference in the reduced draughts and hopefully soon I’ll start noticing the savings in my heating bills.

    Hope to this was useful.

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