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Double glazing: your questions answered

In this weeks blog we explain some advantages of double glazing, how much you could save on your energy bills and hopefully answer your most common questions.

For many people, installing double glazing will mean smaller energy bills and a warmer house. In fact around 51% of people who have had double glazing say that they bought it to make their home warmer, and 44% to reduce their energy bills.

But it can be expensive, so you want to make the right decision for your house. Here, we answer your questions such as.

  • Is double glazing efficient?
  • Are there benefits to triple glazed windows?
  • What is secondary glazing?
  • Will getting double glazing reduce my energy bills?
  • What are energy ratings for double glazing?
  • When does double glazing need replacing?
  • How much do double glazing units cost?
  • Can you replace double glazing yourself?
  • Can double glazing reduce noise and soundproof?
  • Does double glazing cause damp or condensation?

Is double glazing efficient?

Double-glazed windows consist of two panes of glass separated by a layer of air or gas. They have many benefits over single glazing where there’s just one pane of glass and no air layer or gas:

  • They keep warm air in, meaning your home is better insulated. This results in dramatically fewer draughts and cheaper heating bills.
  • They keep noise out. You will hear less noise from outside.
  • They reduce the amount of condensation on the inside of your windows.
  • They heighten security – the glass is more difficult to break than single glazing.
  • The most efficient glazing has gas between the panes such as argon, and use low-emissivity glass (Low-E), which has a reflective coating to help bounce sunlight back into a room.

Double glazed windows

Are there benefits to triple glazed windows?

Triple glazed windows

Triple glazed windows essentially have a third pane of glass, so they should theoretically make your house warmer and more sound-proof than double glazed windows. Some companies will also use different types of gas between the panes to prevent heat loss and Low-E glass to reflect sunlight inside the room. As you would expect, triple glazing can be more expensive than double glazing. If you’re really keen on getting it but the cost is prohibitive to do your entire house with them, you could consider having triple glazing on the rooms that get coldest or suffer worst from external noise.

What is secondary glazing?

Secondary glazing involves fitting a second layer of glass inside your current windows. It is not as good as full double glazing, but they could still save you some money on your heating bills.

It could also be the alternative for properties that can’t install double glazing, for example if your property is a listed building.

Will getting double glazing reduce my energy bills?

67% of homeowners said that their home is definitely warmer since getting their new windows. However, only 35% said that they thought it had reduced their energy bills.  

If all of the single-glazed windows were replaced in a detached house with A++ double glazed windows, the Energy Saving Trust says that you would save between £110 and £115 per year. For a mid-terraced house, where it is attached on both sides and so would naturally use and lose less heat, it would be around £60.

House glazed windows heat map

What are energy ratings for double glazing?

The energy-rating system for double glazing has a similar pattern to appliance energy labels, with windows being rated between A++ (best) and E (worst). Building regulations require all new windows to be at least C-rated.

When looking at energy savings, the Energy Saving Trust estimates that for a detached house with all double glazed windows, the savings for a C-rated window would be about £95 this is between £20 and £15 less than A++ ones. For a mid-terraced house, it would be £50 – just £10 lower.


U-Value is a measure of how easily heat can pass through something. The lower the amount of heat the material lets escape, the higher the U-Value will be.

Double glazing energy ratings

Some windows might have a high energy rating, but low U-Value because the energy rating looks at all aspects of the window such as types of glass or gas not just how well the materials insulate, so they might be better overall.

When does double glazing need replacing?

The majority of people (69%) said that the reason for getting double glazing was to replace existing ones. If you’re unsure whether your windows need replacing, these signs should help you choose:

They are:

  • Draughty.
  • Are leaking, letting water in.
  • Allowing excessive amounts of noise in.
  • Yellowing or timber is cracking.
  • Visibly damaged, particularly to the seals.
  • Difficult to open, close and lock, or are sticking.
  • Often covered in condensation, particularly between the panes of glass.

How much do double glazing units cost?

Prices can range from £515 for one 60 x 90 cm uPVC casement window to more than £3,000 for a large 180 x 150 cm double hung sash window. There are a lot of things that can affect the price of your double glazing, including:

  • the type of windows you choose;
  • the material (uPVC is usually the cheapest);
  • and how many you need.

Can you replace double glazing yourself?

New double glazing needs to meet certain building regulations and they need to be approved by Building Control. So because of this, it’s not advisable to install your windows yourself.

Can double glazing reduce noise?

While only 20% of the people we surveyed got double glazing because they wanted to block out noise, nearly half of them believe that getting it has actually decreased exterior noise.

As double glazing consists of two panes of glass instead of one, it’s likely to cut out more sound that single-glazing.

Does double glazing cause damp or condensation?

Damp old window

Any condensation on your windows or doors can be a sign that it needs replaced. However, in some instances, double glazing can cause damp. This is because all homes need to have ventilation.  This can be a problem in winter when it’s cold outside and warm in your house which results in moisture collecting on cold surfaces like glass.

To help avoid any problems, when you are getting new double glazing, make sure you think about the ventilation in your property. A way to allow a small amount of air in and moisture out is to have trickle vents in the frames of your double glazed windows. You could also think about tilt and turn windows which allow you to tilt the window or door to let a small amount of air in while still keeping it locked.

Visit our windows page for more information.