Energy efficient windows and doors

There are different types of window glazing. Single glazing is where there’s a single pane of glass in the window. These aren’t as energy efficient as the other types that we recommend here.

Double glazed windows have two panes of glass to make up a window. A spacer bar separates the two panes. The gap in the middle is filled with air or an inert gas like argon, which is even more insulating than air. This creates a barrier that reduces heat loss and improves the insulation of the window.

Double glazing helps keep warm air inside your home during the winter, which helps reduce energy bills. It also helps keep hot air outside your home during warmer weather.

Triple glazing is where three panes of glass make up a window.

Like double glazing, triple glazed windows contain air or an inert gas between each pane. This can give the windows better insulation compared to double glazing, eliminating draughts and noise, reducing heat loss even more. This can help make your home feel cosy while reducing your energy bills.

Secondary glazing is where you fit pane of glass or transparent material on the inside of an existing window.

This can be cheaper than installing new windows, but it all depends what type of secondary glazing you install. Examples include:

• Secondary glazing film: This thin transparent film of plastic is a cheaper option that you can usually fit yourself. However, it doesn’t last long and can be hard to make aesthetically pleasing. It offers the least thermal benefits of the options available.
• Magnetic secondary glazing: This uses magnetic strips or clip-fit mounting systems to attach a supplementary pane of glass or plastic to the inside of your window. It can help reduce heat loss and can be easily removed or replaced.
• Permanent secondary glazing: This involves custom-built frames and glazing and can be wooden or uPVC. It’s a more expensive option, but it can be more energy efficient than replacing the windows. It’s also a suitable option for homes with restrictions like listed building regulations.

Energy efficient windows come in a range of frame materials and styles.

How energy efficient a window is depends on a few things, which makes it difficult to choose them just by looking how they’re made. However, there’s a rating scheme to help you find the most efficient option in your budget.

Window and door manufacturers show the energy efficiency of their products using an energy-rating scale from A++ to E. This rating scheme is run by the British Fenestration Rating Council (BFCR).

The entire window (the frame and the glass) is assessed to consider:

• heat loss
• draughts
• solar gain (this is where the sun’s warmth is transmitted through the window)

This gives a rating that shows the overall impact of fitting that particular window in your home.

Windows with an energy rating will have the ‘u-value’ of the window displayed on the energy efficiency label. You might also see u-values quoted for windows without a label.

A u-value is a measure of how easily heat passes through a material, but it’s not a complete measure of how efficient a window is. The overall energy efficiency rating provides a better indication of the window’s energy saving potential.

The cost of energy efficient windows varies depending on the materials and style you choose. It also depends on whether you choose double glazing or triple glazing.

PVC windows tend to be cheaper, while hardwood frames are the most expensive.

A set of A-rated windows for a semi-detached house will typically cost around £12,000.

Installing A-rated double glazing in an entirely single-glazed semi-detached home can save £140 a year in GB and £140 in NI.

This will also reduce CO₂ emissions by 380kg a year in GB and 550kg in NI.

You should consider any regulations that may affect what windows you can install if you live in a conservation area or listed building.

In areas of special architectural or historic interest, any work you carry out on your home must preserve or enhance the character of the area.

This doesn’t necessarily mean you can’t replace your windows. However, it might mean you’ll need to get windows that complement the character of the building and area.

Some companies can provide double glazing in these types of properties, where double glazing can be made to look like the building’s original windows. But for any changes you want to make, you’ll need to contact your local council’s conservation officer for guidance.

You’ll need permission if you want to make changes to windows in a listed building.

Old windows in historic properties can be protected, not just for their appearance, but also for the materials and methods used to make them.

Secondary glazing can be a non-intrusive way of insulating historic windows from the inside. Non-intrusive window insulation options for historic homes include:

• heavy lined curtains
• shutters
• secondary glazing
• sealed blinds

Check with your local council to see what options are available to you.

Historic Environment Scotland and Historic England also have advice about how to make a historic home more energy efficient.

Sash windows are common design features of period properties. They consist of two vertically sliding frames and are typically made of a single pane of glass. But they often don’t have an airtight seal, which gives them poor insulating properties making them prone to heat loss.

Want to upgrade your sash windows? There are energy efficient options that remain in-keeping with original design and materials so you don’t compromise the original look:

• Replacing the glass panes for double or triple glazing without replacing original frames. There are slim-profile options available.
• Draught proofing using discrete seals, weather strips or caulking around existing frames that can’t be seen.
• Fitting new units into existing frames can be done in some cases.
• Repairing old frames, checking for rotting wood and cracks can help.
• Secondary glazing will reduce energy loss and reversible options don’t usually doesn’t need listed building consent.

Modern windows will usually be more airtight than old windows and will have seals around the openings. Replacement windows will usually have trickle ventilators to provide ventilation into your rooms. These are sometimes called ‘background ventilators’.  

You should keep your trickle ventilators open. For more information, read our guide on ventilation.  

If you notice condensation in between the panes, this likely means that the double glazing is letting air in. This reduces the windows’ effectiveness, so it’s possible to replace the double glazing panes rather than the whole window unit.

Condensation on the outside of your windows isn’t a problem. In fact, it’s a sign that your windows are very efficient. The condensation will clear quickly and won’t lead to any damp problems.

If you start to see condensation building up on the inside window or wall, this could be a sign of a potential damp problem.

Find out how to fix damp and condensation in your home.

Modern external doors usually have effective draught-proofing around the outer edge of the door and the frame. Letterboxes will also have seals around them. 

Composite and uPVC doors often have insulated cores. Aluminium doors may feature ‘thermal breaks’, where there’s insulating material between the layers of the door. This helps keep the heat in your home when it’s cold and the heat out when it’s warm. 

If you have older doors that are draughty they can be draught-proofed and insulated to reduced heat loss. For more information, read our advice on draught proofing. 

Newer glazed doors should have double or triple glazing. 

We recommend you use a professional installer for installing new windows and doors.  

Before replacing windows, check with your local planning office if:

• You live in a conservation area.
• You have an Article 4 Direction (A4D) on your property that removes the right of permitted development in certain areas or properties.
• You live in a listed building.

This is to make sure you comply with any requirements that apply to your home.

You should choose an installer that’s registered to a competent person scheme. This is an easy way to make sure your windows are fitted to building regulations.

If you use an installer who isn’t registered with a scheme, you’ll need to apply for building control approval before installing the window. The UK Government planning portal has information about how to apply for building control approval.

In Scotland, each local authority has a building standards office. Check with them first to see whether you need a building warrant for your new windows.

We recommend getting quotes from at least three installers to help you get the best deal. You can find local, certified installers using TrustMark, which is a government-endorsed quality scheme for tradespeople.

For double glazing, the Glass and Glazing Federation (GGF) is a membership organisation whose members sign up to a consumer code. This means that you should get excellent customer service. If one of their members fits your windows but you’re unhappy with the work, you can use GGF’s free reconciliation service.

As secondary glazing is more specialised than double glazing, there isn’t currently a central body that certifies these installations.

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