Will secondary glazing reduce my heating bills?

If you’re thinking about making energy-saving improvements, secondary glazing is one project that can make a real difference to your household bills.

According to the Centre for Sustainable Energy, approximately 10% of total heat loss from a typical home is through the windows, and a further 15% is due to draughts.

Fitting secondary glazing can make a significant difference, and providing that it’s installed correctly, energy bills can fall substantially.

Let’s investigate the pros and cons of secondary glazing.

What is secondary glazing?

It’s a way of adding a layer of glazing to windows that are single-glazed. An extra layer of glass is installed on the inside of an existing window pane to help improve thermal efficiency and reduce heat escaping by effective draught proofing. As well as glass, secondary glazed options include clear acrylic which is lightweight and shatterproof, and clear polycarbonate which is stronger and ideal where security is an issue.

Advantages:

  • Secondary glazing is thermally efficient: if properly installed and sealed, a secondary glazed window will reduce the amount of heat lost and keep cold air out.
  • As secondary glazing doesn’t alter a house’s appearance, it doesn’t usually need planning permission.
  • It is often suitable for houses in conservation areas or in listed buildings where double-glazing units are not permitted, and there are specialist suppliers.
  • Some types of secondary glazing you can fit yourself; others need specialist fitting.
  • It’s a cheaper option than double glazing, which traps air or gas between the panels and involves total window replacement: secondary glazing attempts to replicate this insulation gap to reduce heat escaping.
  • In some cases, homeowners who installed secondary glazing have seen energy bills fall by around 40% – according to Grand Designs, you can approximately double a home’s energy efficiency.
  • Secondary double glazing is easily reversible.
  • It’s also durable – it doesn’t corrode and can have a long life expectancy.
  • Secondary glazing can be included in a retrofit scheme to improve a home’s Energy Performance Certificate rating. It can be a sustainable retrofit solution when replacing existing windows is not allowed; by not removing the windows, existing embodied carbon is undisturbed.
  • While 75% of homes have double glazing windows, some early sealed units dating back to the 1980s are less efficient than modern versions. Secondary glazing can help upgrade these poorly performing windows.
  • Secondary glazing is thought by many to be more efficient than double glazing as the latter can fail and have higher lifecycle and energy costs.
  • It can reduce noise from the roadside by using acoustic glass which aids sound insulation. Toughened glass can also be used for security reasons.
  • Secondary glazing is a one-off investment that doesn’t cause too much disruption.
  • If properly installed, an unobtrusive secondary glazing system can be almost invisible from the exterior of the house. It can also be bespoke to specific windows.
  • For renters who are not allowed to make structural alterations to windows, secondary glazing can be an affordable solution.

Disadvantages:

  • The thermal efficiency of secondary glazing depends on how well it’s fitted, and the condition of the original windows and seals.
  • Plastic panes such as acrylic or polycarbon will deteriorate as they are exposed to light, becoming less clear.
  • While a good quality system can match existing windows well, other secondary glazing units may not look very pleasing aesthetically.
  • Some panels can be difficult to clean and maintain, although you can get easy access removable panels to take out and clean.
Triple glazed casement windows can offer improved thermal insulation.

How does secondary glazing compare to double and triple glazing?

It’s important to remember that the effectiveness of secondary double glazing depends on the quality of the existing primary window that it is fitted to. Double and triple glazing units are sealed, unlike secondary glazing which has a higher `u’ value as a result (a measurement of the rate of heat loss through a window), making it less effective. The fact that secondary glazing panels are further apart than those in sealed units also affects efficiency, and fitting it onto an existing frame creates more potential for gaps in the seals. However, the use of low emissivity glass can help performance and reduce heat loss.

Secondary glazing options

If you decide to fit secondary glazing, your options range from inexpensive DIY systems that you can buy in a hardware store, to those needing professional installation. While professionally fitted secondary glazing offers custom-built frames and glazing, often with low-E glass to retain heat, it costs more but can be better than installing replacement windows according to the Energy Saving Trust.

Temporary secondary glazing solutions

Here, a sheet of rigid and transparent material, such as clear acrylic plastic or clear polystyrene, is fitted to the existing window frame. It can be removed in summer and attachment options include magnetic strips or Velcro-like material, or panels can be clipped into place with uPVC edging. This is the cheapest DIY option and can be both effective and removable. The price to insulate a bay window with this method is around a cost effective £15, and the kit can be bought at DIY stores.

Semi-permanent secondary glazing

This is fixed by strong adhesive or screwed into place. It can be made from glass and can slide open on tracks to allow windows to open. Clear lightweight acrylic panels can fit over glazed sash windows, though they won’t cover the gaps on the sides, top, and bottom of the frames.

Further options

There are secondary glazing systems for horizontal sliding secondary glazing, options that swing open, or wooden, aluminium, or plastic frames. Some can be permanent or removable in summer. Lift-out secondary glazing looks appealing as it has few frame lines; this option is best for windows that are not opened frequently as the whole panel needs to be lifted out to access. Hinged units will open into the room like a casement window, while a horizontal option slides to one side to allow a window to open. Vertical sliding secondary glazing is usually used with sashes.

Secondary glazing can be an option when dealing with windows in listed buildings.

Is it really worth installing secondary glazing?

The payback time for secondary glazed windows could be between 5-10 years; for double glazing, the payback time is between 20-30 years, according to Homebuilding.co.uk. Bear in mind that installing secondary glazing might not add value to your house.

How much does secondary glazing cost?

The cost varies enormously because of the wide-ranging options. As a general estimate, prices can vary from £50/m2 to £300/m2. Double glazing can cost between £200/m2 and £700/m2.

For a rough guide, it can cost from £5,000 to install secondary glazing in a semi-detached home, but a far cheaper option is to get a custom cut Perspex acrylic magnetic secondary glazing kit from a company such as Cut Plastic Sheeting which you can install yourself. The cost of seven secondary glazing acrylic kits for seven windows is £151.

According to Grand Designs, secondary glazing costs approximately 50% less to supply and install than double glazed windows.

Over to you

Have I missed any points about secondary glazing? 

Have you found that secondary glazing has significantly reduced your energy bills or lessened external noise? Perhaps you have installed it in a listed building?

If you can add any useful information, we would love to hear about it. Please comment in the box below.

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