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Secondary Double Glazing

Secondary double glazing, sometimes referred to as ‘secondary glazing’, simply means fitting panes of glass inside your existing single pane windows to achieve many of the same benefits as double glazing. The additional pane of glass has an insulating effect similar to that which double glazing provides, but at a much lower cost.

The greatest advantage of secondary glazing is its affordability. If you would like to lower your heating bills, reduce draughts and keep your home warmer in winter but don’t have the budget to install double glazing, secondary glazing may be the next best option.

Historic window

Secondary glazing is suitable for historic windows which cannot be replaced

Owners of listed properties also frequently decide to have secondary glazing installed, as it allows them to keep the property’s original heritage windows.

Affixing secondary glazing over the inside of a listed property’s existing windows is usually deemed a reversible alteration.

So if you own a property in which irreversible alterations are prohibited, secondary glazing may be your only option.



Types of secondary glazing

There are several varieties of secondary glazing. The type you choose depends on your budget, the type of windows in your home, and whether or not you’d like to open your windows.

If you would like to still be able to open your windows after installing secondary glazing, the most common options are vertically-sliding or horizontally-sliding panels.

The former are simply panes of glass that slide down into fitted tracks. The majority of vertically-sliding secondary glazing panels can be tilted back for cleaning.  The latter, horizontally-sliding panels, are panes of glass that slide horizontally across pre-fitted tracks. They, too, can be cleaned easily. Just slide the panels over each other for access to the glass.

If you don’t need to be able to open your windows, you can also consider installing removable panes of glass over your existing windows. This type of installation is often quite affordable, and the panes of glass can still be removed for cleaning. It’s often an appropriate choice for smaller windows and for windows in hallways, but not a common choice for bedroom windows.

One very important consideration is fire safety. Being unable to open any of your windows during a fire can obviously be quite dangerous and is a situation you should avoid. Although in a true emergency one could simply break both panes of glass on a secondary glazed window, windows that open are still the safer choice.

If you decide to install non-sliding secondary glazing in your home, be sure that at least one window on each floor opens wide enough for an adult to escape through. Also, since regulations vary from region to region, remember to check with your local council for any fire safety regulations that may apply to your property.


Is secondary glazing the right choice for you?

As mentioned above, homeowners on limited budgets and those subject to the restrictions of a listed building often choose secondary glazing. However, even if regular double glazed windows fit your budget and you do not own a listed property, it may still be the right choice for you.

If your current single pane windows are in good condition, secondary glazing might be a good option for your home. As long as the glass in your current windows is not warped and the frames are in good shape and fit snugly against the walls of your property, it makes little financial or environmental sense to tear the windows out and replace them with new double glazed windows.


Disadvantages of secondary glazing compared to double glazing

Secondary glazing, though it does enhance a home’s ability to retain heat in colder seasons, is simply not as effective as double glazed windows.

The techniques used to attached secondary glazing panes to a window frame mean that the two panes of glass (your old single pane window and your new secondary glazing) are often placed farther apart from each other than the double panes of glass in a regular double glazed sealed unit. This reduces the window’s ability to prevent heat conduction between the inside and outside of your home.

Rotten window frame

There is little point installing secondary glazing over rotten, badly fitting windows

The effectiveness of secondary glazing also depends on how well-fitted your original windows are. As mentioned above, secondary glazing can be a good choice if your original single pane windows are in good condition.

However, if your original windows are warped or if the frames have separated somewhat from the walls of your home, secondary glazing is likely not a good option for you.

This is because poorly fitted single pane windows allow warm air to pass through the gaps between glass, frame and wall. In this situation, secondary glazing serves only to plug the gaps in your current windows; it adds very little extra insulating ability to your home.

Although it may cost more initially, removing your current windows and installing new double glazed ones will be much more effective in keeping your home warm and cutting your energy bills.


Making the decision

If you are trying to decide between secondary glazing and a standard double glazing installation, consider your budget, the condition of your current windows, and any building restrictions you may be subject to.

Also, however, bear in mind that you do not necessarily have to choose one or the other. It is perfectly appropriate, in some cases, to install standard double glazing in some windows and secondary glazing in others. You could consider installing double glazed windows in, for example, north-facing windows only, in order to maximize those windows’ insulating abilities.

Or, you could consider installing secondary glazing over your windows and double glazing for your verandah or conservatory doors. Arm yourself with enough information about the advantages and disadvantages of each option, and make the choice that’s right for you.

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