5% Summer Discount - At The Plastic People we're offering a 5% discount across the whole store on orders over £100.00 plus VAT. To redeem simply add July2024 on checkout!

Secondary Glazing: A Buyers Guide

Written by PJ
26/10/2022 13:06:31


What is Secondary Glazing on Windows?

Keeping our homes warm during the winter months can be expensive. We turn up the central heating as high as it will go and keep it running for 24-hours a day - during a time when energy costs hit their peak. There must be a cost-effective way to keep the heat locked in our homes, right?

On average, 18% of all household energy is lost through our windows - that’s almost 1/5th of your heating gone to waste! A further 30% of heat is lost through draughts, and so making sure your home is well insulated is a sure-fire way to keep it both warm and lower energy bills. This is where secondary glazing comes in!

Secondary Glazing involves adding a thin second pane to your existing window. It is an almost unnoticeable addition to your home but is sure to pack a punch when it comes to improving heat retention. 

What does secondary glazing do?

Secondary glazing works in much the same way as double glazing. In adding another layer or pane to your existing window, you create a small gap that acts as an insulating barrier. This gap, created by the installation of secondary glazing, is a vacuum that slows the movement of heat from one side of your window to another. As the transfer of heat is reduced, your home will be warmer in the winter and cooler in the summer! 

Unlike traditional double and triple glazing, secondary glazing does not require entirely new windows and frames to be manufactured and installed. Instead, we use acrylic plastic (aka. Perspex and Plexiglas) as the insulating material. Acrylic is more cost-effective, lighter and easier to work with than glass and other glazing materials. Acrylic is also some ten times stronger than glass! 

This masterful piece of window insulation has some other uses too: 
• Additional window panels also make your home more secure as it is harder to break through multiple layers of either glass or plastic. 

Is secondary glazing more effective than double glazing?

The simple answer is: yes, secondary glazing is more effective than double glazing at keeping your home warm. On average, double glazing reduces heat loss in the home by up to 55%. That sounds impressive, but magnet-strip secondary glazing can go further and reduce heat loss by up to a massive 63%! 

Not only is secondary glazing a more effective form of insulation than traditional window glazing, but it is more cost-effective too. Installing double or even triple glazing throughout an entire home can cost an absolute bomb - the average quote ranges from £3,000 to £7,000! Secondary glazing is 15 times cheaper than double glazing, and could you save you thousands of pounds! 

It is worth keeping in mind, however, that not all forms of secondary glazing will be more effective. For instance, secondary film glazing, which involves sticking a thin adhesive sheet to the inside of your window, does not offer great levels of heat retention. Therefore, we recommend opting for a permanent or semi-permanent form of glazing, such as magnet-strip glazing.

Does Perspex secondary glazing work?

When it comes to choosing your secondary glazing, there are a few options available to you. Most commonly, customers opt for either magnet-strip secondary glazing - which is made using Perspex (acrylic) plastic - or a plastic film glazing. Perspex secondary glazing is the most effective of these options as it offers the highest levels of insulation. 
Magnet-strip glazing is a system whereby you use two magnets to attach an additional sheet to your existing window. This creates a seal that reduces the amount of heat transfer. While secondary glazing film involves sticking an adhesive sheet to the inside of your window. This offers only limited insulation, but it is the cheapest option at £2 per window sheet. 
As we mentioned previously, Perspex secondary glazing works just as well, if not better, than traditional uPVC double glazing techniques, but at a cheaper price bracket. Other secondary glazing options include aluminium and wooden framed glazing - but these can be costly and less effective alternatives. 

Does secondary glazing insulate? 

Secondary glazing is a cost-effective method of window/glass insulation. By adding a slim, additional layer to your windows, you can create a gap that acts as a vacuum. This vacuum reduces the amount of heat transfer that can take place, keeping your home warmer in the winter and cooler in the summer. 
We recommend that the gap between your existing window and secondary glazing panel is between 100mm - 200mm thick. A gap of this size will ensure optimum performance in terms of both heat retention and sound reduction. 

Can you open windows with secondary glazing?

You can continue to open and close windows even after secondary glazing has been installed. Plastic glazing panels can be cut to any size or shape, making them the perfect fit, no matter the design of your windows.

Remember to request any cut-outs you made need to accommodate the handles or hinges of your windows - manufacturers will be able to work from your designs and specifications. If you have a sash window that opens vertically, you will need to install sliding secondary glazing panels - but we will discuss in-depth a bit later in this guide. 

Does secondary glazing stop condensation?

Secondary glazing works to help reduce the build-up of condensation in your home. The addition of a slim second window pane helps create a seal that minimises air leakage - this means that the surface temperature of your windows will be greater, decreasing the chance that condensation can form. Reducing condensation in your home is ideal to prevent things such as damp and mould from forming on your walls and ceilings. 

Do you need planning permission for secondary glazing?

Unlike double and triple glazing, you never need planning permission for secondary glazing. This is why secondary glazing is becoming incredibly popular with homeowners who live in locally listed areas and heritage sites. 

Many types of secondary glazing can be removed at any time, making it a non-permanent solution to eliminating draughts. This flexibility allows you to forgo the trials and tribulations of applying to the local planning office, saving you both time and money! 

As a result, secondary glazing is also the go-to home insulation solution for those who have sash windows and other types of frames, which use sliding systems instead of hinges to open.

Is secondary glazing safe?

Secondary glazing is incredibly safe. Adding a second pane to your window provides an additional layer of security to your home. The plastic used for secondary glazing is also child-safe and hygienic. Acrylic can easily be wiped clean using a cloth and warm, soapy water. 

All types of window glazing and insulation are made from durable materials. For instance, acrylic is typically around ten times stronger than glass and shatterproof, which means if it does break, it will snap into a few large and dull pieces instead of lots of tiny, sharp fragments.

How long does secondary glazing last?

The lifespan of your secondary glazing depends on the material you use. For instance, both the Plexiglas and Perspex brands of clear acrylic plastic (which we use in our MagnetGlaze kits) are guaranteed to last at least 30 years before any discolouration or warping occurs. 

Typically, double glazing lasts between 10 and 25 years, and so your window is likely to last longer if you opt to use a secondary glazing method. Adhesive film glazing does, however, have a very short lifespan as it can bubble and warp under extreme heat. We recommend only using plastic film as a temporary glazing measure before changing to a magnet-strip type.

Can you secondary glaze sash windows?

If you live in an older property - particularly one that has been locally listed or is in a conservation area - you will likely have at least some sash windows in your home. Depending on local planning laws, you may not be able to replace these with modern double glazing options. However, do not fret, you can secondary glaze sash windows!

Sash windows do not operate on a hinge but slide open, either vertically up and down or side-to-side. These windows typically have only a single pane, and so they are not very energy efficient. Nevertheless, as they can open so wide, they offer great options for ventilation in the summer months.

What is secondary glazing for sash windows?

Similarly, to secondary glazing for regular windows on a hinge, you can install secondary glazing for sash windows by inserting a slim additional Perspex or acrylic panel. You can continue to maintain the traditional look and shape of sash windows even when installing secondary glazing, but the panels will need to be housed within a sliding frame so they can move with the existing window pane.

As a result, the seal will not be as tight as in other forms of secondary and double window glazing, but you will still receive the benefits of a warmer and less noisy home! Secondary glazing on sash windows is still a DIY task and can be done at a low cost.

How do you measure secondary glazing?

Your measurements must be accurate when purchasing and installing secondary glazing; otherwise, you will not achieve a tight seal, and the performance of your glazing will be lessened. 

When installing magnetic secondary glazing, instead of measuring the glass pane edge-to-edge, you need the plastic panels to overlap with the frame slightly. Standard magnet-strip tape, which you use to secure the glazing, is 15mm wide - this means your plastic needs to overlap with the frame by 20mm to ensure it lines up with the positioning of the tape. 

Leaving some overlap also means that it will be easier to remove the glazing, if needed, as you can fit your fingers around the edge of the plastic. If you are using extreme tape, which is 25mm wide, you should leave around 30mm excess on each side. 

Depending on the size of your window, we recommend purchasing different thicknesses of plastic to ensure that your glazing does not warp:

•    For panels with a perimeter less than 4500mm, use 3mm plastic and standard tape. 
•    For panels with a perimeter greater than 4500mm, use 4mm plastic and extreme tape.

When purchasing any type of magnet-strip tape, make sure you purchase enough rolls. You need the tape to run along every edge of the glazing. So, add up the total perimeter of all the panes you are going to purchase and this will determine how much tape you need. Our MagnetGlaze tape comes in two sizes:

•    A standard tape (15mm thick) comes in 5-metre rolls. 
•    Extreme tape (25mm thick) comes in 10-metre rolls.

How much are secondary glazing units? 

The price of secondary glazing units varies, depending on the type you choose. Obviously, permanent double glazing is the costliest option as it requires an external team to manufacture and install your new windows, while DIY alternatives such as magnet-strip glazing are substantially cheaper. On average, secondary glazing units are 15 times cheaper than secondary and triple glazing. 

Here’s the price breakdown per square metre to give you an idea of costs:

•    Double Glazing: £300 per square metre
•    Triple Glazing: £400 per square metre
•    Magnetic Secondary Glazing: £35-45 per square metre 
•    Secondary Glazing Film: £3-4 per square metre

Magnetic secondary glazing offers similar levels of insulation and noise reduction as double glazing, but is, on average, 1/10th of the price! You will also save on labour costs as magnet-strip, and other types of secondary glazing installation can be completed as easy DIY projects over a weekend. 

Here at The Plastic People, we offer complete magnetic secondary glazing kits to help you keep your home warmer for less. You can get an instant quote today by entering your measurements into our online calculator. 


View All Blogs

Other Blog Posts

Secondary glazing adds an additional layer of protection for you and your home by placing an insulation barrier between your home and the window. By adding this extra layer, secondary glazing keeps the inner panel warmer and reduces condensation formation.
Published 29/04/2024 15:36:12