Secondary glazing is the next best thing to having real double glazed units installed. There might be any one of many different reasons why you want to use secondary glazed units. Maybe, you have perfectly good window frames and don’t want to rip them out yet. Or, perhaps you live in a listed building or conservation area and aren’t permitted to change the look of your property’s windows. Or, finally, maybe you just haven’t saved up enough money yet, but want to have some savings on your energy bills in the meantime.
On average, typical secondary glazing costs in the UK work out to be about £1250 to £1800 for 4 windows. Or, £5000 to £6000 for 15 windows. So, not only are the purchase and installation costs lower than fitting double glazed units, you don’t have to remove perfectly good window frames either.
There are many reasons why someone might want to install secondary glazing windows. You might want soundproofing or draughtproofing, without removing awkwardly located or particularly beautiful period windows. Don’t forget that local authorities can be very demanding if you live in a listed building. And, you’ll be expected to put up with cold and noise for the privilege of living in one of those cold and damp properties. Fortunately, as long as you don’t permanently alter the exterior look of your windows, secondary glazing will usually pass their requirements.
Secondary Glazing Prices List
Usually, the cost of installing secondary glazing depends on the number of windows, their style, and types. But we’ll talk more about these later on. For now, let’s look at the installation prices in more detail. The figures in the table are an indication of costs only. Remember that the purchase prices will vary with the size of each window. So, as a guideline, we’ve based the materials on an average price of £300, while the labour is £50 per window. All prices exclude VAT.
|No. of windows||Purchase cost||Labour cost||Total cost|
|Bungalow – 6 windows||£1800||£300||£2100|
|Victorian terraced house – 10 windows||£3000||£500||£3500|
|Typical semi–detached house – 12 windows||£3600||£600||£4200|
|Detached house – 16 windows||£4800||£800||£5600|
There are two ways to reduce labour costs.
- The fitter will probably give you a better rate if you have more windows to install.
- If you’re handy with a drill and screwdriver, you can remove the labour charges completely by doing the work yourself. Secondary glazing is very easy to install, and if you can DIY, you can have a go.
Don’t forget, the labour rates will be more expensive in London and the Southeast. Probably, between 10% and 20% higher than in rural areas.
What is Secondary Glazing?
At its simplest, secondary glazing involves adding an extra pane of glass within a suitable frame (the secondary window) and somehow fixing the frame to the existing window (the primary window). Sounds simple, doesn’t it? And it is, except that you have a few things to consider.
The effectiveness of your double glazing depends on a gap trapping still air between primary and secondary windows. The gap should be deep enough to hold a reasonable thickness of insulating, still air. While preventing the trapped air from convecting heat across the gap. Usually, in practice, the distance will be between 70mm and 200mm, but gaps smaller than that will be better to prevent convection currents forming within the gap. Another factor to consider is the phenomenon of resonance. If both primary and secondary panels have the same thickness glass, then sound from one pane will cause the other pane to resonate. Effectively, cancelling out any sound insulation properties.
Types of Secondary Glazing
The weather isn’t cold all year round, and sometimes you’ll want to open a window to allow some fresh air into the room. Therefore, the secondary glazing must be easy to open as well. There are a few ways of doing this.
Side hung single pane
This is basically one window next to another window. There’s a fixed frame within the window reveal, and a hinged secondary casement, opening inwards into the room. It has a latch just like any other window, and probably a ‘stay’ to prevent it from blowing open or shut. This has the advantage of allowing the primary window to open as well.
Side hung on a sash window
A typical sliding sash window consists of two windows in the same frame, sliding past each other vertically. The mechanics of the system allow either the top half or the bottom half to be open. Never both. A side hung secondary casement window completely covers the primary sash window.
Vertical slider against sliding sash windows.
Because the primary sliding sash windows meet and overlap slightly using a horizontal bar in the middle of the frame, it makes sense to have a similar setup with the secondary windows. You could say that this is simply a set of secondary sliding sashes inside the primary sliding sashes. Using these won’t be noticeable from outside.
Horizontal sliding windows
These are the same as vertical secondary sliders except they pass each other horizontally. These can be used for primary casement windows and sliding sashes.
Types of Removable glazing
If you don’t intend opening windows often during the winter, you could opt for this type. These are secondary frames fixed either directly to the primary windows or fixed inside the primary window’s reveal. But, they’re easy to remove if you want to.
Common methods include fixing sheets of polycarbonate, acrylic or Perspex plastic using double–sided adhesive tape or self–adhesive magnetic seals. The magnetic strip sticks onto the removable secondary frame and self–adhesive steel tape onto the fixed primary frames. Let’s look at each method in turn and discuss the pros and cons
Magnetic secondary glazing
As we said before this type uses magnetic strips or seals that fix to the secondary pane with steel tape fixed onto the primary. When in place, the magnetic seal prevents any air from escaping between the panes. So, this in turn keeps a stationary air gap between primary and secondary. Hence, good insulation. When they aren’t needed, you just pull the secondary pane away from the steel contacts and pack the secondary pane somewhere safe.
- This method is relatively cheap to buy.
- And, even cheaper to install.
- Even if you haven’t any DIY skills, everyone can use a pair of scissors to provide a low cost and lightweight method of double glazing.
- If they become damaged, then they’re easy to replace.
- Probably the biggest thing against this type is that it looks cheap. The panes will be thin and flimsy, and, will be very prone to scratches and dents. Especially when you want to store them away during the summer.
- Because you’re using weak magnetic contacts, the pane could easily come loose. Maybe because of a strong gust of wind or continual draughts.
- If the windows are exceptionally draughty, the pane will continually flex and flap, causing unnecessary noise.
- Distortions in the secondary pane will cause convection currents to start up between the two panes preventing insulation and causing condensation. The flexing will also work the magnets loose and the secondary might fall onto the floor.
Temporary Secondary Glazing
This isn’t a particular material. Instead, it refers to any method of providing a simple and lightweight pane fitted to the primary window using adhesive tape, magnets, clips or buckles.
- Good if you want a short term and low–cost option. Perhaps, you intend having all the windows replaced over a few months. Maybe, you want something to place over the existing windows while you wait for the job to start.
- Easy to fit, especially if DIY isn’t your thing.
- Doesn’t cost as much as full double glazing or semi-permanent glazing.
- If you intend using it for the entire house, it’s a substantial investment that might be better put towards a more permanent method.
- Can be difficult to access your windows for cleaning.
- Awkward if you want to open your windows on a bright sunny day in winter.
- Storing the temporary glazing panes somewhere safe might be a problem.
Secondary Glazing Film
The film is a thin clear plastic film that adheres to double–sided adhesive tape already stuck to the surface of the window frame. Once unrolled and in place, you heat the film with a hairdryer to stretch the film tight.
- Very cheap alternative to more permanent secondary double glazing.
- Very easy to install. Almost anyone can do it.
- Surprisingly this method works quite well with good insulation performance and reduced condensation.
- It looks cheap.
- If you aren’t careful, dirt can accumulate under the edge of the film on the adhesive tape.
- Over time, the film can start to sag.
- There is no sound insulation at all.
- You can’t temporarily remove the film. Once removed it must be disposed of.
Wooden Secondary Glazing
This method uses wooden frames in which you place the secondary pane. The wooden frames are then either screwed or clipped into position.
- There are many different styles of framing available.
- Can choose the profile shape and colour to match your primary glazing.
- Looks sophisticated with a heritage appeal.
- The wood will be bulky and might interfere with fastening the primary windows.
- Needs a lot of maintenance. Just like wooden windows, they will need regular repainting.
- Over time, the wood will warp and distort caused by expansion and contraction.
Semi-Permanent Secondary Glazing
Pretty much the same as temporary secondary glazing but more long term. The frames are constructed in such a way as to make it convenient to install the secondary frames in winter and remove them in spring.
- Generally, they are low cost.
- But, will look reasonably sophisticated if built properly.
- These are a long term solution to insulation around windows.
- Difficult to access the primary windows. You would be surprised how easily a small flying insect can crawl into the gap. But you’ve no way to remove it.
- It’s not easy to re-install the panels if you experience a cold spell after removing them.
- It’s easy to damage the secondary panels once removed.
- Difficult to store the panels through the summer.
Aluminium Secondary Glazing
This is a method of constructing secondary glazing units using aluminium frames rather than wood or uPVC. This is probably the best secondary glazing type when compared to the others mentioned here.
- Aluminium is strong and durable.
- The frame doesn’t have to have a large cross–section owing to aluminium’s inherent strength. Therefore, it’s not bulky.
- Aluminium can have a variety of colours and finishes to complement your existing décor.
- No need to paint it if you don’t want to.
- These are more expensive than wood or uPVC.
- Preferable for a professional or someone with good DIY skills to fit.
Secondary Glazing Benefits
Secondary glazing has benefits, over and above those of replacement double glazed windows. We’ve already touched on a few but now we have an opportunity to go into them in a bit more detail.
Planning authorities are very strict about altering the facade of certain buildings. Usually, a listed building in common use as a dwelling has interesting architectural features, meant to be preserved. This means you cannot change the look of it without written permission from the local authority. Unfortunately, the local authority will have removed your permitted development rights by issuing an ‘Article 4 Directive’. So, certain modifications such as double glazing, that are allowed for a normal dwelling place will not be acceptable in a listed building. This can make life very uncomfortable when we want to include modern energy–saving features such as double glazed windows. Instead, the authority allows you to use secondary glazing for listed buildings, as these fit on the inside of the windows and aren’t visible from outside.
Of course, it’s not only heat we want to save. If you live next to a busy road or railway line, you’ll need your secondary glazing to help with sound insulation too. Although standard glass or plastic will help a little with this, it’s much better to use acoustic glass, designed specifically for that purpose. Even a small reduction in sound intensity, say 10dB (decibels) which doesn’t sound a lot, actually means the volume has been halved.
Difficult to replace windows
Your windows might be in an awkward location and difficult to remove or replace. In cases like this, it’s fine to install secondary glazing. Also, if in the future, you no longer want the secondary panes in place, they are easily removed.
Sometimes noisy workshops have offices that need to be insulated against sound as well as having windows to let light through. Use secondary panes on these too.
Many old houses have windows that let draughts through. Secondary glazing effectively seals off the rest of the room from these.
On average, secondary glazing can work out to be less than half the cost of even the cheapest double glazing units. And, there’s little or no labour costs either. Furthermore, there won’t be any waste generated unlike removing old windows and replacing with double glazed units.
Many secondary glazing units contain toughened glass, which makes it very difficult for a prospective burglar to enter your home. They would have two windows to breach, not just one.
One of the big advantages of having secondary glazing over double glazed units is that there is much less disruption and mess.
- No-one removes anything.
- You don’t have to put up with howling gales through the house while they put in a new window.
- There’s no masonry mess or dust, and no making good afterwards.
- There’s no need to comply with building regulations.
Historic England produced a booklet entitled Energy Efficiency and Historic Buildings (secondary glazing for windows) to explain about secondary glazing in a listed building. It’s well worth a read if you’re interested in this type of glazing. As often, secondary glazing is the only type of heat retention possible in period properties. In the booklet, they state that a window with a single glass pane has a heat loss value of about 5.4W/m2K. But, when you attach a secondary glazing unit and use low emissivity glass, you can reduce heat loss to about 2.0W/m2K. That’s a reduction of more than 60% compared to a single pane. They also state that the optimal gap should be about 16 to 20mm. But in practice, this isn’t always possible.
Double Glazing vs Secondary Glazing Options
We‘ve already discussed the pros and cons of secondary glazing so won’t go any further here. Except to say that both methods have their uses, can significantly improve thermal efficiency and are widely available for the general public. Having said that, double glazing with wood, aluminium or uPVC frames must be installed by a professional window fitter, who ensures compliance with the UK Building Regulations. However secondary glazing doesn’t require the Building Regulations so can be fitted by a window fitter, a handyman or as a DIY project.
Double glazed units are much more efficient than secondary glazing. The gap between the two glass panes is hermetically sealed and filled with an inert gas such as argon. This is better than the air used in secondary glazing because it’s a better insulator with thermal conductivity of 67% that of air.
Although Historic England states that the optimal gap between primary and secondary windows should be between 16mm and 20mm, this isn’t always possible. In practice, we are limited by the construction of the primary window and how deep the frames are. It is a matter of doing the best we can to compromise and have the secondary pane as close to the primary as possible.
DIY Installation: Should You Consider It?
If you’re okay with DIY, then you’ll find no problems installing secondary glazing. You’ll need simple tools that you’ll probably find in your toolbox. The method used will vary depending on the type of secondary glazing you choose. But, let’s assume we’re installing the magnetic fixing system mentioned earlier.
- Measure the width and height of the glass pane.
- Add 25mm to each measurement to give the size of the plastic sheet needed.
- Trim the plastic sheet to this size using suitable cutting tools. A padsaw, hacksaw or very fine tenon saw are probably the best tools as they all have small and fine teeth. Use the saw at a shallow angle and don’t press. Let the weight of the saw do the cutting.
- Smooth the edge with fine sandpaper and wipe away any bits of plastic still left on the sheet.
- Take the coil of self–adhesive magnetic strip and stick along each edge. Peel off the protective paper as you go.
- Hold the panel so it overlaps the window evenly all the way around. Use a pencil to lightly draw a line around the edge.
- Fit the self–adhesive metal strip to the window frame using the pencil line as a guide. At the corners use some heavy–duty scissors or tin snips to cut the strip to length.
- Next, clean the window and wipe away any condensation. Also, use mild detergent and water to wash all grease from the secondary pane.
- Press the sheet against the primary frame allowing the magnet to stick to the metal strip.
If you have a large window to cover, say 1200mm x 1200mm or more, the magnets might not be strong enough to hold the weight of the panel. If this is the case, use plastic securing clips to take the weight.
Secondary Glazing FAQ
Does secondary glazing reduce condensation?
Secondary glazing will reduce condensation but won’t completely prevent it. This is because the air gap between the primary and secondary isn’t airtight and is filled with moisture–laden air.
How do I clean the inside of my secondary glazing?
Use a vacuum cleaner and a soft brush to remove grit and dust. Then use a damp cloth and a detergent with a neutral pH to remove any grease marks. After washing, dry with a lint–free cloth.
How do you remove secondary glazing?
This depends on which type you’ve used. Magnetic fixings just need you to pull the secondary panel away from the primary window frame.
However, always follow the manufacturer’s instructions, which will give guidelines on how to remove secondary panels in the easiest possible way without damaging anything.
Get Quotes From Window Installers
If you cannot use double glazed units to reduce heat loss in your home. Don’t worry too much. There are many different types of secondary glazing methods available to suit almost any type of fixed window. Although you can do this yourself as a DIY project, it might be quicker and easier to call in a professional to do the job.
If you want to know the cost of secondary glazing for your house, complete the form at the top of the page and you’ll receive 3 or 4 quotes from people who know what they’re doing.