10 Key Questions About Double Glazing Answered

If you live in the UK you’ll be more than familiar with the unpredictable British weather. Our unique weather means it could be sunny one minute and howling with wind and rain the next. It’s because of this temperamental climate that our obsession with windows is almost as intense as our obsession with the weather. You’d think that replacing your old windows with a nice new set would be a simple process, but actually there is so much choice it can be somewhat of a minefield. The reason Sash Windows London Ltd have such a good reputation is because we try to cut through the jargon as much as possible for our customers. We take all things into account such as location, budget, type of property etc and find the best solution which is tailored for each and every customer.

With this in mind we’ve decided to answer 10 key questions about double glazed sash windows. You might wonder if double glazing is the best choice for your property. You might wonder about the benefits or possible disadvantages, and whether double or triple glazing would be better. If you are pondering over whether to get double glazing fitted, then read on as hopefully you’ll be a lot more informed by the time you’ve finished reading this page.

PVCU Heritage Double Glazing

1) What is Double Glazing?

Double glazed windows were invented by C D Haven in America in 1930. There were extremely expensive to produce back then, but have seen a steady growth, and are now very popular within the United Kingdom. The idea behind the invention was simple. Two panes of glass offer better protection than one. Today, double glazed windows are also called Insulated glazed windows (IG) or, sometimes, double-pane, or triple-pane for triple glazed windows. They consist of window panes separated by a space that can act as a vacuum and be filled with gas such as argon or krypton. Double glazing is the most effective method to reduce heat loss from buildings and houses, which is why they’re so popular in the UK.

2) What’s wrong with single glazed windows?

If you are considering replacing your old windows, or installing windows for a new property, then you might want to take into account the common problems that can be found with single pane windows. There is nothing inherently wrong with single paned windows, and they still serve their purpose, but single pane windows can include heat loss, noise and condensation.

Common Problems With Single Glazed Windows

Energy Efficiency

A typical domestic building loses 10% of its heat through the windows and a standard window loses 2/3 of the energy through radiation because of the glazing. This heat loss is expressed by a U- value, which is the thermal transmittance of a glazing unit. Single glazing has a U- value of 5.6, double glazing of 2.8 and triple glazing of 0.8.
If walls, roof and the floor of a house are insulated, but the windows are ignored, then cold spots will surround the windows and all the efforts to save money and heat will be in vain.


Living in a noisy area can be more than annoying. Studies have demonstrated that noise pollution has a wide range of negative effects on our health such as stress, sleep disturbance and even hypertension. Noise reduction is another problem you can solve through different combinations of pane thickness and extra glazing.

Damp, condensation and cold patches

When windows and doors are not insulated properly, warm, moisture-packed air can react with colder surfaces like walls and floors, and cause a cool down effect which releases small drops of water. The more the air is moisturised, the more likely it is that your home will get condensation, which can be bad for your health, especially if you are exposed to it for a long time.
Generally damp areas, cold patches and mould can appear inside and outside the house when ventilation, heating, and insulation are not adequate. This is usually when there is a greater difference between the temperature levels of the walls and the windows. The solution is to install efficient windows with a U- value similar to the walls, which is usually around 0.3.

3) Do I need planning permission for double glazing?

If you are considering double or triple glazed windows, then you won’t need to apply for any special planning permission. However, if your home is classed as a listed building it can complicate things, and you may find yourself restricted to using only single pane windows. Most heritage buildings were built before 1920 and their windows have never been replaced due to the regulations and conservation areas. If this is the case you may find you can only replace your existing windows on a like for like basis, and you’ll never be able to enjoy all the benefits that come with double or triple glazed windows.

Conservation Areas

When a building or area is of historic interest, it is considered to be a place of national importance and is added to the National Heritage List for England.
There are three categories:

  • Grade I for buildings of the highest significance.
  • Grade II* (5.5% of listed buildings)
  • Grade II (92% of listed buildings)

Listing implies extra restrictions on changes you might want to make to the building’s interior and exterior. Also, there is the possibility that your area is regulated by an Article 4 Direction and you will be required to get permission to change any windows or doors. Since the rules are different depending on the conservation area you live in, it is always important to contact the Local Authority before starting any work.

Remember to check with your local planning office, if:

  • You live in a conservation area.
  • You have an article 4 direction on your property.
  • You live in a listed building.

Improving energy efficiency in listed buildings is important because they were constructed with permeable materials that absorbed a huge amount of moisture, and this can damage either the building, or the occupants’ health. Unfortunately the rules surrounding listed buildings do not always make this possible.

4) What is triple glazing?

Triple glazed windows work on the same principle as double glazed windows, but they have three panes of glass instead of two. With more glass, and more intricacies involved triple glazed windows are more efficient than double glazed windows, but they are also more expensive.

5) Is triple glazing better than double glazing?

It depends how you define better. If you are thinking are they better at noise reduction, then yes they are. They are also better at insulation, but when it comes to value for money it depends a lot on where your property is located.

6) Should I choose triple glazing or double glazing?

The choice between double or triple glazed windows depends on where you live and what your needs are. If you live in an area with a lot of noise for example then triple glazing will reduce the impact felt within your home. But also, you might live in an area where triple glazing is prohibited, and you must choose double glazing. Sometimes even double glazing is not permitted and the ideal solution could be offered by secondary glazing. If this is the case, it depends on the characteristics of your house or building, your budget and the amount of insulation they need.
It is clear that triple glazing offers better insulation and protection from noise, but on the other hand it is heavier because of its three panes instead of two. Triple glazing is ideal for larger areas as it allows maximum glazing sizes with minimum heat loss. It also increases the acoustic performance of a window through improving sound insulation in the home.

7) What frames can I use?

Usually the options for frames are the same with double glazing as they are with triple glazing. At Sash Windows London Ltd we offer a wide range of styles and materials to choose from. See below for our different options and key benefits.

TIMBER : key benefits

  • natural appearance
  • renewable raw material
  • excellent insulator
  • durability

Timber has always been used as a window frame material ever since windows existed. Thanks to the natural appearance and excellent insulating properties of wood, timber is the best choice for listed buildings where only small modifications are allowed. Timber itself comes from renewable raw materials which make it environmentally friendly and can help to balance out CO2 levels. Our timber sash windows come in a range of engineered hardwood or redwood, to ensure strength and durability. They are then factory sprayed with micro-porous paint, and using this system we are able to offer a 10 year guarantee on the finish.

What is more, our timber products achieve the highest certification with The Forest Stewardship Council (FSC).

ALUMINIUM : key benefits

  • durability
  • easy care
  • modern look
  • eco-friendly
  • light weight

Aluminium is a material which offers strength and resistance to corrosion and rust. One of the most appreciated benefits of aluminium is without a doubt its durability. It can last decades with minimal maintenance and stays looking good in all weathers. Another reason why aluminium makes such a good choice, is that its eco-friendly, endlessly recyclable and sustainable. Its popularity has increased in recent years due to its stylish, modern look and its lightweight which makes installation easier.

PVCU : key benefits

  • easy care
  • long durability
  • very good insulation properties
  • versatility
  • many colours available
  • light weight
  • lower price
  • 100 % recyclable

There are many reason why choosing UPVC frames could be the ideal solution. Prices are lower and the windows durability is longer. The windows can be shaped in many different ways, some modern new builds and others that can be designed for strict conservation areas. Possibly the biggest benefit is that UPVC is better than aluminium in terms of insulation and it can last just as long, if not longer with very little maintenance. Furthermore, with special frame foils it is also possible to give UPVC the look of natural timber windows.

8) What else do I need to know about double or triple glazing?

A double or triple glazed sash window is more than just two or three panes of glass put together. Its components are made of different materials in order to satisfy different needs or requirements. The components you should look for are: the frame, the space between the panes, the gas filled within the space and the glass itself.

Pane spacers

A ‘pane spacer’ is the bar that separates the two (or three) panes of glass, and is filled with a desiccant that absorbs any residual moisture trapped in the gas space during manufacturing. This helps to prevent condensation when the outside temperature falls. Spacers are typically made of low heat-conductive material such as aluminium with a thermal barrier or foam.

Gas Fills

The cavity between the two panes of glass is filled with an inert insulating gas. Argon is the most common gas which ensures a longer windows effectiveness by preserving the metal parts from rust and corrosion due to oxygen present in the air. Since this gas is more viscous, heavier and denser than air, molecules can’t move quickly and this reduces heat loss and condensation. At Sash Windows we use A-rated argon gas.


The new legislation (The Government’s Approved Document L1B – Conservation of Fuel and Power in Existing Dwellings) has made the usage of so called Low E Glass or low-emissivity glass compulsory.

Its thermally insulating coating (metal oxide on one of the internal panes), reflects the long wave heat energy produced in our homes away from the glazing, and economises the heat loss from our buildings. At the same time, the metallic coating allows short wave heat energy to pass through the glass (known as the solar factor or solar heat gain) and heats our homes using the thermal energy from the sun.

Thanks to the most recent innovations in double glazing, today we can offer various solutions for energy efficiency, sustainability, comfort, security and design.

9) How much money can I save with double or triple glazing?

According to the Energy Saving Trust, there are big savings to be made from have double glazed windows installed.

Energy rating |  Detached Semi | Detached Mid Terrace | Bungalow | Flat
A Rated | £120 – £160 £85 | £110 £65 | £90 £55 | £75 £40 | £60
B Rated | 110 – £145 £75 | £100 £60 | £80 £50 | £70 £40 | £55
C Rated | 110 – £135 £75 | £95 £60 | £75 £50 | £65 £40 | £50

Sources and useful links


10) Your Question Here

If you’ve been paying attention this far you’ll probably have noticed that we have only answered 9 questions on our ’10 key questions’ list. This is because we ant you to ask questions that maybe we haven’t thought of. If you’re thinking of getting double, or triple glazed windows then we would love to answer your questions and provide as much help as we can. Join in the discussion and leave us a comment below with any questions you have, and we’ll endeavour to answer them as quick as we can.