A double glazed unit (also known as double glazing or insulated glass units) are a type of window or glass panel that consists of two panes of glass separated by a sealed air or gas-filled space. This space serves as an insulating layer, reducing the transfer of heat between the inside and outside of a building.
The two panes of glass are often coated with a low-emissivity (low-E) coating, which further reduces heat transfer and improves energy efficiency.
Double glazed units can also help to reduce noise transmission and improve security, as they are more difficult to break than single-pane windows.
They are commonly used in residential and commercial buildings to improve energy efficiency and comfort.
Double glazed unit or double glazing
‘Double glazed unit’
The terms “double glazed unit” and “double glazing” are often used interchangeably, but they can have slightly different meanings.
A double glazed unit refers specifically to the sealed glass unit itself, which consists of two panes of glass separated by a sealed air or gas-filled space.
The term “double glazed unit” is commonly used in the glass and window industry to refer to the individual components of a double glazed window or door.
‘Double glazing’
On the other hand, the term “double glazing” can refer more broadly to the installation of double glazed units.
In this sense, “double glazing” encompasses not just the glass units themselves, but also the frames, seals, and installation methods used to create a complete double glazed window or door.
So, while the terms are often used interchangeably, “double glazed unit” typically refers to the glass unit itself, while “double glazing” can refer to the entire window or door system.
Where to buy double glazed units?
Double glazed units can be purchased from a variety of sources, including glass and glazing companies, window manufacturers, and home improvement stores.
Here are a few places where you can buy double glazed units:
1. Glass and Glazing Companies
Many companies specialize in manufacturing and installing double glazed units for windows and doors. These companies often have a wide range of glass types and thicknesses to choose from, and can provide custom sizes and shapes to fit specific window or door frames.
2. Window Manufacturers
Some window manufacturers offer double glazed units as a component of their windows or doors.
If you’re in need of new windows or doors, you can often order them directly from the manufacturer with double glazed units already installed.
3. Home improvement companies
Many home improvement companies carry pre-made double glazed units that can be installed into existing windows or doors.
These units are often sold in standard sizes and thicknesses, and may not be customizable to fit non-standard frame sizes.
When purchasing double glazed units, it’s important to consider factors such as the thickness and type of glass, the gas filling used, and the quality of the seals and frames.
It’s also important to ensure that the units meet any relevant building codes or energy efficiency standards in your area.
Buying units or the full frame?
It’s generally not common or practical to purchase just the sealed glass unit without the window frame, as the frame is an essential component that holds the glass in place and provides structural support.
In most cases, double glazed units are purchased as a complete window or door system that includes the frame, sash, hardware, and other components necessary for installation.
That being said, there are a few situations where it might make sense to replace just the double glazed unit.
For example, if the window frame is still in good condition but the glass has become damaged or fogged due to a broken seal, it may be possible to replace just the glass unit while leaving the existing frame in place.
However, this is generally a job that should be left to a professional glazier.
Installation and double glazing
We have a fully dedicated page for double glazing as well as other feature pages on Bi-fold doors, tilt and turn windows and installer information.
However if you are looking for double glazing quotes? Just fill out the form and we will do the rest.
Double glazed unit costs
The cost of double glazed units in the UK depends on a few factors, but on average:
- For a standard 1.1m x 1.5m double glazed unit, expect to pay £80 – £120
- Larger units around 2m x 1.5m can cost £150 – £200
- For custom shaped or extra large units, prices range from £200 – £300+
- Additional features like toughened glass, argon gas filling, thermal coating etc can add £50 – £100 per unit.
- Triple glazed units are 50-100% more expensive than double glazed.
- Installation costs are extra – typically £150-£250 per window assuming a straightforward replacement job.
So for a typical small 3 bedroom house needing 5-7 double glazed units replaced, total supply and installation costs would likely be in the region of £1,000 – £2,000.
Always get multiple quotes for an accurate price. Replacing just the glazed units can be a cost effective way to improve thermal efficiency compared to full window replacement. Make sure to check the window frames are still structurally sound first.
There is a difference in cost between just purchasing replacement double glazed units vs having them professionally installed:
Purchasing Double Glazed Units
- This just covers the supply of the glass units to your specification.
- No installation or additional work is included.
- Prices start from around £80-£150 for standard sized units.
- You’ll need to source and pay an installer separately if needed.
Getting Double Glazed Units Installed
- This covers not only the supply of the units but also the installation.
- An installer will remove old glass, fit the new units, seal, testing etc.
- Total costs start from £250-£350 for basic installation of a standard unit.
- Installation typically costs £100-£150 per window on top of the double glazing unit price.
- Extra costs may apply for non-standard jobs e.g. listed buildings.
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Glazed unit FAQ’S
The gap between the glass panes in a double glazed unit is typically 12-20mm, although it can vary depending on the manufacturer and specific product.
In most cases, it is not possible to repair a broken double glazed unit, and it will need to be replaced. However, some companies may offer replacement glass panes for certain types of units.
A sealed unit is a double glazed unit where the air gap between the glass panes is sealed and filled with an insulating gas, such as argon. An unsealed unit is a single pane of glass without an air gap.
The U-value of a double glazed unit measures its thermal insulation properties, and is typically between 1.2 and 2.8 W/m2K. A lower U-value indicates better thermal insulation.
