Double Glazing vs. Secondary Glazing

Over the years, Double Glazing has replaced Secondary Glazing in many homes. This is due to its improved performance, especially in terms of thermal and sound insulation. Double glazing is a type of glass that consists of two layers placed side-by-side and separated by an air space whose width generally varies between 6 and 16 millimetres. Its insulating performance attracts many homeowners looking to boost energy efficiency of rooms or Conservatories.

Get a FREE No Obligation Quote NOW!

It is important to know how to distinguish between the two options.

Secondary glazing

This variant consists of a single layer of glass. In most cases, the glass plate has a thickness of 4 to 6 millimetres but it can also be thicker. In terms of insulation, its performance is average. The coefficient of thermal transmission is an indicator that makes it possible to establish the insulating quality of a window. The lower this coefficient, the better insulation provided by the glass. Secondary glazing has a coefficient of 6 W/m²K, which is significantly high.

Secondary Glazing

Double glazing

Double glazing has better insulating qualities than secondary glazing. It has two layers of glass separated by an intermediate space called an air gap which is typically filled with Argon gas. This gas is an excellent insulator and its presence between the two plates enhances insulation, which surpasses that of secondary glass.

Double Galzed Window

Energy efficiency

Double glazing has a thermal transmittance (U-value) of about 2.8 W/m²K, which represents insulation that is at least twice as good when compared to a secondary glazing unit. By replacing the air gap with an Argon gas blade, it is even possible to obtain a coefficient of 1.3 W/m²K. Adding a layer of metal oxides on one of the inner sides of the double units further improves the thermal insulation to reach the U-value of 1 W/m²K.

Noise reduction

Apart from its thermal performance, Double Glazing is also beneficial in terms of sound insulation, which prevents occupants from hearing sounds emanating from outside. This is particularly useful in a big city where noise is an issue.


Double glazing comes with a slim, sleek profile, which makes it ideal for boosting the appeal of any building. This variant looks incredibly attractive whereas secondary glazing is a viable option for homes in conservation areas where an authentic look must be maintained.

Get a FREE Quote

No Obligation, Quick & Easy

Get a Quote
25 Year Rosette

30 Years in Business

We are a family run business based in the Midlands for over 30 years.