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Retain Warmth and Reduce Heat Loss with Granada’s Secondary Glazing

Jan 9, 2019 | News |

Slimline secondary glazing is rapidly growing in popularity as homeowners are requesting to have it installed to increase thermal insulation. Increasing thermal insulation will lead to lower energy consumption and reduced energy bills as it makes homes warmer.

It is often advertised that secondary glazing can decrease heat loss by as much as 65%, we would like to share with you why the installation of secondary glazing can minimise heat loss and what we would recommend to achieve optimum thermal insulation.

Windows of any type will let heat and warmth escape, by adding an additional barrier, secondary glazing can prevent heat loss and draughts.

Listed status can prevent or make it difficult for windows in conservation areas to be changed, they are particularly susceptible to heat loss as the original glass is a poor insulator, also the aged window frames can let in draughts. Old UPVC windows can also lose heat, the double-glazed glass panes can become compromised and leak gas which was put there to prevent the heat loss in the first place.

Modern secondary glazing is slimline, durable and discreet. Granada’s bespoke secondary glazing is found in all property types as it is a superb heat insulator, it also mutes noise and substantially increases security.

What is Secondary Glazing?

Secondary glazing involves fitting a discreet internal window in addition to your existing, single, double and triple glazed window. It’s a cost-effective and efficient way to insulate and soundproof your windows and preferred for the use within Listed Buildings and conservation areas.

What are the main benefits of installing Secondary Glazing?

  • Up to 80% noise reduction
  • Minimise drafts, reduce heat loss by up to 65%
  • An additional security barrier
  • Condensation control
  • Reduced carbon footprint and energy bills

How much heat can I save?

Firstly it is essential to understand how do we measure heat loss? heat loss is measured as a number and is expressed as a U-value. U-values measure how effective a material is an insulator where a lower U-value means that the material is an effective thermal insulator.

As an example, the table below highlights that a single glazed primary window has a U-value of 5.7W/m2K. When secondary glazing is installed with 6mm toughened glass and a low-E coating, the U-value decreases to from 5.7W/m2K to 1.87W/m2K. This decrease is an astonishing 69% decrease in heat loss through the window.

Decreasing heat loss and blocking draughts will naturally lower your homes energy consumption leading to reduced energy bills. Through reducing heat loss and keeping your home at a constant temperature prevents boiler overuse and once a room is heated to the desired temperature, the boiler will turn off until needed.

Heat can be lost through the glass pane or unsealed frames, also cold draughts will penetrate the smallest of holes in the window frame introducing cold air into your home. Installing secondary glazing gives your home an additional barrier to prevent draughts and cold air breaching your windows.

The example above highlights what heat savings can be expected if you have a single glazed primary window, as mentioned above, secondary glazing can and is installed in conjunction with double glazing. The table below demonstrates secondary glazing’s thermal enhancements with double glazing.

Installing Secondary Glazing for Optimum Thermal Insulation

For optimum thermal performance, Granada Glazing recommends that the secondary glazing is fixed at a distance no greater than 80mm away from your primary glazing glass. This 80mm “air cavity” creates an insulating pocket of air between your primary glazing and secondary glazing, this will act as an insulator substantially decreasing heat loss. The secondary glazed unit can be installed into the window reveal and will sit on your window sill, this type of installation is commonly referred to as “reveal fix”.

What is Low-E glass?

Speciality glasses have been designed to offer exceptional thermal performance where most commonly a glass with a low-E coating is installed to decrease heat loss. Low-E (Low Emissivity) coatings have been designed and developed to reduce the amount of ultraviolet and infrared light that passes through the glass. As warm air from inside the room hits the glass the low-E coating will reflect the heat back into the room preventing the heat and warmth escaping. The coatings are thinner than a human hair and do not compromise the amount of light that is transmitted through the glass. In most cases, we would recommend that a 6mm toughened glass with a low-E coating will yield the best performance.

Can Secondary Glazing have a double glazed sealed unit?

The table above demonstrates that a secondary glazing system installed with a 28mm double glazed unit can achieve a U-Value of 0.8W/m2K. Granada Glazing has designed and manufactured a heritage hinged unit which can be installed with a 28mm double glazed sealed unit. The hinged unit operates on hinges and matches the function of any casement window. For more information on Granada’s hinged units, please click here.

In Summary…

Secondary glazing acts as an excellent thermal insulator and can help seal in the heat and reduce energy bills. For optimum thermal performance, we advise that the secondary glazing is installed with a 6mm toughened glass and low-E coating. Install the secondary glazing no greater than 80mm from your primary glazing glass.

Granada Glazing design, manufacture and install bespoke secondary glazing to give an exceptional thermal and acoustic performance. We often help homeowners, and commercial contractors in all sectors and building types achieve a look, function and the highest performance standard.

All secondary double glazed windows are manufactured in the UK at Granada Glazing’s 40,000 square feet manufacturing facility. We use state of the art CNC machinery to cut our unique aluminium profile, this ensures total accuracy and prevents holes and gaps for either noise and cold draughts to penetrate. Finished in over 200 RAL colours you can select a colour that will complement your modern or traditional home. Granada’s secondary glazing is slimline durable and discrete and is offered with a five-year guarantee.

For more information on how secondary glazing will create a warm, peaceful and secure home please telephone 01909 499 899 or email:

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