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Secondary glazing can be defined as the installation of a fully independent window frame on the inside of an existing window.  These secondary glazed units are available in a variety of designs, including horizontal and vertical sliding, hinged casement, lift out and fixed.  The frames can also be shaped to fit any type of reveal design.   Although many homes have secondary glazing, because the home owner doesn’t want to or cannot replace the existing widows (e.g. listed building restrictions) many fit them for the variety of benefits that secondary glazing provides.

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Examples of where secondary glazing will be of benefit


Providing a second window behind the existing one clearly provides some additional security against burglary.  If you live in a building that has planning restrictions that prevent you from replacing the existing widows (which might be insecure, such as traditional leaded lights), the installation of a secondary glazing system that is certificated to  PAS 24 2012 Enhanced security performance requirements for doorsets and windows in the UK. External doorsets and windows intended to offer a level of security suitable for dwellings and other buildings exposed to comparable risk will be your solution to this unfortunate dilemma.  (Formally BS 7950:1997 Specification for enhanced security performance of windows for domestic applications)   (See  Windows of enhanced security

Please note that BS 7950: 1997 is still quoted on some manufacturers' websites and sales literature.

However, enhanced security secondary glazing can also be used in place of bars and grilles, which are often seen on the outside or inside of very vulnerable windows in basement flats, for instance.  Potentially you could have PAS 24 primary windows and PAS 24 secondary glazed units behind, doubling up the security resistance of that vulnerable window.  The very same approach could be used to replace security roller shutters and so it seems to me that security rated secondary glazing has distinct advantages over other security products, including those listed below.

If you intend to use secondary glazing to improve your security then I must emphasise the importance of buying a product that has been tested and certificated to a recognised security standard.  Plenty of secondary glazing manufacturers will claim added security as a reason to choose their product, but you should be seeking independent third party approval to either PAS 24 or LPS 1175 to substantiate these claims. (See  Windows of enhanced security

Secondary glazing is also used in homes and other buildings where there are specific high level crime risks.  Strengthened frames with specialist glazing is used to protect people and property from bomb blast and ballistic objects.  In these cases, products are available that have been independently tested and certificated to the appropriate standards (See Library )   

Noise insulation

Secondary glazing is used a great deal to reduce the effects of noise pollution from traffic, trains, aircraft and other noise generated by leisure or industrial activity.  For the system to work efficiently installers seek to achieve a 100mm gap between the secondary glazing unit and the exiting window and the new window frame must be accurately formed to prevent noise leakage around the frame edges. 

Thermal insulation

A secondary glazing unit can improve the thermal efficiency of a window by more than 60% and bring your home in line with  Part L of the Building regulations .  This is another important reason to consider secondary glazing for homes where you cannot replace the primary widows.

Other benefits

Other benefits include, draught proofing and reduced dust penetration from outside and fade protection provided by the use of laminated glass, which blocks 99% of harmful UV light.

Further, important information on the uses of secondary glazing provided by Selectaglaze, the UK’s leading designer, manufacturer and installer of secondary glazing systems, founded in 1966 and a Royal Warrant Holder since 2004

Windows can be a very vulnerable part of a building, often seen as “soft targets” by vandals, criminals and terrorists alike, impacting on people’s safety and the protection of property.

The UK has a vast array of prominent and iconic buildings, particularly in city centres; with a multitude of uses including hotels, government, museums, offices, universities, clubs and, of course, residential, attracting people in large numbers to live, work, study and socialise.  

Electronic security will warn but not resist so physical security measures are an important part of any plan for protection and glass is easily broken by an intruder prepared to use force and offers little resistance to attack.  It will also be shattered by a bomb exploding more than 100M away and flying shards will maim and kill.

A solution is found with Selectaglaze’s secure secondary glazing systems where a fully separate window is fitted behind an existing window (room-side) using robust frames, secure locks and strengthened glass. These units can be hinged, sliding or fixed and are subjected to rigorous testing before certification.

The well-respected ‘Police Preferred Specification’ under the Secured by Design initiative requires frames to be tested to PAS 24. This test replicates an attempt to force the window or to remove the glass but does not include glass breakage. If resistance to breakage is important, an anti-bandit glass such as 11.5mm laminate should be considered.

Some buildings will need higher levels of protection due to function or occupancy. In these cases both the frame and glass must resist determined attack and products should be rigorously tested against a standard such as LPS 1175 from the Loss Prevention Certification Board. This offers a number of security ratings based on the tools used and the time available. Currently secondary windows are available to level 3 which replicates 5 minutes of continuous attack over a 20 minute period using tools such as a claw hammer, small axe, battery drill and long crow bar. This is a very severe test and one that only a small number of bar sets or grilles will resist. Secure secondary glazing provides the protection discreetly with minimal visual intrusion.

Secondary window frames and locks can be designed to absorb the significant pressures arising from a bomb blast and laminated glass with its integral sheet of plastic (pvb) material will stretch and hold the glass together safely.

Protection levels will depend on the risks to the building and potential distance from a bomb. Relatively slim sections glazed with 6.8mm laminate glass will survive at 45 metres from a typical vehicle bomb but heavier frames and glass are needed as the distance shortens. High profile buildings may require protection at 25M and sometimes at 15M.

Selectaglaze’s frames are designed to fit discretely and sympathetically in contemporary or period buildings. Listed building consents are usually granted.  Added benefits include significant levels of sound insulation, which is highly desirable in noisy locations and enhanced thermal insulation that will improve a building’s energy performance, thus saving on fuel costs.

Selectaglaze is the recipient of  the 2013 Security Industry E-Magazine’s “Blast Mitigation Product  Provider of the Year Award”, which: “Reflects the high standard provided by the company’s bespoke range of secondary glazing systems and the service it provides to clients across a broad customer base.” On receiving this Award Selectaglaze’s Chairman, Meredith Childerstone commented: “It is very pleasing to receive sector recognition in this way. We pride ourselves in bringing modern standards to established buildings whilst improving the security of the original structure and maintaining a sympathetic approach to aesthetic qualities. City centres are renowned for staying constantly busy around the clock. Therefore it is imperative for businesses and residential properties alike to provide a safe, quiet and comfortable environment for the occupants. And, of course, our secondary glazing systems bring additional advantages such as enhanced energy performance and reduced ingress of dirt and dust.”

Although London and the south of England is the company’s predominant marketplace, Selectaglaze and it’s approved regional agents, have embarked on highly successful projects all over the UK. Selectaglaze’s products have been well received and used extensively by Government, Police and the Services to assist in the protection of people and property.

Selectaglaze has recently updated its Security guidance literature, entitled “Protecting your Environment”. The literature will be of interest to architects, building surveyors, security consultants and contractors dealing with a range of projects including: Airports, Banks, Computer Rooms, Control Rooms, Embassies, Government Buildings, Private Homes, Hospital, Laboratories, Museums, Schools, Transport Links, Telecommunications and Utilities. Selectaglaze’s literature is free upon request from the Marketing Department.

For further information about this award winning company, please call Selectaglaze on 01727 837271; email: or visit the company’s comprehensive website at