Double Glazed Sealed Units

CN Glass manufacture Double Glazed Units by hand to British Standards BS EN1279 Parts 2 & 3.

A skilled workforce in traditional glass and glazing techniques working with the most up to date machinery providing high quality hand finished products for our customers.

The annealed glass is cut for production on our Automatic cutting bench then passed through our toughening plant where required before then taking the journey through the unit assembly line and finally the units are sealed by hand. In addition to this we also have a totally hand assembled and finished unit assembly line for our Heritage glass units, intended for period properties and timber frames.

We believe a hand finished unit produces a superior quality unit because each glass unit is constantly being monitored as it goes through manufacture and we are proud to put a 5 year guarantee on all our supply only double and triple glazed units subject to the glazing of the units also being carried out to British Standards BS 6262.

We guarantee our units for 10 years when we also carry out the installation of them into new frames.

Currently we are producing an average of 500 units per day for delivery to our customers.

CN Glass manufacture Double Glazed Units

Toughened Glass
Glass Toughening Plant NOW ACTIVE

  • Glass Tougheners
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Double Glazed Sealed Units

Double Glazed Sealed Units are manufactured by us using either Aluminium Spacer Bar or Warm Edge Spacer Bar to provide the air gap between the two panes of glass.

Eco-Slim Heritage Double Glazed Units

Super Spacer is produced down to a minimum depth of 4mm allowing us to produce the VERY THIN Double Glazed Units suitable for glazing in conservation areas and listed buildings (subject to planning permission). It is important to note that sometimes you do have to use Krypton/Xenon when limited width is available. i.e.: in old buildings for example.

Listed Property Magazine - A Glaziers Point of View
More information on our Slim Heritage Double Glazed units can be found in the following article published by ‘The Listed Property Magazine’.


The thickness of a normal double glazed sealed unit can vary in size depending on the frame. Below is a list of the thicknesses available:

Overall Depth Glass x Spacer Bar x Glass
• 14mm (4-6-4)
• 16mm (4-8-4)
• 18mm (4-10-4)
• 20mm (4-12-4)
• 22mm (4-14-4)
• 24mm (4-16-4)
• 28mm (4-20-4)

A 20mm spacer is the widest available, so using 4mm glass the widest unit will be 28mm which is used as standard in all our PVCu and Aluminium windows and doors, with thinner units more commonly used in timber frames.

The thickness of our double glazed units can vary depending on the project requirements.

Please call our friendly team on 01295 263364 for help finding the right fit for your project.

Most of the older timber frames tend to accommadate 14mm or 16mm units, with the newer timber frames (complying with the building regulations part L) typically being 20mm – 24mm.

Most sealed units we make now have ‘Low E’ glass to meet current building regulations and are 20mm or thicker.

Glass is a good insulator but it would need to be very thick as a single pane in a window to have much effect.
So rather than have thick glass in your windows it is better to have two panes of glass with an air or gas space between them. The bigger the air space, the less heat is lost, up to an optimum of 20mm.
All well designed and well fitted double glazed units significantly reduce the intrusion of unwanted noise.
By specifying glasses whose thickness differ by at least 30%, resonance effects are suppressed and the acoustic benefits are, therefore, maximized.

What are the benefits of having Double Glazed Units?

  • Heat loss through single glazing will be at least halved with double glazed units
  • Draughts through windows caused by sinking cooled air will be less with double glazed units
  • Rooms will be warmer with double glazed units
  • Outside noise can be reduced with double glazed units
  • Double Glazing Condensation LeafletCondensation can be reduced with double glazed units
  • Increases the saleability of the property with double glazed units
  • Savings on fuel bills with double glazed units


About Condensation On Glass

Critical locations

Since 1992 there has been a requirement in the England & Wales Building Regulations for robust or protected glazing in certain critical locations. This means the glass must either break safely, resist impact or be protected from impact by permanent guarding. Where Doubled Glazed Units are provided both sheets of glass will need to conform if people are likely to come into contact with the glass from either side (e.g. patio doors).

All tempered (i.e. toughened) or laminated glass must (with minor exceptions) be marked in accordance with BS6206.

Homeowners are becoming increasingly aware about safety in their homes and visible etched markings on all panes is the only evidence of complying with British Standards BS6206.

The diagram below shows the dark shaded areas as those requiring safety glass.

Small panes of 6mm annealed glass are suitable in critical locations if the area of the single pane is no more than 0.5m2 and the width of each pane is no more than 250mm.

Legal Requirements for Safety Glass Locations