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Fax: 0208 867 2767


Tel: 0800 043 1054
Fax: 0208 867 2767

Top 10 reasons for choosing slimline double-glazing over standard double-glazing for conservation, listed and period properties

1. Authentic heritage look for period properties

Slimline double glazing perfectly replicate the appearance and features of single glazing on original timber windows for period, conservation and listed properties. This allows homeowners to gain all the thermal and sound benefits of double glazing without compromising the character, charm or value of their property. From the exterior and the interior (unless you look very closely), you can’t tell that the windows have double-glazing fitted. With standard double glazing it is immediately apparent that the glass has been changed which is detrimental to the character of the property as well as its value.

2. Thermal efficiency to beat standard double-glazing

The thermal efficiency benefits of slimline double-glazing can now be even better than standard double-glazing, achieving U-values (the term used to measure thermal efficiency) of as low as 1.2 on a 6mm gas-filled cavity, depending on the type of gas fill used. The reduction of heat loss through the glass is up to 77 per cent as when compared against single glazing and it is possible for slimline units on some windows to achieve Part L building regulations for thermal efficiency.

3. No double reflection

Slimline double-glazed units do not produce the unnatural ‘double reflection’ or ‘distorted reflection’ that is sometimes seen when you use standard double glazing.

4. Authentic variable reflection

For period windows, each slimline unit is fitted on a bedding putty compound in the same way the windows would have originally been made – which gives each pane a slightly different reflective angle of light in keeping with the original look and character of any period property façade. With standard double glazing, the only option is to have one large glass unit with timber glazing bars applied (or stuck on) to the surface of the glass, giving the same reflective angle from each and every pane, which can look modern and unnatural.

5. Putty line beadsCasement window being hand-puttied

Slimline units are glazed into position using a 9mm x 9mm putty line glazing bead to match the original design and proportions of the original putty bead used for single glazing in period properties, as opposed to the larger glazing beads required by standard double glazing that change the proportions and section sizes of the windows.

6. Planning approval and support

Slimline double-glazing is now gaining favour and acceptance over standard double glazing from architects, contractors and planning authorities around the country for replacing single glazing in period, listed and conservation/heritage properties. At Timbalite our slimline double glazed units have been approved by planning authorities throughout the country for listed, conservation and period properties.

7. Reduced cost

The cost differential between slimline double-glazing and standard double-glazing has reduced greatly over recent years.

8. Wide choice and availability

The availability of slimline double-glazing is now much wider and joiners are more used to fitting it. There are a wide variety of glass types and finishes to choose from, such as laminated glass and acoustic glass for improved security and sound insulation, and finishes including modern satin through to more traditional fleur finishes to match original details. If your joiner hasn’t used slimline double-glazing glass before, he or she can ask advice about fitting it from glass suppliers such as Timbalite.

9. Easy replacement

Replacing the individual panes of slimline double-glazing is easy should the need ever arise to replace a cracked or damaged pane. As standard double-glazed windows can only be made with a single large glazing unit, if the window breaks then the glass to the whole window will need to be replaced – requiring the services of both a glazier to replace the glass and a skilled joiner to replicate and replace the timber beads to achieve a satisfactory replacement. With slimline double-glazing, as with single glazing, you would just need to replace the individual broken pane, making the job a lot simpler. Timbalite slimline double-glazed units are characterised by their low failure rate, so are very unlikely to need to be replaced as a result of unit failure.

10. Complete solution

Slimline double-glazing is suitable for many types of doors and windows, including sash windows, box sash windows, casement windows, sliding and bi-fold doors. They can be fitted into new joinery elements, and unlike standard double-glazed units, can often be retrofitted into existing original windows.

If you have any questions or would like further information on our Timbalite slimline double glazed units, please email us at or call 0208 893 4420.


  1. southern langsat on November 13, 2017 at 12:33 am

    Aρpгeciatе this post. Let me try іt out.

  2. Amanda Drew on December 14, 2017 at 8:24 pm

    That’s cool that when you have double glazed windows, you only need to replace one pane instead of the whole window if it gets damaged. My current windows are rather old, and they’re letting in drafts and letting out air. It seems like it would be good for me to find some double glazed ones to replace them with.

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