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Conservation Joinery for Listed Buildings 

Thin double Glazing

The renovation of listed buildings comes under the direction of the local planning authority. Their decisions regarding updating original features centre on the need to maintain the original character and appearance of these historic buildings. This often leads to a requirement for like-for-like replacement of the windows and doors. While this does maintain the look of the building, it also constrains the manufacturer to bygone products which offer low levels of energy efficiency.

For example; our standard 24mm double glazed unit featuring soft-coat technology, a 16mm Argon-filled cavity, and a low “E” coating, will offer a centre-pane U-value of 1.1wm2k. A 4mm piece of single glazing will offer a centre-pane U-value of 4.5wm2k. In short, based on centre pane U-values, the double glazing is over 4 times more efficient than the single glazing.

If you do not understand the relevance of U-values, then try our blog posting, “The Mystery of U-Values”. This will open a new window or tab and not close the current page.

Why Can’t I Use Standard Double Glazing?

Standard double glazing is made up of two sheets of glass, separated by a cavity of between 12mm and 18mm. When this unit is viewed in application it will give two reflections; one from the outside pane and a second from the inside pane. This is deemed to be unacceptable, as it changes the appearance and character of the building. Also, the extra thickness of the double glazed unit, can require changes to the sections of the window and prevent the manufacturer from reaching the like-for-like appearance.

The Solution: Thin Double Glazed Units

Thin double glazed units are constructed with narrower cavities, replicating the look of single glazing on original timber windows with improved efficiency.

These units provide U-values in a range from 1.9wm2k to 1.2wm2k, dependent on the thickness of the cavity and the gas used to fill the cavity; this offers a level of thermal and sound insulation close to that of double glazing, without compromising the character, charm or value of their property. The reduced cavity means that the double reflection effect is reduced to the point of being almost unnoticeable and that the section changes are lessened or unnecessary.

As such, we have now had our windows featuring these units approved in a variety of local planning authorities across Derbyshire and we have carried out many successful installations.

If you would like to talk to somebody about planning regulations and how ultra-thin double glazed units may be able to help you meet a compromise of appearance and efficiency, then call us today.

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