Can Listed Buildings Be Double Glazed?

In this article we look at double glazing in Listed Buildings

Buildings are given listed status by the local authority due to their significance in the local built environment, they form part of the history of the town or city where they are located and often have special architectural features that need to be protected from unsympathetic development.

Living in a listed property comes with it’s own challenges, not least of which is improving comfort , reducing heating bills and our carbon footprint in a property that was never designed with a great focus on heat insulation.

Therefore the first port of call must always be to gain approval from the local Conservation Officer to any change in the building that may be affected by it’s listed status.

Existing windows are a natural focal point for heat loss and one of the most common requests is to double glaze the existing single glazed windows. Assuming that an efficient draught reduction system has been fitted and secondary glazing (which usually does not require listed building consent) has been ruled out due to internal features such as shutters, then application for double glazing may be appropriate.

Existing period timber windows have very small glazing rebates. Re-working the rebates to make them deeper can often be difficult and will result in a change to the existing timber mouldings. So trying to squeeze a standard slim double glazed unit into the rebates raises problems. Often they use modern flat glass which gives an unsightly double reflection, and there are many examples where the black edge spacer is clearly visible around each pane. Also the amount of face putty can be so small as to be in-effective for water run-off. It’s easy to understand why Conservation Officers are concerned about the visual impact on listed buildings.

One possible solution is the use of the new generation of vacuum glazed insulating units such as Pilkington Spacia TM.  At only 6.5mm thin, none of the normal edge spacer problems and no double reflection it can often replace single glazing and be barely noticeable yet improve the thermal efficiency by a factor of 5.