Grade II listed refurbishment project in Cobham

Conservation officers often request that listed or conservation properties be fitted with secondary glazing rather than having the original timber windows replaced.

This is because it is seen as a solution for thermal and acoustic insulation, without having to alter the original sash windows or casement windows in any way.

However there are high performance alternatives to secondary glazing which have been approved by Conservation officers, that don’t have the drawbacks of secondary glazing.

What is secondary glazing?

Secondary glazing is an additional single or double glazed window, usually aluminium, fitted behind the original existing window. This can be fitted in conjunction with repair works to the original window, and is often fitted when conservation officers have specified that windows can only be repaired.

Advantages of secondary glazing

  • Retains the original window
  • Cost effective
  • Provides thermal and acoustic insulation without altering the fabric of the original windows
  • Tends to have better acoustic insulation than double glazing but less thermally efficient

Disadvantages of secondary glazing

  • Unattractive – usually made of aluminium, and protrudes into a room
  • Creates an obvious double reflection
  • Creates condensation between the windows
  • More difficult to clean and open the original windows

High performance alternatives to secondary glazing

At Timbawood we offer a number of alternatives to secondary glazing. We have successfully fulfilled the strict planning criteria to replace or part replace windows and doors on listed and conservation properties in over 30 planning authorities throughout London and the Home Counties. 

Grade II listed sash windows - alternatives to secondary glazing

The range of solutions we offer include:

1. Repair and reglaze with specialist glazing

This solution is suitable when the windows and/ or doors are in good enough condition to be retained, and the planning authority will only accept repair or single glazed replacement windows. Windows are repaired, draught-proofed, and reglazed with laminated or acoustic single glazing. Our specialist laminated single glazing, ‘Timbawood Solo‘ can improve acoustic insulation (ie reduce unwanted noise) by up to 40% when compared to standard single glazing, and thermal insulation by 38%. It can also feature restoration glass or mouth blown cylinder glass on the outer face for the authentic uneven reflection of the original glass. Full perimeter draught proofing with compression seals (rather than brush seals) will also improve both acoustic insulation and thermal insulation. 

2. Replacement sashes/ casements to existing frames with slimline double glazing

Many planning authorities have accepted our bespoke replacement sashes/ casements with slimline double glazing because of their authentic heritage look. 
Heritage timber sash window
Each window is handmade in our London factory and includes slimline double glazing from just 11mm thick, that looks just like single glazing and reduces the problem of a double reflection. We use individual double glazed units which can include restoration glass on the outer face, and can be hand puttied as they would have originally been made. To compensate for the narrower cavity we use denser gas (Krypton or Xenon) to improve thermal efficiency.

This is a suitable option when windows are in poor condition and can’t be saved, but the frames can be. By replacing the moving parts only, more of the original architecture is retained, and the sashes/ casements can be single or slimline double glazed, depending on the requirements of the planning authority.

As well as being thermally efficient, slimline double glazed units can include acoustic glass to enhance acoustic insulation to the level of secondary glazing.

3. Full replacement windows with slimline double glazing

If the entire window and frame is beyond repair, we can fully replace heritage windows with sensitive, exact-match replacements. These sash windows and casement windows can include thermally efficient single or our slimline double glazing, depending on the requirements of the planning authority. 

As with part replacement, each window is handmade in our London factory to match every detail of the original window. Windows can be hand puttied and hand painted, with individual slimline double glazing from 11mm or single glazing.

If you are looking for alternatives to secondary glazing for your project, please get in touch to find out more about the various options available, and to arrange a free survey or quotation, or to visit our showroom.

As experts in bespoke timber windows and doors for period, conservation and listed properties, we manufacture and install timber casement windows, sash windows, French doors, Front doors, bifold doors and internal doors.