How good is Slimlite double glazing for sash windows?

In this video SuperHomer Susan Venner talks about the options she considered for refurbishing her Victorian sash windows and reviews the Slimlite double glazing option she preferred.

Initially, three options were considered for the existing sash windows:

  • replace with new timber double or triple glazed windows
  • replace with new double glazed box sashes
  • keep existing sash windows and add secondary glazing

In the end, Susan went for a fourth option:

  • reglaze the existing sash windows with a thin Slimlite double glazed unit

The prime motivator for going with this fourth option was to avoid trashing the existing sashes which were in quite good condition.

Slimlite consists of two layers of 4mm glass with a 3mm cavity which is filled with krypton and xenon.

Fitting Slimlite involved taking out the single glazing and routing out 7mm more of the reveal into which the units could then be fitted.

The weights had to be increased in the box sashes. This was done by joiners. The process of refitting 9 windows took two joiners about 4 days. Susan also draught stripped the windows.

Using Slimlite improved the U value of the windows from about U 5.1 to U 1.9. The cost all-in worked out around £200 per meter squared including labour. For each sash window this meant a spend of between £300 – £400 which compares favourably with replacement sash windows which would have cost between £800 – £900 each.

Susan recommends using Slimlite double glazing if your existing sash windows have a deep enough frame – something you would have to check with the joiner and glass manufacturer. Using Slimlite means:

  • you can retain the existing sashes
  • the work is relatively straightforward
  • you don’t have to remove the whole window

Susan’s home has undergone extensive eco renovation and also includes the use of cork solid wall insulation. It is one of the homes in the SuperHomes network of older homes that have been renovated by their owners to reduce carbon emissions by at least 60%. Most SuperHomes host public open days in September. For more, visit Susan’s home.

Also see:
Sash window replacement
Secondary glazing for windows like mine
Energy efficient windows

eco renovation - talk to homeowners