Black Knight Secondary Glazing
Black Knight Secondary Glazing

Secondary Window Basics

Why fit a secondary window?

Much of the UK's housing stock includes sash windows and timber casement windows which by their very nature are prone to draughts, heat loss and excessive traffic and aircraft noise.


To overcome these issues we recommend installing a secondary window behind your sash windows or casement windows.


As well as enjoying greatly reduced energy costs you will make the room draught-free allowing you to use the whole room in comfort.


If noise is a particular problem then fitting a secondary window with specialist acoustic glass will make sleepless nights a thing of the past.

Secondary window applications

If you live in a Listed building or your property is in a conservation area you are almost certainly restricted in what you can do to your existing windows.


To protect the heritage of our period properties, local Planning Departments have extensive responsibilities and powers to ensure that inappropriate alterations are not undertaken by homeowners.

Fitting a secondary window in conservation areas is generally approved by Planning Officers without any need to make applications for planning permission. Whether you are looking to stop draughts, reduce heat loss or combat excessive noise, the discreet appearance of secondary glazing, together with excellent performance characteristics, make it the sensible choice for discerning clients.


If you live in a conservation area and want to install secondary glazing then English Heritage can help with guidance on conservation issues and we recommend that you consult with them at an early stage - click here for further guidance.

Our secondary windows and doors are designed so that once they are installed they are discreet and unobtrusive.

Secondary window thermal insulation

Our standard secondary glazing substantially improves thermal insulation and greatly reduces the heat loss associated with single glazed primary windows.


They can be made even more energy efficient by incorporating low emissivity glass that reflect heat back into the room or in exceptional circumstances some of our glazing designs can be fitted with sealed units for optimum performance.


Whatever option is included a Black Knight secondary window will reduce heating bills, stop draughts, save energy and improve the usability of the room.

Stopping noise using a secondary window

When specified for noise insulation the correct use of specialist laminated acoustic glass in secondary glazing will achieve greatly reduced levels of traffic, aircraft and general street noise reduction and soundproofing.

Secondary window condensation control

If condensation is a problem we recommend fitting a trickle ventilator. For more information please go to our condensation section.

Secondary window security


Our standard secondary window products improve security but for high-risk situations we can upgrade to include laminated security glass and additional multi point locks.