Secondary glazing
Secondary Glazing Where Original Windows Stay
Secondary glazing adds a separate glazed layer on the room side of an existing window. We fit secondary glazing where keeping the original windows is the right approach, considering the room, the opening arrangement and any restrictions on the property.
Keep the original window, add an inner layer
Secondary glazing is not the same as changing an existing sealed unit from double to triple glazing. It creates another glazed assembly inside the room, separate from the original window. That can be useful where the outside appearance or original material needs to stay.
The existing window still matters. Decayed timber, failed joints or a leak from outside should be addressed rather than hidden behind another pane. The assessment considers the original window and the space available for the inner layer, so the proposed installation has a sound starting point.
Period homes and protected details
In a period home, frame proportions, glazing bars and original joinery can be important parts of the building's character. An internal glazed layer may offer a way to improve the room while leaving the outer window in place, but the design should be considered from inside as well as outside.
Position the secondary frame with the existing sightlines in mind. An inner bar running across the middle of an original pane can be more noticeable than expected. Curtains, shutters and internal mouldings also affect the space available, so a measured survey matters more than choosing a generic size.
Secondary glazing for sash windows
A sash window needs access for its sliding sections, handles and any catches. The secondary assembly should allow the original window to be operated where required, while also providing a practical way to reach the glass for cleaning.
The inner opening arrangement should suit the size and use of the window. A layout that is convenient on a small ground-floor opening may be awkward on a tall upper-floor sash. Discuss how frequently you open the original window and how the secondary panels will be used, rather than considering only their closed appearance.
Comfort, noise and the whole room
An additional glazed layer can reduce air movement and heat transfer through the opening. The specification, gap and fit influence the result. Noise performance also depends on the arrangement and seals, so describe your priorities before selecting the glazing rather than expecting any extra pane to behave alike.
Moisture and ventilation still need attention. Secondary glazing does not remove the need for extraction or appropriate airflow, and condensation between layers can relate to how the two assemblies are sealed and ventilated. Existing damp or mould deserves its own assessment, not just a new internal screen.
Access, cleaning and escape
The secondary layer must work with everyday life in the room. Think about reaching catches, opening shutters, clearing the sill and cleaning both faces of the inner glass and the original window. An installation that cannot be maintained comfortably is less useful even if it looks neat when closed.
Where an opening contributes to emergency escape, any inner glazing must be considered alongside that requirement. Do not assume an added panel can block access to the original sash. The room's use and any safety obligations should be discussed before fixing the secondary arrangement.
Permissions and the scope of the quote
Internal secondary glazing may have a different planning position from external replacement, but listed status or other restrictions can still affect the work. Check the specific property with the local authority before ordering. Retaining the original window does not automatically mean no consent is needed.
Size, panel layout, glazing, fixings, internal finishes and access all influence the scope. We offer a free survey with a fixed written price and no-pressure quotations. Use the form below to explain which original windows you want to keep and what you would like to improve, so the inner glazing can be planned around them.
Questions
Common Questions
What is secondary glazing?
It is a separate glazed assembly fitted on the room side of an existing window. The original window remains in place. It differs from replacing the glass inside a frame with a new double- or triple-glazed sealed unit.
Does secondary glazing need planning permission?
The answer depends on the property and restrictions, especially listed status. Internal work can still require consent where protected features are involved. Check with the local authority before ordering rather than assuming that an internal installation is unrestricted.
Can secondary glazing be used with sash windows?
Yes, where the inner layout is suitable for the opening. Access to catches, cleaning, ventilation and any escape requirement should be considered so the original sash remains practical to use.