Double glazing is frequently presented as a direct route to a higher NatHERS star rating. It can be an effective improvement, particularly where heat transfer through the windows is limiting the dwelling’s thermal performance. It is not, however, a guaranteed or identical solution for every project.

NatHERS does not assess the number of glass panes in isolation. The model uses the thermal properties of the complete window system, including the glass, frame, seals and other relevant components. Window size, location, orientation and shading also influence how that system performs within the dwelling.

This guide focuses specifically on when double glazing may improve the model, what the window performance values mean and which information should be coordinated with the assessor and supplier.

For the broader relationship between climate, orientation, shading, insulation and building form, see How to Design a 7 Star NatHERS Home.