# What is secondary glazing?

Secondary glazing is an additional internal window frame installed on the inside of a single-glazed window to create a second layer of glazing. Installing secondary glazing creates a minimum air gap of 50mm between the new frame and the original window to improve thermal efficiency and reduce draughts inside without changing the window’s external appearance.

Read our [secondary glazing](https://nathanmccarter.co.uk/secondary-glazing-windows/) article where we cover more details.