Approved Document L, F and O FAQ’s

The Government has announced changes to three building regulations for new and existing homes to help the UK deliver net zero emissions by 2050. This comes in the form of three Approved Documents; L, F, and O.

We have compiled some frequently asked questions on the new regulations to help you better understand the new requirements and what effect these changes will have on your windows and doors.


Why are the new regulations being introduced?


What is the Future Homes Standard?


When do the new regulations come into force?


Document L

What is Approved Document L?


What does the changes to Document L mean for my windows and doors?


What are the new thermal regulations for my windows and doors under Document L?


What is an U-value and how is it calculated?


What is Window/Door Energy Ratings?


Document F

What is Approved Document F?


What do changes to Document F mean for my windows and doors?


Document O

What is Approved Document O?


How will Document O effect my windows and doors?