Are your trickle vents big enough?
Last year, the new Building Regulations Part F came into force. These are the Regs that cover ventilation
and an important change has been made regarding passive or background methods of ventilation such as the use of trickle vents.
There’s a lot of detail in the Regulations but in short, it’s likely that to comply you will need larger trickle vents. You can read more
about the changes here Revised Building Regulations Part F: an end of transition and you can find full details of the updated standards on the GOV.UK website.