MC... if it's your incoming main supply, then Water Companies insist that the pipework is around 750mm deep as it enters the house. It then rises to the stopcock position.
For any runs after the main has reached the stopcock, then it's really up to you to protect from freezing and/or damage as you see fit. Boxed in and insulated would be fine.
One way is to leave the cover off the duct, and squirt expanding foam around the pipework. Carve off the excess, and fit the cover. Don't just rely on that foam pipe lagging stuff. It invariably has exposed joints and corners.