Are there minimum weight requirements for exterior paving?

There are no minimum weight requirements, legislative controls or EU/British Standards relating to raised paving and its weight.

Some waterproof roofing systems, primarily the more old fashioned loose lay systems such as ballasted roofs, do require a minimum weight to be applied per m².

If this sort of system is being specified then you would need to check with the roofing system manufacturer regarding ballasting weights – but generally, the modern systems such as warm roofs, do not require ballasting as they are mechanically fixed or adhered.