What distinguishes a decorative screen from a privacy screen?
Well, a privacy screen can be decorative but a decorative screen may not necessarily give you privacy.
The main consideration is the screen density. Many councils will specify a minimum density of between 70%-80% as being a privacy screen.
Anything less than this must be described as purely decorative.
Take the 2 images below. The leaf pattern has a density of about 76% while the Moroccan pattern has a density of about 50%.
Both are decorative screens but only the leaf pattern, could be described as a privacy screen.