Most hard tennis courts are made up of a open textured macadam, normally laid between 30 to 50mm in depth, laid on top of 14mm stone allowing it to be a free draining surface. Therefore playable for most of the year.
Maintenance of this type of court is essential even on brand new courts. Moss is a major problem and should never be allowed to gain a foothold. The moss as it grow forces the macadam apart and when you come to clean it macadam comes out, in extreme cases I have seen courts completely ruined because of the simplest maintenance program.