PLASTICS AS PROTECTION OF CULTURES IN THE MEDITERRANEAN REGIONS
Subsequently the high tunnels were joined together into larger units. For vegetables however, span-roof houses appeared to be more suitable, and again there is a marked trend towards the use of combined structures rather than separate houses.
Polyethylene is now the roofing material° most frequently used. It is replaced every year. An increasing number of trials are being made with PVC and photoselective films.