There are two types of UPVC fascia.
This type of fascia is only 9mm thick and fits on top of the existing timber fascia it is a cost effective way of giving your property a new and look and means no more painting!!
This as the name says all the old timber fascia is removed and completely replace with 18mm thick UPVC fascia, it's more costly however if the old fascia is completely rotten then this is the way to go.