Rendered property is only for enabling or disabling component value
that takes boolean which is by default true
As you said you are adding one row by add button.
as one you submit new record , you add into old collection I guess
Just assure that jsf property of that collection should mapped with business bean not with pagebean as Business Bean Scope is at session level & Page bean
Scope is at Request level
So ,Problem is with page scope not with rendered...
