Yes is 0 by default. You should set the content size of your scrollview by summing all the views height and the spaces between them, example:
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 320, 60)];
scrollView.backgroundColor = [UIColor blueColor];
[self.view addSubview:scrollView];
NSUInteger spaceBetweenLabels = 10;
UILabel *firstLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 0, 300, 40)];
firstLabel.text = @"first label text";
UILabel *secondLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, spaceBetweenLabels + firstLabel.frame.size.height, 300, 40)];
secondLabel.text = @"second label text";
[scrollView addSubview:firstLabel];
[scrollView addSubview:secondLabel];
CGSize fullContentSize = CGSizeMake(300, firstLabel.frame.size.height + secondLabel.frame.size.height + spaceBetweenLabels);
[scrollView setContentSize:fullContentSize];
Of course if your scroll view height is higher than the content size height it won't scroll because everything is on the screen.