UICollectionView adds top margin

The issue may be in collection view's content insets. Try to add self.automaticallyAdjustsScrollViewInsets = NO; into view controller's viewDidLoad method.

You can set this in the storyboard too.

Make sure you've selected the ViewController, and then untick "Adjust Scroll View Insets".

I haven't tested what this IB/Storyboard method does on iOS6 though. With the code method you need to check that the VC responds to the method:

if ([self respondsToSelector:@selector(setAutomaticallyAdjustsScrollViewInsets:)]) {
self.automaticallyAdjustsScrollViewInsets = NO;
}