I thought there was a bug

[RGSSoftware]

I believe you should set the values in your - (void)setup method to nil, as these values seem to be optional.

 - (void)setup {
    [self registerClass:[FRGWaterfallDecorationReusableView class] forDecorationViewOfKind:FRGWaterfallLayouDecorationKind];
    self.headerHeight = 26.0f;
    self.itemWidth = 140.0f;
    self.topInset = 10.0f;
    self.bottomInset = 10.0f;
    self.stickyHeader = YES;
}

When I init like so, but didn’t set ivar.headerHeight the collectionView is not viewed correctly.

FRGWaterfallCollectionViewLayout *collectionViewLayout = [[FRGWaterfallCollectionViewLayout alloc] init];
    collectionViewLayout.delegate = self;

    collectionViewLayout.itemWidth = 156.0f;
    [self.cv setCollectionViewLayout:cvLayout];