Harry, 

I would say it's good to have at least a couple of inches underneath. If you don't it can be hard to get attachments on.

On my Yakima, I have "tower extenders" which make the gutter towers tall enough to clear the roof in the middle.

On Oct 8, 2011, at 6:29 AM, Harry Hoffman <hhoffman@IP-SOLUTIONS.NET> wrote:

> Hi all,
> 
> Through a great deal if patience I finally found all of the components for my roof rack on Craigslist.
> 
> A question for those with Thule kits. Are the crossbars meant to come in contact with the roof? Or should they be elevated slightly?
> 
> Also, as a matter of note for others searching, the minimum length for the crossbars is 58". This is with the standard roof gutter feet.
> 
> Cheers,
> Harry