i heard an excellent story this morning on the public radio program called living on earth. i definitely suggest you check out this show if you don't know it. this one was about a master thatcher named colin mcghee and the work he does here in the united stated building thatched roofs. the images above are from buildings he's worked on all over the u.s. here's his website: mcghee & company roof thatchers.
thatch functions as both shingle and underlayment
thatched roofs appear on every continent except antarctica
the top inch or so of the thatch is the only part that ever feels the effects of the elements
when a thatch roof needs to be repaired the new layer is placed right on top of the old
and old repaired roof can be up to 4 feet thick