DaVinci Roofscapes steep slope roofing tiles are designed with an engineered rib structure to make them strong, and assure that they stay flat. This rib structure does a very good job keeping the DaVinci composite shake and slate tiles flat. In fact the rib structure prevents the tiles from curling down to follow the contours and bumps on uneven roof deck. This is why it is always important to make sure the deck is flat and clean. A small bump in the decking can cause the butt of the tiles to rise farther than the original bump. In the following picture you can see that a 1/8" shim can cause the butt of the tile to rise 1/4" or more.