The ridge is the top of the roof and the style of thatching varies, depending on material local tradition or customer choice. listed thatch buildings require listed building consent to change from one ridge type to another.
A block ridge is aptly named as it is a block of thatch on top of the roof, usually about 4 inches thick. This may be straight cut or patterned (Ornamental).
A flush ridge may also be called a turnover, wrapover or buttup ridge. These ridges as described are flush with the main coatwork and are usually decorated with a spar pattern. These ridges are commonly associated with Longstraw roofs but may be applied to any roof if desired (exception being a listed properties with an existing block ridge which would require listed buildings consent for any change
Whilst most thatched roof coatwork is Straw or Waterreed the ridges are usually done in straw. This could be Wheat Rhe, Tricale straw. Heather, sedge and turf have also been used for ridging. In Europe they use clay tiles for ridging on top of thatch which gives a very different effect.