This old black & white is still one of the best images I’ve come across.  (pl. 15, Illustrated Glossary of Architecture 1966, Harris & Lever)

There is precisely one Rhenish helm among all of England’s historic buildings, atop the tower of the Church of Saint Mary in Sompting, Sussex.  Certainly, there must have been others, but this is the sole survivor.  The distinctive form: four gables with a hipped roof above; a definitive feature of churches in the Rhineland, dating from the Romanesque.  Cecil Hewett, in English Historic Carpentry (1980, Phillimore & Co. Ltd.), places the origin of Sompting’s tower ca.950-1050 CE ; more recent evidence indicates that the timbers are from the 14th century, when the church belonged to the Knights Hospitallers.  Another authority, Cartwright, claimed that the tower was originally 25 feet higher, but was lowered during a late-18th century restoration.  http://www.sussexparishchurches.org/content/view/45/33/ has a thorough description of the building and it’s history.

It’s just possible that they are all correct.  The form certainly existed as early as the 11th century, the 14th century timbers may have been replacements of originals, and there are taller versions of the Rhenish helm.  Hewett’s drawings of Sompting are mostly of the core structure, and I have attempted to create a model based on his drawings, basic geometric proportion, and a fair amount of conjecture.

This is what Hewett shows of the structure: the crosstrees, king post, wall posts, rafters, purlins and braces.

The core structure, showing joinery.  And just for a sense of scale, from the back cover of English Historic Carpentry, a photo of Cecil Hewett standing on the cross tree.

The study model.  Note how the lower rafters join the feet of the upper rafters.  All the rafters must be on the diagonal axis, so that the upper planes fair with the roof plane, and the lower rafter cannot set above the plane of the upper rafter.  This is substantially different from Hewett’s drawing, but the only way to effectively resolve the planes.  

This model is 16″ x 16″ x 40″, intended as  1/12 scale.  The materials are reclaimed Eastern white pine, ¾”x ¾”, ½”x ½” and ⅜”x ½”; scaled 8″x 8″, 6″x 6″ and 4″x 6″.  From the photo, it is obvious that the Sompting timbers are considerably larger.

“The architectural and structural concept of the Rhenish helm is extraordinary; but its execution in carpentry at Sompting is a work of such assurance and competence, achieved with such economy of means, that it both indicates the work of a master and suggests the previous existence of a tradition of framing such works.”  Cecil Hewett