Hi jkoella, Gordon & Roger,
I think that Jkoella's original question pertained to building a garden shed and not building a castle roof - the spans being quite different.
The language symantics are I am sure well meant but if I can make so bold as to suggest that if you adopt the use of the words - "cross frame" then the problem goes away.
Very few hammer beamed roofs in olde England are identical and therefore it would be inadviseable to generalise on what does or does not comprise a hammer beam roof type. There can be a degree of gender identity crises with some roofs where one is not quite sure whether a hammer beam roof is just that or whether it is more akin to an arch braced roof or maybe related to being an upper cruck or from time to time scissor bracing is introduced for good measure. The one thing that they all have in common is an interrupted tie beam and for that reason this device has been employed to span quite large distances using shorter lengths of timber.
Gordon is correct to highlight that where tie beams are interrupted then quite large deflections can develop but in a garden shed this is probably not worth worrying about.
Ken Hume P.Eng.
