cracked purlin structural failure

Only one of the 4 purlins is showing signs of bowing (now cracked). In the roof space originally there were no struts
when i said strut i mean strut. The building is about 5.6 mtr wide, quite a span for a 9 x 3 with no struts.
a rafter length of around 4 mtr and a purlin half way up .. wheres the other positioned?
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the other purlin is located much closer to the eaves, I estimate about 18" above the current loft floor.
when i said strut i mean strut.
The problem for me is to understand what strut is as for me it is a generic term, but based on the sketch I attached I understand it is a timber support which is attached to a rafter directly under the purlin and runs at 90° to the rafter connecting to a floor/ceiling joist.

Its purpose would be to offer resistance to a purlin moving or deflecting toward the eaves is that correct ?
What kind of dimensions would this strut have for a 9x3 purlin ?
There would be two per purlin so eight in total or would only the upper purlin be strutted ?
In addition to struts the purlin/strut junction is braced to the opposing strut with a pitch to pitch "collar"
If one wanted to use the loft space as a livable space then the presence of struts and collars would reduce the useable space, how if at all could one provide the the suppport needed without these components ?
a purlin that low would be doing very little.
i would expect to see two struts each side at a minimum of 5x3. on the centre/top purlin.

Assuming the new floor joists are correctly sized and fitted then a timber ashlar wall would be fitted along with a suitable ridge beam
that would be designed by your SE
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wonder why it is there then, could it be to do with the fact it was I believe once end of terrace ?
The floor joists are 200x75 C24,
do you mean something like in the attached picture? in this picture I do not see any evidence of a purlin it seems that this line of vertical struts is doing the work of a purlin is that correct ? They appear to be bolted to the rafters.


  • ashlarwall.jpg
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