Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
Sorry TNP but I don't buy that argument. Purlins are often very
substantial pieces of timber and with a heavy roof they need to be. Very
few roofs have a pitch greater than 45 degrees so if the load is
resolved into rightangle components only half or less is being
transmitted directly down the rafter.
So where else does it go?
Unless your purlins are actually PROPPED all the weight of the roof is
transmitted via the rafter ends. There *is* no other point of support.
Think you need to look at applied mechanics...

Er. no. Thats what my masters is in.

It seems that the 'purlins' in this case ARE propped - at the gable ends.

And the roof is not a trussed roof at all.

Of course not. In my case - a loft conversion - the whole reason was to
get rid of any intruding bracing.

Did you have W bracing?


And the way you do this in essence is to
add a steel purlin from gable to gable for each roof span.


Assuming you HAVE gables at all ;-)

If you're talking about roof trusses then all a horizontal beam does is
tie them together - but then it's not really a purlin.

Well in fact the definitions I found rather suggest that that is in fact
exactly what a purlin IS. what you describe is something else entirely..