In article ,
The Natural Philosopher wrote:
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?

No. It's a Victorian house. The original attic room had the wall studs
which formed triangulation between the joists and rafters. I wanted to
remove these walls


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 ;-)

Then you provide steel rafters at either end to take the load of the steel
purlins. Don't you ever watch Grand Designs? ;-)

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..

The name purlin is as old as the hills - long before roof trusses as we
know them today. On a simple structure where you don't want individual
joists tying the bottoms of rafters together - like say a small church -
the purlins are tied by joists at either end as well as the gable. And the
rafters mounted on a wall plate with the same arrangement.

--
*Experience is something you don't get until just after you need it.*

Dave Plowman London SW
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