Dave Plowman (News) wrote:

I would be more interested to see a superbeam calc for the purlin -
having to hold the roof up all on its own, once the stud wall under it
has been removed. [I may be wrong, but I suspect that the purlin is
currently supported all along its length by load-bearing walls which go
all the way down to ground level].


Wouldn't that be a bit unusual in the normal two rooms per floor house?

It is quite common to have a stay somewhere in the middle of the purlin
to brace it, however that function may be being satisfied by the wall
transferring the load to the floor of the loft (or more accurately a
beam spanning the width of the house under the floor).

It would be interesting to know what kind beam is under the wall marked
with "***1*****" on the diagram.

I had a similar problem when I did my loft, there were purlins on three
sides mid way along the span of the rafters. Two of these were going
since the pitched roof was also going (gable wall on one side, and
dormer on the rear). The front one however needed to be replaced with a
dwarf wall to support all the front rafters.

If you look:

http://www.internode.co.uk/loft/images/beams1.jpg

The original purlin can just be seen here (with the fluorescent light on
it). The stay runs obliquely down from roughly the middle of the purlin
to a the supporting wall in the middle of the house.

In cross section you had:

/\
/ \
/ \
/ \
/ \
/P\ /p\
/ \ / \
/ \ / \
/ \ / \
## ## ##

Where "p" indicates the purlin running into the axis of the page.

The replacement was (with d indicating the dwarf wall):

/\________________
/ # #
/ # #
/ # #
/ # #
/ # # #
/ # # #
/ # # #\
/ #_____________#_________#__\
## # ## ##
d


See the first piccie after the "Finishing the Front" section:

http://www.internode.co.uk/loft/superstructure.htm



--
Cheers,

John.

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