Garry Nutter wrote:

Thanks everyone, for the help. John your site is a aladins cave of
information. Could i ask how do you arrive at the position of the Knee
Wall.

The wall is a load bearing wall and takes the place of the purlin that
was removed from the front of the roof slope. So its position is chosen
to be roughly mid span of the front rafters and not that far from the
original purlin location. In reality it could go a few feet either way -
its location is not that critical.

As i only have 8 rafters i was going to sister a furthur 150*50 to each
rafter, and tie them in at the top, to make a triangle. Could i get
away with 150*50, coudnt find any information on the web of the correct
size for this.

To answer questions like this you need to do (or get done) some design
calculations based on the anticipated loadings. In many respects you
would probably find it easier to build a new floor without connecting it
in any way to the existing trusses. You could also take the same
approach to supporting the roof, or you could look at ways of reusing
some of original truss components. The difficult thing with the trusses
is that they are only structurally strong in their complete form. They
don't have much rigidity the moment you chop bits out of them (although
they are probably strong enough to hold up the facias and soffits by
themselves ;-)

150*50 is going to be well undersized for a floor at that span. It is
probably more heavy than required for rafters though. Having said that
it does depend on the type of roof and its pitch, and the spacings of
the rafters. Note there is no need to maintain the same spacing as the
trusses - you could insert more rafters if you wanted.

--
Cheers,

John.

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