On 04/03/2018 10:46, Tony Bolger wrote:
Sorry for the late reply, had trouble logging on.

The property is link detached with gable each end, no party walls.
75mm x 50 mm rafters supported by 3 purlins each side, no
joist/ceiling hangers, no internal supporting walls.

Architect has specified the purlins to be removed and deeper rafters
to be installed, possibly 75mm x 150mm to be confirmed.

So the existing rafters are actually 75mm deep already? (you suggested
50mm in the earlier post)

The question was how to remove the purlins and fit new rafters
because the deeper rafters wont go past the purlins which are
approximately 200mm deep.

While you might be able to notch an extra 75mm out of a 200mm deep
purlin, you are probably not going to be able to get the new rafter in
behind three of them.

The architect says this can all be done from inside without stripping
off the existing roof covering, not long been felted and reslated.

I kind of assumed it would involve removing sections of the purlins
in stages, fitting the new rafters as I go.

It sounds like that is what you will need to do in this case.

I assume the purlins will be supported with acro props etc from the
ground floor, possibly fit some temporary bracing etc.

Is this a single storey place then?

I was interested in the two approaches of removing the purlins, start
at one gable and work across v start in the middle and work towards
the gable, of the two, I am leaning towards the start-in-middle
approach so loads remain fairly equal on each gable, but any
constructive advice is most welcome.

As long as you are supporting the cut ends, then the loads at the gable
ends will either remain the same or go down.

I will of course seek guidance from the architect and SE and may
employ others to do this part of the job but want to know your
thoughts on how its done.



--
Cheers,

John.

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