Good evening. This is my first posting to this esteemed newsgroup.

I'm in the process of renovating a chalet-type bungalow, in the course
of which I need to fit some 7 x 2 floor joists(OK, they're 170 x 50,
but I prefer to think in one system at a time). Half of my first floor
has proper 7 x 2 joists; the other half, for some reason, only has 4 x
2 ceiling joists. Something to do with the history of the building,
which had rooms added upstairs after it was built. I hadn't noticed
this feature until I removed the chipboard floor, as the chappie had
battened over them with 3 x 2s to make the floor levels match.

Anyway, I digress. Half of my first floor is joisted with 4 x 2 at 400
(ish) mm centres. There is a ground floor brick internal wall dividing
the space, and the span from this to the wall plates on either side of
it is about 3.5 m.

When installing my 50 x 170s, is there any significant advantage in
running them alongside the existing 4 x 2s and bolting them to them,
rather than running them independently between the 4 x 2s, and bolting
them together where they meet over the brick internal wall? It might
seem a no-brainer, except that the joists and the rafters of the
sloping roof both come down to the wall plate, and don't always meet,
which would in any case prevent all the new joists from touching the
old ones.

So I'm thinking of simply running the new (7 x 2) joists in the middle
of the gaps between the old (4 x 2) joists, nailing or bolting the
ends of the 7 x 2s together where they meet over the brick internal
wall, and perhaps nogging them with 3 x 2 which I would then nail down
into the old 4 x 2s where the noggins crossed them. I should add that
the existing 4 x 2s have a tie-beam nailed above them, half way along
their span, on either side of the internal brick wall.

A long-winded way of asking a simple question, sorry. I've not done
this before and it is pushing the envelope of my DIY ;-) If anyojne
has any general comments or advice, I'd be pleasd to hear them.

Regards
Richard