On 2016-05-15, Tim Lamb wrote:

In message , Adam Funk
writes
I've had to do some exploratory & other surgery in the kitchen ceiling
(also bathroom floor) as a result of a loose connection in an old
junction box (kitchen & bathroom lights went off sometimes but came
back on if you stepped on the right area on the bathroom floor).
That's all fine now (Wago box; new ceiling light; big mess cleaned
up), but I wonder about the weird situation I found in the
ceiling/floor.

= bathroom floor
- kitchen ceiling
X joist


================================
XX XX
XX XX XX XX
XX XX XX XX
XX XX
--------------------------------

That's a cross-section. There seem to be two sets of joists: one set
has a gap above & the (lath & plaster) ceiling attached below; the
other has a gap below & the floorboards attached above. I've only
worked in the middle, so I don't know how the ends of the joists are
attached to the walls.

Any explanation for this weird situation?

Your diagram does not display well with my reader.

It's meant for monospace. I forgot to clarify in the text that there
is a gap of 25 to 30 mm between each low joist & the adjacent high
joist --- it's not *too* difficult to snake lighting cable under, up,
& over them, between holes in the kitchen ceiling on opposite sides of
a joist pair.


We had a similar situation where dormers had been added to a bungalow.
The existing loft floor joists were probably 7"x2" and the new floor
joists 9"x2".

It would have been much better if they had bolted the joist pairs
together as loading the new floor tended to ping the plasterboard nails
off the downstairs ceiling.

Also done where there is a load such as a cold water header tank.

AFAICT, the ground floor kitchen & 1st floor bathroom were built at
the same time as one offshot (on a mid-terrace).

I'm reluctant to go back & take more measurements because I'd have to
clean the dust out of the kitchen again!