Strange joists in offshot bathroom floor/kitchen ceiling

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?
Thanks, Adam
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On 5/15/2016 9:12 PM, Adam Funk wrote:

I imagine the extra joists have been added at some time in order to adjust the level of the bathroom floor. You don't state the age of the property (other than that with L&P it's presumably well over 50 years old) but in my 1780's cottage movement in the 2x2 inch oak joists means some of my floorboard would be all over the place without packing.
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On 2016-05-15, newshound wrote:

I think the rest of the house is 1910s & the kitchen & bathroom were added at some point (well over 50 years ago). Next time I get a chance I'll see if I can "periscope" (torch + phone camera) to see what's happening at the ends of the joists.
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Your diagram does not display well with my reader.
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.
--
Tim Lamb

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On 2016-05-15, Tim Lamb wrote:

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.

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!
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On 15/05/2016 22:27, Adam Funk wrote:

Is it only the bathroom or all upstairs floors? If all, could it be to decouple the floors and ceilings to reduce noise transmission?
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On 2016-05-15, Steve Walker wrote:

It's only in the offshot (bathroom above kitchen). I don't think they worried about "advanced" things like noise through floors when it was built.
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On 16/05/16 10:39, Adam Funk wrote:

It looks pretty clear to me. Originally there was no bathroom,. just a kitchen with a ceiling and possibly a flat roof.
Then the bathroom was added, and the ceiling joists were not at the right height, and or inadequate. so a new set of joist were laid in to take the floor
>>>AFAICT, the ground floor kitchen & 1st floor bathroom were built at >>> the same time as one offshot (on a mid-terrace).
I would say the evidence is against that, personally. Or it could be that the builder at the time had ordered 6x3 timber, was under pressure, and realised he needed 7x3, to match the existing house, and said 'sod that, I'll use two sets of joists instead and 6x3 timber' or whatever.
BTW WTDF is an 'offshot' bathroom? One what isn't in video view?
--
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On 16/05/2016 15:04, The Natural Philosopher wrote:

What does the "Wheelchair Tennis Development Fund" have to do with it?
Mike
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On 17/05/16 09:22, Muddymike wrote:

I could tell you, but then I'd have to kill you.
--
No Apple devices were knowingly used in the preparation of this post.

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On 2016-05-16, The Natural Philosopher wrote:

Definitely. The masonry shows the kitchen & bathroom were built together.

That could be it!

It's an extension, narrower than the rest of the house, behind a terraced house.
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On 17/05/2016 10:40, Adam Funk wrote:

I thought it was quite a standard term? A couple of feet lower IME too.
--
Cheers, Rob

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On 2016-05-17, RJH wrote:

A bit lower, not a couple of feet in our case. It may be a regional term.
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On Sunday, 15 May 2016 21:15:05 UTC+1, Adam Funk wrote:

It is likely intended to reduce sound transmission between the rooms.
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