The most creaking, cracking floorboards ever? What's wrong?

Have you had a go yet Snow?

Just to spur you on, I've made a start and this is how I got on:
I have ring shank nails as mentioned above. My word the force required to remove the few that had lifted was tremendous.

I was very lucky as the boards were mostly marked where the pipes were run, there was one area not marked but I could easily trace the pipes with my thermal imaging camera.

The joints on the ends of the boards where they do not land on joists, have not been glued or supported with noggins. These are still squeaking.

Once I had rammed a load of screws in, the floor was much more solid, however certain areas were now squeaking even more!

The squeaking was along the stud walls, so I attacked the bottom 1' of the wall to remove the plasterboard and skirting, and the source of the squeaking was obvious. 4 rusty 5" nails had been banged in to fix the bottom of the stud wall to the floor. These were easy to remove as their heads were up by around 10mm. With these removed there was now silence, it was amazing!

I couldn't leave the wall swinging about, and I couldn't screw it down as it then pulled off the bottom plate of the wall, and the nails going into the end of the uprights squeaked then. So I forced the bottom plate back on with a lifting bar and rammed some hard wood packers underneath. The bottom plate was then screwed down through the packers, the chipboard and into the joists. Wall not moving and no more squeaks! I also angle screwed the ends of the uprights into the bottom plate.

However the bathroom floor is wrecked and needs replacing, the unsupported joints are still squeaking, as are the other 3 stud walls I haven't attacked. The chipboard is sort of soft and spongy in some areas too, like the glue holding the wood particles together has given up. I also need to install a ventilation duct that was forgotten when the house was built, they put the fan in, and fitted a vent grill, but didn't join the 2! There is pipework that needs altering as it had been brought up in the wrong place in some locations too, so I am likely going to lift the whole lot up and replace it. I don't want to leave it and regret not doing it later. The ground floor is just as bad!

But right now I can walk around the rooms I use the most with only minor squeaks which has reduced my stress levels a bit!

Hopefully your floor is a bit easier to sort...

Hi freddo, not tackled this yet.

Not sure what you mean by bottom plate? Could you elaborate? Those pictures are helpful for understanding what you mean in general, and I wouldn't be surprised if I found something similar going on.

Interesting about the vent too. I have noticed that there is the beginings of mold in the top corner of that same room, very odd I thought. No damp elsewhere in the house, as a year ago I replaced the powerless extractor fan in the en-suite with one that actually removes air and moisture from the shower. When I did that I found the extractor was not attached to the ducting in the loft so I attached it and all has been good in that en-suite since. But guess where that ducting comes out? I checked today and it does not exit through an outside vent (as the one in the main bathroom does) but rather, it just exits into the outer loft space - right in the corner where I am getting mold in the bedroom. The new fan has obviously meant that water vapour is getting extracted into this space, and presumable causing damp there. I'm not really sure how to resolve this as there is no outside vent there that I can attach the ducting to.

Given these two situations, I think I am going to try and get them resolved under the buildmark guarentee thing. No idea if I will have any luck with that.