Stiffen bouncy floor

[paulg1]

My new house has a recent extension which feels very bouncy on the first floor. There's some heavy oak furniture in the room and it doesn't "feel" very safe, although I acknowledge that it's probably unlikely that the floor will actually fail.

The span is just under 3.8m and the timber joists are 47x195mm with 400mm spacing (which I believe is in within regulations). As far as I can tell the joists have no noggins or anything along the span, but I've only lifted one bit of floorboard so I'm not 100% sure of that. I can't see any cracking in the ceiling beneath the room. I've attached a picture of the joists where they meet the wall

The subfloor is 18mm P5 chipboard which has been quite well screwed to the joists and the floor itself is a floating laminate floor. I have no love for laminate in a bedroom so I plan to carpet the room regardless (which should help with soundproofing anyway).

My real concern is that just carpeting it won't be enough to stop the bounce and maybe I should be doing something to stiffen the floor itself: The bounce is even more noticeable when walking across the subfloor on the part of the room where I've lifted the laminate. I'm not sure if this is normal though. Is there any objective measurement I can take?

Maybe I should look at sistering the joists or adding noggins between them? And maybe replacing the chipboard with plywood or even old-fashioned floor boards?

Other considerations:
- The floor has two partition walls built over the subfloor already (one to some eaves, one to an en-suite bathroom)
- The en-suite is tiled and the floor feels unsteady in there too.
- I don't want to just throw money away, but I'm happy to spend a bit of cash to get the floor I want.
- Half the room is spanned off an RSJ and half between brick walls. There's no difference in bounce between the two though so I don't think the RSJ is a factor.

Any comments or advice would be greatly appreciated.

 

[theprinceofdarkness]

The bounce could be due to the laminate under lay.
Frank

 

[paulg1]

I don't think that's it. I experience the bounce/shuddering even if walking directly on the chipboard.

 

[RonnyRaygun]

If grade C16 the joists might be struggling a bit. Noggins will help to spread the load between the joists and should help to reduce the bounce a bit

 

[JohnD]

I also find that 18mm ply feels more rigid and "flatter" than chipboard. Well screwed down, it forms a good platform. You can nog when you have ripped the chipboard up (it will be useful on November 5th).

I never learned to do herringbone strutting but it might be even better.

 

[paulg1]

Thanks all. Does undersized joists sound like a feasible cause given my joists and span then? Given that 47x195mm joists have a max recommended span of 4.04m, 3.8m seems bit close (http://www.home-extension.co.uk/tech2.html). The thing is: although I've read a lot about this, I don't have any practical experience of what a floor that close to the building regs limits would be expected to feel like.

I think I'll take up some more subfloor, check more thoroughly for noggins or braces, and price up what adding noggins and a plywood floor would cost.