Bounce in upstairs floor

[cabuckley]

We're adding a large open plan extension with a couple of bedrooms on the floor above it - posi trusses went in 16 weeks ago with yellow tongue on the floor upstairs. The first floor has now developed a significant bounce which wasn't there before when we last inspected 12 weeks ago. Can anyone suggest why? Could it be that the yellow tongue has absorbed too much rain and lifted slightly off the posi trusses? Will this correct itself when the yellow tongue dries out? If not what could have caused the problem to develop and how can the bounce be fixed?

[Uncle Bob]

In this 12 week window, were any walls removed downstairs?

[cabuckley]

No, no changes at all except the upstairs trusses were put up.

[Bloss]

Something has moved to make that change. It might be due to the weight of the trusses coming onto the outer wall, but shouldn't be! In any case unless you are DIYing this is problem to raise with your builder and sooner than later. I am assuming you can still get access underneath - or has the ceiling been put up? If it were me I'd be wanting to be able to see what has happened - and I would take down the plaster - or at least a section so I could get access and find out what has happened.

[cabuckley]

Spoke to the builder on Friday (the first day we noticed the problem). He's scratching his head too and said he will ask the engineer and will get back to us. The ceiling isn't up yet, still at frame stage so we can see the positruss with the yellow tongue sitting on top of them when we stand underneath and today we noticed a gap of 2-4mm in the areas most affected by bounce. Could this explain it. Why has the gap occurred? Could the yellow tongue have absorbed too much rain and swelled/lifted. The yellow tongue is all nailed down but our builder is suggesting we should screw it down instead of nail to correct the problem. Will this help? Should we just bite the bullet and replace all the yellow tongue then screw? We don't want to go through this expense if this isn't the cause of the problem.

[Bloss]

Spoke to the builder on Friday (the first day we noticed the problem). He's scratching his head too and said he will ask the engineer and will get back to us. The ceiling isn't up yet, still at frame stage so we can see the positruss with the yellow tongue sitting on top of them when we stand underneath and today we noticed a gap of 2-4mm in the areas most affected by bounce. Could this explain it. Why has the gap occurred? Could the yellow tongue have absorbed too much rain and swelled/lifted. The yellow tongue is all nailed down but our builder is suggesting we should screw it down instead of nail to correct the problem. Will this help? Should we just bite the bullet and replace all the yellow tongue then screw? We don't want to go through this expense if this isn't the cause of the problem.

Have a look at the thread on a faulty batch of yellow tongue - you might have the same. http://www.renovateforum.com/f203/yellow-tongue-flooring-drama-103932/ The bounce is due to the gap and it's your builder's problem - and should not be an expense for you! Screwing might fix it but you should get the supplier and the manufacturer of the flooring involved IMO.

[cabuckley]

Thanks; the link to the thread was very interesting; maybe the yellow tongue could be faulty, is one possibility. We'll talk to the builder tomorrow and see what he thinks. We'll post our progress and outcomes to keep everyone following this thread in the loop.

[cabuckley]

This is the response from the engineer...
"I went past site yesterday, and yes it is a little bouncy but the stiffness will increase when the walls are plastered and the ceiling battens and plaster are installed to the underside of the joists, floor finish installed and also any furniture will further dampen the floor

Also, I noticed that the strong backs were not fixed at the ends and in one room we would require an additional strong back
These strong backs should be installed in accordance with the posi strut guidelines as they will significantly reduce dampen vibrations".

The problem is the strong backs were cut into, to pass a support beam running through them and at right angles to them :C

[Bloss]

This is the response from the engineer...
"I went past site yesterday, and yes it is a little bouncy but the stiffness will increase when the walls are plastered and the ceiling battens and plaster are installed to the underside of the joists, floor finish installed and also any furniture will further dampen the floor

Also, I noticed that the strong backs were not fixed at the ends and in one room we would require an additional strong back
These strong backs should be installed in accordance with the posi strut guidelines as they will significantly reduce dampen vibrations".

The problem is the strong backs were cut into, to pass a support beam running through them and at right angles to them :C

Your builder needs to follow the posi-strut guidelines, but I would be concerned about the underlined advice above. It is true, but a motherhood really - any structure will be stiffer overall with all components finally in place and fixed as per spec - but that's a relative thing not related to discernible existing problems with a sub-floor structure during construction.

IE: that applies only if there are no gaps between the flooring and the sub-floor, before any of those items are added! There might well be an improvement, but I have never had a bouncy floor that was fixed without ensuring full load contact between the primary sub-floor components prior to the addition of surface materials.

The bounce should be brought to within 'normal' expectations before any cladding - especially underside cladding - as once cladded any work if the problem remains or recurs requires removal of that cladding!

So - get the strutting brought up to spec and all gaps closed before relying on subsequent work (battens, cladding etc) to improve the situation.

[cabuckley]

Many thanks for your advice :); will do.