Bouncy floor - Can I use existing ceiling RSJ ?

[mike42]

Hello All

I'm replacing the floor in a room above the garage and right now the joists are now exposed from above. Joists are 195x47 at 400mm spacings. It was installed in the late 80s early 90s.

The span is around 5.3M which would appear to well exceed what is permitted. There is no sag but if I put my weight on one joist and apply my weight on and off there is quite a bit of bounce.

What I don't understand is that there is an existing rsj running under the centre of the joists. The ceiling joists are small 4x2s and they appear to be resting on it but the big floor joists hover over it by about 3mm. I'm surprised a few sheets of plasterboard need a big steel.

I was thinking of cutting some 2-3mm wood packers and jamming them inbetween the centre of the floor joists and the rsj just to take some of the bounce out of the floor. Is that a good or stupid idea and is the huge rsj really just there to take the weight of the ceiling?

Thanks for reading.

 

[Why Not Indeed]

the big floor joists hover over it by about 3mm

Given what you've said, surely the floor joists are supported by the RSJ. As soon as you put any weight on it [ie, put the flooring back down, furniture in the room, etc] the 3mm gap will disappear. Did you notice bounciness in the room before you took the flooring up?

 

[mike42]

Thanks for taking the time. I stupidly hadn't considered that. The rsj is a bit of a beast and sits on its own brick piers etc - what you say must be right. I didn't really notice bounciness but I seem to recall if I stamped in one corner of the room, tables on same or other joists might vibrate a bit.

Given what you say, would there be any harm spending half an hour putting in 1-2mm wood slices just to firm them up a little?

 

[Leofric]

There is no sag but if I put my weight on one joist and apply my weight on and off there is quite a bit of bounce.

I didn't really notice bounciness

those joists span about 4m max, steel beam will be meant to support the floor joists at mid span.