Remove bounce from a suspended floor

[Sharmang]

Hi,

I want to reduce the bounce in my suspended timber floor in the Dining room. The floor has overlay screeded UFH with an engineered wood finish and will bounce slightly if you are in the middle of the room.

I have access from below via a basement, where the joists are approx 230mm x 45mm at 400 mm centers over a span of around 4.2 meters with 100mm purchase either side.

So far I have placed a row of noggins around 1/3rd of the way across the floor and 'sistered' one of the joists with a piece of C16 220mm x 45mm timber, but the floor still bounces.

In terms of next steps, I am thinking of getting a flitch beam ordered and was wondering if anyone has used this on a suspended timber floor with success?

If so, what dimensions have you used? I was thinking 150mm x 8mm (450mm staggered holes) at 4.2 meters as this will weight 40kg so can be man handled into place. Without going into the annoying costs of structural engineers, has anyone done anything similar with good effect? Potential I could order two and place them both 1/3rd of the way across the room.

Any thoughts would be appreciated.

 

[Dereekoo]

With C16 joists and a dead load of 1.25 it would just be within regs with a deflection of 12mm although it would be just ouside strength requirements. Strutting should have been fixed at halfway. Sistering one joist is not going to do anything unless your room is 1.2 m wide and its the middle joist you sister. I assume you mean putting the flitch beam across the middle of the floor so the effective span of the joists is 2.1m. If so and assuming the flitch beam is man enough then the deflection of the 2.1m joist max deflection at the centre would be less than 1 mm using the same 1.25 deadload.
Now for the flitch beam, can't help you on that as its proposed span is not given and how would you support it at its ends

 

[Sharmang]

Hi,

Thank you for your speedy reply - really appreciated!

Attached below is a diagram of what is there currently and what I was proposing to do. A run of herringbone goes along the center of the floor. I was planning on the flitch beam running alongside one of the current joists and then sandwiching it with another joist alongside (in a similar way to how I have sistered the other joist).

Would this not work? I am keen to avoid having a beam in the floor below as I want to do a basement conversion at a future date.

Many thanks,

George

 

[Dereekoo]

You are strengthening 2 joists which will make the floor more rigid in that area with a bit of overspill assistance to the joists either side of it but basically you are not strengthening the floor as a whole. You may as well put the same size joists in at 200 centres at least the deflection would reduce by half

 

[Notch7]

If you wanted to use a flitch beam and keep it within the existing joist height, you would need to cut every joist, fit the flitch beam and use joist hangers

alternatively sister every joist, maybe both sides for the joists around the middle.

and noggins help: use timber full depth of joist ie 220mm and stagger them so they can be screwed through and not just spiked

 

[Sharmang]

Hi All,

Thanks for the various suggestions. I think I will start by completing the staggered noggins at both thirds of the way along the joists and see the impact that this has.

If I need to reduce the bounce further, I will look at a flitch beam in the middle to halve the span as the ultimate solution but a fair amount of additional work.

Thanks again for all the input

 

[Dereekoo]

Hi All,

Thanks for the various suggestions. I think I will start by completing the staggered noggins at both thirds of the way along the joists and see the impact that this has.

If I need to reduce the bounce further, I will look at a flitch beam in the middle to halve the span as the ultimate solution but a fair amount of additional work.

Thanks again for all the input

Please report back on your success, or not, with the noggins as I am a sceptic on the their use in reducing deflection unless the joists are whipping over sideways on their bottom face and altering their orientation to the vertical to such an extent that their geometrical properties are adversely affected.