Adding noggins between joists

[paulg1]

I'm adding a some noggins mid span on a first floor to try to stiffen the floor up a bit.

The joists are 47x200mm (400mm centres) and I have some 47x170mm to nog with. Plan is to stagger the noggins and screw through the existing joists straight into the end of each noggin. Was planning on using 6x110mm screws. I have an impact driver, but if necessary I'll do a pilot hole too.

Is there any best practice on how this should be done? Does anyone have any advice on how many screws I'd need for each join?

I'm thinking three screws at each end. One halfway up the noggin and the other two at the 1/3 and 2/3 points.

 

[vinn]

If its possible, what i would do is to fix the noggins in a straight line, i wouldn't stagger them.
Use four screws at each noggin end, two "skewnailed" on each side.

Whats the span of the joists? Why are you stiffening the floor?

 

[paulg1]

3.8m span. I'm stiffening it because there is a bounce when walking across it. Bounce seems to be in the joists - not the floorboards which are well screwed down (and not squeaky)

 

[vinn]

Can you see where the joists rest at each joist end? Are the tails firmly fixed in wall pockets or hangers?
Construction glued and screwed 22mm T+G ply would make the firmest sub-floor but if you already have sub-flooring just glue and deep screw what you've got. Problem might be with gluing sub-floor down its difficult to later lift the fixed boards.

In difficult and awkward situations its sometimes works to screw and glue rippings of 22mm ply sistered against each joist. But thats a bit radical.

 

[paulg1]

Thanks Vinn,

Is skewnailing particularly difficult?

I've lifted half the existing 18mm T+G chipboard and I can see the joists at each end and they're very firmly in wall pockets. No sign of damp or rot or anything either. I did seriously consider replacing the subfloor with ply, but cost becomes an issue. My current plan is to replace it with 22mm T+G chipboard. I'll be gluing at the tongues and on top of the joists and screwing in with these: http://www.screwfix.com/p/spax-flooring-screws-4-5-x-60mm-300-pack/88716

Supplies are already bought at this point (just letting them acclimatise indoors) so I'm pretty much committed unless anyone really disagrees.

(Happily I think I can use the old 18mm stuff to roughly board the loft).

 

[vinn]

Good, just do what you are doing. After fixing the noggins then loose lay some boards and walk across them to see if the bounce is still an issue.
You could pilot drill the screw holes before setting the noggins. You could even pre-set the screws in the noggins before setting them between the joists.
Chuck a bit in your drill and use your drill as a power driver.

 

[paulg1]

You could even pre-set the screws in the noggins before setting them between the joists

That's a good idea.