Joist spacing

[RogerS]

Laying some new 20mm oak T&G floorboards onto 18mm structural ply and was wondering what sort of spacing I can get away with. These are 300 year old joists and I'm sticking firrings on as they've sagged over time. Just that a few, the spacing is about 80cm and I'd rather not faff about putting noggins in etc.

I reckon I'll get away with it?

 

[PAC1]

How big are the joists and what is their span?

 

[MikeG.]

Roger,

I'm not quite following. You have put ply down onto an existing wooden floor to stiffen it up? Now, are you planning on firrings on the top of the ply, or underneath?

In principle, older floors are usually a bit too weak anyway, and if you don't trannsfer the load evenly to all of the existing joists you necessarily increase the loading to some of the others. This is clearly not a good idea.......make as much contact as you can.

Mike

 

[Willis]

If you give me the spans and diamenter of exisiting timber and width apart I can tell you the size needed, otherwise ask building control they will tell you instantly.

I am only in kidderminster (notice your in worcs) the building guys are pretty good

M

 

[RogerS]

A picture's worth a thousand words!

Apologies for the shaky picture.

The joists are 300 year old oak - either 6" x 6" or 4" x 4" - and as you can see the span is quite short - about 7ft. I'm not worried about these joists but as you can see they sag in the middle. So I'm bolting firrings to the sides to give me a level playing field.

Then the 18mm ply is going on top so I don't need to worry about trying to find fixings for the floorboards - overkill I know..I could in all honesty and given the dimensions involved simply fix the oak floorboards dirctly to the firrings.

But, as planned, the oak floorboards then go on top of the ply. The distance between the joists is to my eye perfectly reasonable. It's just that on the far side of the second joist in the picture, there is another smaller joist that is quite small, very round but stops me from fixing a firring to that side of the 6x6 joist. That means that the distance from the firring on the next joist in and this 6x6 is about 70cm - give or take.

 

[OLD]

You could get creative with the 6x6 and say fix shaped pads to the top of it to get it level. Not to difficult when the other firings are in cut with the band saw .The proposed ply and oak floor thickness should span your greatest distances any way.

 

[RogerS]

You could get creative with the 6x6 and say fix shaped pads to the top of it to get it level. Not to difficult when the other firings are in cut with the band saw .The proposed ply and oak floor thickness should span your greatest distances any way.

LOL...yes, that's probably what I'll end up doing. Only problem is that, naturally, the top of the beam isn't level in any direction for more than..oohh..a couple of mm. Probably time to get my knackered old Bosch planer out.