What to make herringbone strutting between joists from

[garyo]

On my plans I've said that I'll have first floor and roof level joist strutting from noggins/offcuts, and I'll certainly have the wood available to do so. However, I've just discovered the existence of these metal equivalents. I'm guessing they'll make for a quicker job, but will it be a better result (other than being easier to put cables/pipes through?)

Thanks

Gary

 

[jeds]

Go with the metal. Ten times easier and probably a better job.

 

[hammerswinger]

Can the metal ones be fitted to the sides of the joists rather than to the tops & bottoms?
If they're fitted to the top of the joist will they not have to have a rebate cut?

 

[jeds]

No need to rebate. Once the board is down you won't know they are there.

 

[theoldun]

Galvanised metal herring bone strutting is as much good as a chocolate kettle. Sorry Jed, but you are also liable to get a sqeak on your boarding when it goes over the top. of the metal.
We use either 38x38 sawn or solid strutting 50mm shallower than the joist.
If you know the secret of marking out 38x38 then they are best in our opinion however solid is the easiest and will be plenty good enough for your purpose.
If using solids, string a centre line and work each strut either side of line so that you can gun 2no 90mm nail into each end. If using joists thicker than 50mm, then run a straight line and gun on a skew 4no 75nails in each end.
If you want to know how to set out 38x38 strutting , then let us know
Regards oldun

 

[tony1851]

There is a very good reason why herringbone strutting is preferable to solid blocking between joists.
When the joists dry out once the building is in use, they shrink and they shrink far more in depth than width. This has the effect of slightly increasing the internal angle between the side of the joist and the strut (increasing from angle x to angle y in the diagram).
This means that the shrinkage of the joist causes the strut to be forced into a slightly shorter gap, remembering that the joist-centre lines stay in the same position. The strut will hardly shorten at all, so a considerable compression will build up in the strut. This force will increase the more the joist shrinks, and if all strutting is in line, it will increase the rigidity of the floor as a whole.
For this reason, timber strutting is preferable to the thin tin things from B&Q
In the diagram, the dotted line shows the joist when shrunk, and how it forces the strut into a shorter gap between the joist and pivot.

Untitled

• tony1851
• 4 May 2012
• 1

 

[noseall]

We always fix solid bridging.

 

[^woody^]

Good explanation, Tony, but the same principle applies to the metal straps too doesn't it?

A lot is theoretical though, and any strutting will do the job.

The problem with timber herringbone is the time premium for cutting and fitting, and the fact that if there is some differences in joist spacings, then precut struts wont fit, or will require individual measuring

The best option is whatever is available at the cheapest or no cost - ie off-cuts

Edit:

Whatever you choose, just remember to put the strutting in as soon as the joists are fitted, not weeks later

 

[tony1851]

The problem with timber herringbone is the time premium for cutting and fitting

Agreed. I was just dreaming of a far-off land, a long, long time ago, when they could do these things. Lutyens, Vosey, Ballie-Scott, Norman Shaw et al spring to mind.

 

[masona]

We always fix solid bridging.

Me too, I always staggered the noggins as both ends can be fixed through the back of the joist, I'm not keen on single line noggings because of the skew fixing method

 

[^woody^]

You should always aim to keep any noggins in line - whether in floors or walls

The skew nailing does not matter as it is only really to tack the timber in place. End grain nailing is not very effective in any case

 

[masona]

The skew nailing does not matter as it is only really to tack the timber in place. End grain nailing is not very effective in any case

I do both, it's a lot easier while the end fixings hold it in place for the skew fixings, can be tricky with just skew fixings sometime, although the timber herringbone is better but I have seem them split being over tighten therefore weakness the herringbone

 

[noseall]

You should always aim to keep any noggins in line - whether in floors or walls

Yes but off-setting them minimally to access fixing is hardly going to detract from their purpose.

We always measure the gap at the wall (both ends if necessary) to ensure accuracy and continuity. We align the first joist with the laser, packing against the solid wall. All the other joists are centered off this fist straight joist.

Some joists may bow out whilst other will bow in. Therefore some nogg's may be loose fitting whilst others will be tight. But at least all joists end up straight.

The last thing you want is banana shaped joists when joining plasterboards.

End grain nailing is not very effective in any case

No, but a solid bridge series of joists should not be able to spread, so in this instance end grain fixing will be ok.

 

[RonnyRaygun]

For this reason, timber strutting is preferable to the thin tin things from B&Q
In the diagram, the dotted line shows the joist when shrunk, and how it forces the strut into a shorter gap between the joist and pivot.

Untitled

• tony1851
• 4 May 2012
• 1

Good explanation, Tony, but the same principle applies to the metal straps too doesn't it?

If this theory is to be applied to metal struts, then wouldn't they be almost certain to buckle due to their narrow cross section?

 

[^woody^]

If this theory is to be applied to metal struts, then wouldn't they be almost certain to buckle due to their narrow cross section?

Tony's sketch is probably exaggerating the amount of shrinkage. In any case, there would be rotation of the strap as the top of one joist moves down, and the bottom of the adjacent joist moves up, so the actual force on the strap is not enough to buckle it