How to fix support beam

[NicKarla]

Following on from the advice from my other thread I’m am needing to add some supports similar to a few that’s there already (see red line in picture).

I have some c24 4x2 which will be used and was intending to screw them in until I read that screws are less favourable and nails should be used due to their flexibility.

The idea of hammering into my beam is concerning and with the fear of doing more harm than good I would prefer to screw. Is this really a bad idea? Is a nail gun (which I don’t have) the only way forward?

 

[^woody^]

screws are less favourable and nails should be used due to their flexibility.

How will/can a rod of metal, whether a screw or nail, fixed through two pieces of timber held tight together, "flex"? There is just no way.

Use screws, avoid banging around in a loft.

 

[NicKarla]

Thanks. I have read several comments including from your good self way back in 2013 suggesting nails over screws for this purpose.

If screws are ok is there a rule to the correct size? I’m thinking 6 x 90 coach screws as the two pieces of wood are both 2inches each.
https://www.screwfix.com/p/turbocoach-coach-screws-yellow-zinc-plated-6-x-90mm-100-pack/46700

 

[^woody^]

Yes those turbos are quite good for fitting without a pilot hole. You'll probably need an impact driver though. Or normal 4 or 5mm screws if predrilling.

 

[Notch7]

screws are less favourable and nails should be used due to their flexibility

screws are unsuitable for load bearing applications in shear -for example joist hangers

screws are fine for your application..... or the coach screws youve linked.

A carpenter wouldnt think twice about using screws for doing this, 80x5 probably (or whatever he had in the van!)

 

[NicKarla]

Yes those turbos are quite good for fitting without a pilot hole. You'll probably need an impact driver though. Or normal 4 or 5mm screws if predrilling.

When you say predrilling do you mean using a pilot hole? I don’t have an impact drill so would a small pilot hole be appropriate, eg 2-3mm?

Screwfix have these 5x80 with torx head to make screwing easier. Only down side is the countersunk head. What do you think about these or is it best to stick to the 6x90 coach screws?


https://www.screwfix.com/p/spax-wirox-tx-self-countersunk-woodscrews-5-x-80mm-100-pack/2969p

 

[^woody^]

You'll need to drill the one timber wider than the screw to allow the screw to pass through it and pull it in tight.

For the other timber, the screw may go in without drilling - some self cutters (Turbo Gold or suchlike) or twin thread may do - put some soap or candle wax on the thread and it should fly in.

Otherwise you will have to pilot the hole with a bit about 1/2 to 3/4 as wide as the screw

 

[NicKarla]

Perfect, thank you.

Lastly, would I be right in thinking that ‘A’ would be better screw placements than ‘B’?

 

[^woody^]

"A" would be better.

I'm not sure of the purpose of these, as that looks like a trussed roof, so these braces should not be necessary. If these are a necessary structural function then they should be fitted with a single coach bolt, square washers and a spur washer (timber connector) between the timbers. But if these are not really necessary (ie not specified by a qualified person) then screws will be fine.

 

[jake7462]

screws are unsuitable for load bearing applications in shear -for example joist hangers

How is a screw unsuitable for applications in shear???

 

[NicKarla]

"A" would be better.

I'm not sure of the purpose of these, as that looks like a trussed roof, so these braces should not be necessary. If these are a necessary structural function then they should be fitted with a single coach bolt, square washers and a spur washer (timber connector) between the timbers. But if these are not really necessary (ie not specified by a qualified person) then screws will be fine.

The purpose is to add structural support. It isn’t critical but the end of the roof has been put up badly. It looks like they just added a few ends on. I’ve been advised that it would ‘help’ in the event of heavy snow and for long term durability.

Im more than happy to drill a hole and put a bolt through but I thought that drilling holes 10-12mm for a coach bolt was a bad idea as it can effect the structural integrity of the trusses.

 

[^woody^]

I can't see how a collar is going to help a truss, and certainly not one that far up. But 10 or 12mm hole is not going to may any difference.

 

[NicKarla]

Ok thanks. I don’t know what you mean by a collar but the trusses weren’t particularly well put together at the top. The cross beam holds everything together better.

So, 10 or 12mm coach bolt, one of these https://www.screwfix.com/p/sabrefix-m12-timber-connector-galvanised-dx275-50mm-x-50mm-50-pack/99094 between timbers, then one of these https://www.screwfix.com/p/sabrefix-m10-square-plate-washers-galvanised-50mm-x-50mm-50-pack/9891h on the other end next to the bolt?

 

[Notch7]

How is a screw unsuitable for applications in shear???

screws are hardened and vulnerable to breaking under high shear stress

wire nails bend a bit

 

[jake7462]

screws are hardened and vulnerable to breaking under high shear stress

wire nails bend a bit

Agreed you might get a bit more bend from a nail compared to a similar sized screw, but completely wrong to say that screws are 'unsuitable' for shear loading...