Length of coach screws for floating shelf

[BennyK]

I recently made a floating shelf, roughly 2m long. It is a hollow box mounted on a timber bracket with 5 crossbars and attached to 4 studs via 10 x 100mm coach screws with washers. This means that 50mm of the coach screw goes through the 2x4 bracket and then 50mm goes back into the wall.

I have loaded it up with books, which means we are talking about probably around 60kg that it is holding in addition to the weight of the hollow box. And so far it is doing fine, but I just wanted to make sure that it would hold long term.

Do you think 10 x 100mm coach screws are going to be enough to hold this level of weight or it would be worth replacing them with 10 x 120mm coach screws or even 12 x 120mm coach screws? I didn't want to go too long or wide, since the stud is only 75 x 50mm and I didn't want to risk splitting the stud.

In any case, what do you think, should the 10 x 100mm screws hold this weight (with only 50mm of them through the wall, roughly 10mm of that plasterboard and the rest the wood stud) or should I get slightly longer/wider screws?

 

[rsgaz]

Just a single M8 coach screw 50mm long, on a stud wall, on a 600mm cantilever arm can hold me up, 82kg at the time.

I think six adults could hang from your shelf!!

 

[big-all]

what size screws did you use between the back and the ladder section ??
also looks like 38mm thick cls ??

 

[BennyK]

what size screws did you use between the back and front rails and the ladder section ??

I used 5mm x 120mm screws. Two of these in rails #1, #3, and #5, and three of these in rails #2 and #4.

 

[BennyK]

Just a single M8 coach screw 50mm long, on a stud wall, on a 600mm cantilever arm can hold me up, 82kg at the time.

I think six adults could hang from your shelf!!

That's encouraging I've been too nervous to hang from it myself ...

 

[big-all]

should be ok assuming 38mm timber thats 80mm into the timbers
assuming you are not gluing the box on a few screws into the wall support through the top at the back will give extra support further loading up the wall fixings

 

[BennyK]

should be ok assuming 38mm timber thats 80mm into the timbers

It is just a standard 2x4 CLS16, so just a hair under 50mm thick.

assuming you are not gluing the box on a few screws into the wall support through the top at the back will give extra support further loading up the wall fixings

Could you explain what you mean here ^ a bit more?

 

[big-all]

iff you fix the top along the back edge then any temptation for the legs to sag and pull out the wall plate will be further supported by the box
other wise as it sags you will get a say 6mm gap appear between legs and wall plate and a corresponding gap between top back and wall as its now 6mm short