Joining joists together, building code

[^woody^]

At court you would need an expert witness to comment on the connection.

Such a person could state that the joists can be joined together with 4" nails if that was his opinion and the judge would accept that over the opinion of a non expert who's opinion that bolts and washers were needed.

 

[Bouy]

That is not structurally sound, joining joists together when they are destined to take/transfer bending moments is not a standard practice , a longer joist being the best option and certainly is not something a builder is capable of designing. Here's a little light reading but if its to heavy just look at the pretty pictures of the tested beams and how they failed.https://www.google.com/url?sa=t&rct.../21/9288/pdf&usg=AOvVaw00oArXstsxtJRVkMYuuAV3

 

[Bouy]

A lighter read
https://www.google.com/url?sa=t&rct...163/download&usg=AOvVaw0ONEK2LIX28THHN-xtJ6mp

 

[DartArms]

Thanks @Bouy that's interesting.

So am I right in concluding that if someone was to join some joists together in this fashion they should be getting a structural engineer to calculate how this would need to be done. So in most cases it's cheaper, simpler and better practice to just replace the entire span with a single continuous new joist?

There was no reason in my case why a new joist could not have been fitted, it was the builder who chose not to. I'd actually asked him to replace it with a single joist spanning the whole distance.

 

[Bouy]

You could always ask for his calcs regarding the joint and see what he comes back with other than "I've done it like this loads of times and never had a problem". Blind him with science, the max bending moment at the centre of the beam based on standard floor loadings and say 500mm joist spacings would be 1.5knm, at the joint the bending moment would is about 2/3 of this and the joint would need to be capable of transferring this between the 2 joists. He probably won't know knm is kilo newton metres or the difference between a bending moment and a magic moment but at least you will have asked pertinent questions and have something to come back with in the case of failure. I don't think just modifying just the one joist will lead to a catastrophic failure as there tends to be a fair bit of safety factors within floor joists design but it may cause niggling issues like excess deflection in the future when he will be long gone. Good luck.

 

[jeds]

It's pretty common practice these days to use structural screws rather than bolts. I'd agree that those joints aren't ideal but if it came to an argument I'd bet they could be justified - structurally I mean.

 

[tony1851]

It's pretty common practice these days to use structural screws rather than bolts. I'd agree that those joints aren't ideal but if it came to an argument I'd bet they could be justified - structurally I mean.

Precisely: this is why I suspect the OP would be on difficult ground trying to prove it wouldn't work. All his builder would need was an SE to do the numbers to show there's no issue with it.
Many years ago when I was starting out, a developer said to me that you can prove alnost anything with figures if you take them to the nth degree.
Since that time, I've learned that he wasn't far out.

 

[Bouy]

Precisely: All his builder would need was an SE to do the numbers to show there's no issue with it.

Unfortunately as far as I'm aware there isn't any data put forth anywhere as to the safe tensile stress properties perpendicular to the grain of the timber so it would be quite interesting to see how the bending moment forces at the bolts/screws/nails or whatever, when resolved into the vertical direction, lead to a calculation showing that the wood would not split along the grain of the wood, but thenthese SEs are a clever bunch

 

[clifford1]

Why is there a gap with the joist cut away? Has a section been cut out for some reason, or has it always been like that?

Wouldn't it have been a better idea to put in sub-joists (whatever they are called ?) across the ends of the cut off-joist fixed to the two adjacent joists, and then put in a new shorter joist to bridge the gap? Then the weight would be shared with two full length joists.
All our upstairs fireplaces are like that - one joist cut away and the replacement structure supports the weight of a heavy slate hearth slab filling the gap.

 

[Notch7]

sub-joists (whatever they are called ?)

trimmer

 

[clifford1]

trimmer

That's the word - thanks.
Also used when cutting a hole to put in a staircase.

 

[Bouy]

Wouldn't it have been a better idea to put in sub-joists (whatever they are called ?) across the ends of the cut off-joist fixed to the two adjacent joists, and then put in a new shorter joist to bridge the gap? Then the weight would be shared with two full length joists.

No. The weight is already shared by the full length joists by virtue of the floorboards crossing at 90 degrees

 

[catlad]

Anyway the lesson learnt is don't put all your screws in a line!

 

[Nakajo]

And I wish we had a word for things 'viewed from above'

 

[Notch7]

Problem sorted: