Joining joists together, building code

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DartArms

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Hi,

Would anyone be able to point me to the relevant building code documents where it details the fixings required to join to joists together to make 1 longer joist.

It's my understanding that bolts are required in this situation but after googling I can't find the building code where this is specified. I'm probably just not searching for the correct terms to bring this up.

Thans
 
You'll be hard-pushed to find info. on that; it's not usual to extend joists to make longer joists.

If you really must, you need either coach screws or bolts with toothed washers to join timbers together, rather than just plain bolts.

It's down to a question of determining the size, type and spacing of the fixings, which is not something you can pick up on youtube.
 
Last edited:
tony1851 said:
You'll be hard-pushed to find info. on that; it's not usual to extend joists to make longer joists.

If you really must, you need either coach screws or bolts with toothed washers to join timbers together, rather than just plain bolts.

It's down to a question of determining the size, type and spacing of the fixings, which is not something you can pick up on youtube.
Click to expand...

thanks

The reason I’m asking is that my builder has done this and used normal wood screws to join the joists together. It’s actually 3 joists joined together. 1 coming out of the wall which joins into a new joist which spans the middle of the room and then joins into another joist that goes into the wall on the other side of the room.

I was after finding some info where it specifies this is bad practice, or where it states how this should be done correctly.

we have fired the builder due to numerous issues and I’m just documenting everything incase we need it in the future.
 
tony1851 said:
A diagram and/or a couple of pics would help, with note of unsupported span.
Click to expand...

I could post that tomorrow if it's really needed.

But just to be clear, I'm NOT looking for advice on how to join joists together.

I want to be able to, if needed, explain in the small claims court how the work should have been done (or why the way it was done is not up to an acceptable standard) and be able to reference some kind of official information on this thats better than "Dave on the internet said it should be done like XYZ".

How does anyone know how two joists should be joined together correctly? There must be something somewhere that says how it should or should not be done or else how does anyone know what a good or bad way of doing it is?
 
It all depends what the timber is holding.
If it's only going to be a point to fix old school lamps, what your builder did was more than enough.
Instead if it's going to be a structural support, well in that case you would need a structural engineer to calculate what's required and most likely it will be one length of timber instead of 3 together.
 
I suspect that the only instance you will see floor joists being joined in this way is in restoration work, where rotted joist-ends are cut away and short pieces fixed to the ends to replace rotten wood.

But that is only remedial work where it may be necessary to preserve the bulk of the length of joist.

What your builder has done may or may not be serviceable. Beware of taking him to the SCC; just because he's done something that doesn't look right, it doesn't mean that it won't work;as they say - there's more than one way of skinning a cat. As a start, you might consider getting a SE involved to see if he/she can 'prove' with figures that it doesn't work under normal loading.

(and my name's not Dave, btw :LOL:)
 
[GALLERY=media, 106298]Joists by DartArms posted 31 Mar 2021 at 10:17 PM[/GALLERY]

OK so here's a diagram. Along with the other joists that are full length it's supporting the floor in the room above.

I'm not planning on taking anyone to small claims, I just want to cover my back if the builder was to take me to court as we did not part on the best of terms. I've already had a carpenter, a different builder and an architect tell me they should have been bolted together, or better still simply use a single joist over the full length. It's my opinion that the only reason this was done is because the electrician had already run a couple of cables through the old joists so it would have meant re-running the cables.
 
DartArms said:
[GALLERY=media, 106298]Joists by DartArms posted 31 Mar 2021 at 10:17 PM[/GALLERY]

OK so here's a diagram. Along with the other joists that are full length it's supporting the floor in the room above.
Click to expand...

you say it is part of a floor.

is it on the ground floor, or upstairs?

How are the old and the new fastened together?

You say the span from wall to wall is 4m. How long is the new joist?
 
Screwing can be acceptable if the overlap of the timber is sufficient, the screws are of the correct guage and length, and of the correct number and spacing. This could only be ascertained one way or the other by an SE experienced in timber design, seeing the job first hand.

[Despite what you have been told, bolting in this context is not the correct way to join timbers (unless they incorporate toothed washers); plain bolted joints are subject to 'slip' once the timber shrinks]

If you are aiming to use this deviation from normal practice as a form of 'counterclaim', you might be on dodgy ground.
 
Thanks all, this looks like it's a complicated issue and not as straight forward as I thought it would be. It's only 1 out of a list of about 17 issues so I think I won't look into this one any further unless there is a need to in the future. The other issues are far more clear cut.
 
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