Joist sistering without coach bolts

[Reynardine]

I want to attach timber to the side of my existing joists to make them wider. My existing joist width is ~80mm and I want to double this with to approx 160mm. The new structure will need to support a heavy Victorian lath/plaster stud partition. The partition runs parallel to my joists.

Q: Can I use materials other than coach bolts to do this "joist sistering". My preference is to use some beefy M10 coach screws, 150mm long, screwed into the centre line of the existing joist at 300mm intervals.

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• Reynardine
• 23 Jul 2008
• 1

Any suggestions welcome. cheers.

 

[Shytalkz]

Alternate the head and point sides, put them at staggered 1/3 depth (rather than mid depth) at nominal 600 centres and make sure the new joist sits on the end bearings as per the existing joist.

 

[Reynardine]

Thank you for your guidance.

600 centres + staggered 1/3rd instead of centre line = can & will do.

Alternating point and head sides is a problem for me.

The stud partition hanging above the joist gap is so wide that it acts as a "mini- ceiling" above the joists. I don't have access to the "inside of the joists". I can only practicably work from the outside of the joists. This was my reason for avoiding coach bolts. It's hard to describe without a photo but I've lost my digi camera.

Summary : Apart from perhaps one screw at the accessible end , I cannot alternate. I can only screw in the coach screws from one joist side

 

[Shytalkz]

No problem - as long as the new joist has a bearing at either end, then the connection detail is only a nominal one and you can do from one side. You could also just nail 'em together in that instance, if you wanted: it's a connection only to get them to give some semblance of working together, that's all.

 

[Reynardine]

Got it.

I'm planning on using big coach screws, say M16 x 200mm

But these big screws might split the joist as I wrench them in.

As a precaution, should I drill 10mm pilot holes first to take the M16 screws ?

 

[Shytalkz]

You don't need 16mm, the 10s will bemore than fine.