Can I drill a joist near the wall in order to sister it?

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Gary111

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Hi, I have a slightly rotten bathroom floor joist.
Can I drill maybe 2 x 10mm holes near the end where it sits on the wall, so that I can bolt a sister onto it?

A lot of things I have read say not to drill holes near the end, I assume they mean for cables and pipes, but does this apply to trying to strengthen the joist?

Failing that I could try 6.5mm structural screws?

Any advice would be great thanks.
 
No, you shouldn't drill holes nearer than about 300mm. I have to wonder why you want to do this, though. Structural screws do not replace coach bolts, and therefore should not be used for this purpose - coach bolts should be set at distances apart greater than 600mm along the full length of the joist

How were you intending to support the ends of the sister? What size is the original joist?
 
Thanks, I am thinking of using some flat steel plates screwed onto the sister so that I can slide it down the side of the exiting joist into the pocket.

Either that or use something like bower beams with the bottom cut off so it's just a flat plate as I don't think I can get the bottom under the existing joist.

It's under the bath so access is tricky.
 
Do you need to reinforce it if it is only slightly rotten. Better maybe to brush off any loose or flaky wood, treat the joist with wood hardener , and build up with epoxy.

Blup
 
Hi, thanks for your help, can I please clarify that if I want to sister a 3 x 5 joist which is 5 and a half feet long.

I shouldn't bolt for 12 inches either end and bolts should be no closer than 24 inches?

So I should only use 3 bolts on the whole length?

I am using m12 coach bolts

thanks
 
JobAndKnock said:
No, you shouldn't drill holes nearer than about 300mm. I have to wonder why you want to do this, though. Structural screws do not replace coach bolts, and therefore should not be used for this purpose - coach bolts should be set at distances apart greater than 600mm along the full length of the joist

How were you intending to support the ends of the sister? What size is the original joist?
Click to expand...
From this
 
Gary111 said:
I shouldn't bolt for 12 inches either end and bolts should be no closer than 24 inches?

So I should only use 3 bolts on the whole length?
Click to expand...
Oops! My previous post should have read "no further apart than 600mm". No idea what happened to that, but a fair guess that it was just a case of big fingers, small phone screen. Sorry for any misunderstanding. The standard I've worked to on a number if projects (i.e. many thousands of joists sistered) calls for this plus a minimum of 300mm from the last bolt to the end if the sister joist (which has to be supported at the end on a minimum 50mm bearing surface)

This means on something like an up to 8ft sister you'd need three bolts
 
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