Repairing rotten joist end

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I hope someone can advise me on this, it's structural so I'm nervous!

Shower has leaked over many years and the ends of two joists have rotted. About the top third is gone from the wall to about 10cm along the joists. I've found a place that sells repair plates (http://www.joist-repair.co.uk/joist_repair_shop.htm) and it looks simple enough. However, what do I do to support the joist while fixing? I'd rather avoid hiring acros and putting them in the room below, the ceiling is fragile. Is it ever possible to knock the metal plates into position, bolt them in place and then somehow remove the rotten wood?

Secondary question - do you put a bit of wood in the emtpy bit? I'd have thought it would be necessary to brace the plates against futue movement of the house, which is Victorian.

Thanks in advance,

John
 
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If there is space either side of where the damaged joist rests on wall on beam then an alternative method is to bolt new timber several feet long both side of the damaged joists. The new timber then takes the weight.
 
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Thanks. I've just had a really helpful conversation with David at joint-repair.co.uk and I think I'll go with the metal plates. He convinced me of the wisdom of supporting below using a solid insulation batten as a shock absorber.
 
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You don't need to remove the rotted wood in this instance since the moisture was coming from the shower rather than from outside, i.e you have stopped the ingress of water. Typically you would do what Bernard says and just bolt a new piece to the side of the existing joist and insert into the wall. No temporary support needed.
 
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No, not now you have eliminated the water source. It will just dry out. Assuming the shower really was the cause.
 
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The rot looks like pictures I've seen of wet rout, and for sure there was leaking right where the joist is. It would certainly be easier not to remove it, I guess I will know if the section I put the bolts in is sound by looking at the sawdust when I drill pilot holes.

So potentially I could position the metal plates, mortar them in and not worry about supporting below because the intact part of the joist will stay in position?
 
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So potentially I could position the metal plates, mortar them in and not worry about supporting below because the intact part of the joist will stay in position?
Exactly. The joist are clearly 'strong enough' even in their current slightly rotted condition. You're just making them stronger. You only need to saw them off if you think you have penetrating damp from outside that cannot be stopped.
 
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