wet rot on attic floor joist

[JohnnyF]

I am currently gutting our house and have stumbled across some wet rot on the 2nd floor floor joist.

The area where the rot is had a shower above it (I don't think it has been used in about 6 years since the previous owners bought the house) so the rot has dried out.

The problem is the rot is in two joists (maybe the size of a 760mm shower tray). The location of the rot is by a supporting wall that is positioned in the middle of the floor joist's span (When I get home from work I'll try and upload some pictures).

I'm going to replace the floorboards but I was wondering if this sort of rot normally requires the joist to be replaced. Or can you run another piece of timber alongside the joist and bolt it in? Or strengthen it with noggins either side of the rot?

Is it a big/costly job (considering the house is just a shell and the ceiling below has been taken down so there is access from under the joist? Also would a joiner be able to do this sort of work?

 

[Deluks]

I'm going to replace the floorboards but I was wondering if this sort of rot normally requires the joist to be replaced.
Yes get rid of all rotting timber and also good practice to cut back upto 500mm of the sound timber, to be safe

Or can you run another piece of timber alongside the joist and bolt it in? Or strengthen it with noggins either side of the rot?
Yes, bolt a second alongside is standard procedure. Not noggins but a trimmer attached to joists at either side, although trimming 2 or more joists can involve strengthening of the supporting joists, so best go with the first option.
Is it a big/costly job (considering the house is just a shell and the ceiling below has been taken down so there is access from under the joist? Also would a joiner be able to do this sort of work?

About half a days work for a competent joiner, could even do it yourself with advice on here, that's why it's a diy forum. Get those pics on first though.