Repair over notched joists

[Sadsyndrome]

Sorry for long post but I thought some background is useful. I wondered if anyone has repaired joists due to overnotching etc?

My house is a 1980s semi with first floor joists mm) in the party wall spanning about 3.8m to a 100mm block built internal wall (as  per diagram). There is an extension that contains our bedroom but that isn’t related to this issue, except it means we don’t use the upstairs in the original house much.

 

The landing has a few pipes running across the jjoists. They always rattled against the underside of floor,  so many years ago the shower pipes feeding a pump were changed to plastic and fed through new holes in the joists, to try and reduce noise and vibration.

 

The upstairs on that side of house is not used much in recent years as children flew the nest. This summer they visited and mentioned the floorboards were very creaky in landing. The living room below was decorated a couple of years ago and ceiling artex plastered over. There are no cracks in ceiling below these overnotched joists.

 

However, given the joists (5 I think) have holes drilled below the original notch I guess I should strengthen them. The holes are certainly not in the permitted area of the joists anyway.

I don’t know how the joists have survived so long given they have been butchered so badly!

 

the options I think I have are:

 

1.   Replace complete joists :(not feasible without dismantling upstairs and downstairs and nowadays joists shouldn’t go in party walls anyway)

 

2.   Full sister ( not practical as above)

 

3.   Partial sister from about 1.2m from bearing on internal wall ( using M12 bolts)

 

4.  18mm ply glued and screwed to both sides of joist on the last meter of the joist  that sits on internal wall.

 

5   I googled joist repair uk. I saw one company who sell some metal straps to stick on the side of the joist with epoxy resin. they also do bower beams.

 

This  is my preferred option (if it actually works) because I would not have to re-route the pipes that go through holes in the joist and also a couple of cables as well.

 

Does anyone have a view as to whether sticking metal straps on the side of a joist would provide sufficient strength for the butchered joists and whether it’s is acceptable for current building regs?

 

Also, any advice on screw/ bolt patterns and whether glue is required for other solutions would be appreciated.

 

I haven’t lifted carpet and floorboard (chipboard) yet,  so I attach a diagram rather than photos.