Strengthen Floor Joists from beneath

[coldmonkey]

Hello,

I have recently had to have my entire bathroom replaced due to water damage from leak including the floor (changed floor boards to 75mm ply due water damage). I was told that joists were ok, although I now have reason to suspect that they could do with strengthening.

If possible I'd like to do this by going through the ceiling below (i.e. pulling it down) because I don't want to take my only bathroom out of action (and pulling up floor tiles is a nightmare). My concern is that by going from underneath I won't be able to screw the floor boards to the sister joists very easily, which leaves me wondering if glueing the top of the joist to the floor from under neath and using right angled brackets that will allow me to screw upwards will be good enough to re-secure the floor (if it has, I suspect, come slightly away from the joists). I would secure the sister joists to the original either with screws or bolts.
Does this sound like it would work? Are there better ways of doing this?

Thanks.

P.S. The joists are not rotten, I'm just concerned that the plumber has weakened them by cutting too many notches out of them.

 

[foxhole]

You could double up joists or reinforce with 22mm ply if span is small enough, no need to fix to floor boards as you are supporting them and they are fixed to current joists.

 

[big-all]

assuming your sistering say 8x2" joists why not just sister with 6x2" then you can save all the notching that will reduce the strength pretty much to whatever the notch is anyway

go for no10x3.5"[5mmx90mm]every 8 to 10" staggerd top and bottom

your notches should be no more than 1/8th the depth or 1" on an 8"joist

 

[coldmonkey]

Thanks for the replies. I'm trying to fix the new joists to the floor because I'm worried that the plywood floor has been slightly unscrewed by the bouncing - this is just a theory to try and account for the occasional faint 'pop' sound that I hear when moving from one side of the room to the other, although it could be coming from some of the bathroom furniture moving - I'll only know when I take the ceiling down.

 

[big-all]

is that 25mm ply or if its realy 75mm how is it made up!!!

 

[theoldun]

Take heed of what big all has told you. Very good guidance.
Highly un -likely, screws have loosened from joists. espcially when you say new 25mm ply has been tlled over. If ply had come adrift, the deflection would have popped tiles and grout by now
Popping noise most probable from bath cradle and bath.
Even if you do scissor with 50x150, doubt if you will have enough slack on electrics to get them over the top of scissor. Will have to cut, drill and rejoin.
Would not consider taking ground floor ceiling down. Would take a plumber with the hump and a chainsaw to seriosly weaken a 50x 200mm joist over a short span such as bathroom. Spend the money on the family.
Glad to see you are firing on all cylinders big all. Keep the good work up. Thought I would have a look at this forum

 

[coldmonkey]

I take the point about the popping noise being unlikely to come from the ply coming up (which is 25mm not 75mm - wasn't thinking straight when I typed that).

I'm pretty sure that the joists are 7" by 2" and there are notches out for the (22mm) central heating pipes. the feed and return for the radiator (15mm) and a cold feed pipe for the toilet (15mm).

The joists will have been like they are since whenever the heating was fitted, which was about 20 years ago I'd say (house was built in 1962 and probably didn't have CH). It's just that when my joiner was repairing a botch job in 1/4 of the actual floor (long story) he decided that it was worth beefing up the joists whilst the floor was up anyway: that section of floor is now so solid it feels like I could park a car on it.

My wife says that she can see some deflection in the floor when I deliberately bounce (not jump) on it (I weigh 17.5 stone). My kitchen still remains undecorated after the last disaster (CH pipe leak) so I've got myself into thinking that I ought to do something before re-decorating. I think I'm being paraonoid because I've got it into my head that floors should not have any deflection in them whatsoever (under any circumstances). The upside is that the ceiling below hasn't shown any signs of cracking, so I guess that's a good indication that whatever deflection there is it is not significant.

I'd rather not pull the ceiling down, but only if I can leave it and believe that it is safe (p.s. bathroom is 2.5m x 2.5 approx, with notches out of about 4 joists). Do you guys believe that I'm likely to be safe leaving this (even if I could technically reduce the deflection to almost nothing)?

Forgive me if I sound a little crazy, I've had the worst nightmare with the bathroom from when the leak below it started (cowboy tradesmen, had to move out for a month etc.) and I just worry about doing what I can to prevent any more disasters.

 

[big-all]

178mm div by 8=x7=156 so 22mm or say 26 is just a tad to much

what is the unsupported span offf the joists and at what centres are they!!

 

[coldmonkey]

178mm div by 8=x7=156 so 22mm or say 26 is just a tad to much

what is the unsupported span offf the joists and at what centres are they!!

The unsupported joists span is about 3m, they are 400mm apart.
Someone came round to give me a second opinion last night and it would appear that when I bounce on the floor the ceiling below deflects about 3mm and even with normal walking deflection can be detected. So, I've decided to go ahead and pull the ceiling down. Thanks to everyone for their advice.