Joist sistering advice needed

[figurinitout]

Hi all. I'm looking for some advice regards sistering joists in a bathroom.

Basically, I'm looking to reinforce the joists that the bath will sit on. Existing joists are 63x175 (yep, 175 and not 170 so won't get perfect snug match with any new timber but a few mill here or there won't matter, I'm sure). Joists are at 400 centres (a few mil give or take here and there) and the span is just shy of 3.7m so within code.

Am looking to reinforce the joists that will sit under the bathtub which is moving from its previous position centre-span running in line with the joists to a corner spot running perpendicular to them.

Problem I have is that approx 1m along the length is a non-load bearing stud wall which absolutely cannot be removed. And that's going to prevent me from getting the new joists in to position. I was thinking of cutting the lengths and attaching them from both sides of the stud wall and splicing them with say a metal splicing plate. Would this be OK?

One final consideration is that I can't easily seat the sisters onto supports with risking disturbing brickwork that I'm loathed to disturb. Is it sufficient to sister to 'near' the end but not actually support? I understand this wouldn't give the same support but would it still give a good amount of assistance to deflection prevention?

Thanks in advance

 

[Wayners]

Do the best you can that you think will work.
It's difficult to get joists in without gutting the place sometimes

 

[ree]

OP,
Why not show a pic of the joists?
Usually there's no need for doubling joists under a tub - your hefty joists appear to be more than adequate.
You could always screw rippings of 18mm or so ply to the joists no need for bearings - a ripping of ply will stiffen up the joist. And the sheet of ply or MDF etc sub-flooring will spread the weight.

 

[figurinitout]

Don't have pics to hand, will try and upload when I get chance but reason is that I'm adding a fair bit of weight with new floor tiles but, probably more importantly, it's because that's what Building Control told me I should do and I feel I should probably do what they've told me I should do, lol.

 

[Notch7]

Is it sufficient to sister to 'near' the end but not actually support?

Yes it is.

Problem I have is that approx 1m along the length is a non-load bearing stud wall which absolutely cannot be removed. And that's going to prevent me from getting the new joists in to position. I was thinking of cutting the lengths and attaching them from both sides of the stud wall and splicing them with say a metal splicing plate. Would this be OK

Not much point fitting the 1 metre part, just do the longer length.

 

[robinbanks]

that's what Building Control told me I should do

Did they do that in writing? Quite unusual for a BI to get involved in design and tell you what to; normally the response is "ask your structural engineer and show me the drawings"

As to whether your floor will support your tiles and bathtub, work out how many square metres your bathroom is ask that number of your rugby playing mates to come round and stand in the bathroom, evenly spread out round the room. That's representative of the dead load permissible. Is what you install in the bathroom really going to weigh more than that?

 

[figurinitout]

Haha, I shall be sure to tap up the local rugby team.

Building Control didn't put anything in writing - they didn't actually require approval for the renovation but did call me to tell me approval wasn't needed but advise of things I need to do to be compliant with regs and one of those things was the doubling of joists below tub. Not sure exactly what reg that is or if that's a belt and braces thing but figured i should probably take notice.

Joists are currently in a pretty decent shape, no visible signs of deflection/sagging. One of the joists squeaks a bit when stood on but I think that's because it's twisted slightly and the squeaking is the pulling on an adjacent noggin. Will be rectifying that by putting noggins on the other side of that joist.

If sistering around 3/4 the way is likely enough then that'd suit me just great. As you can tell, I don't have a structural engineer to ask

 

[cdbe]

If it's going from mid span bearing on (probably 2 joists) to against a wall and bearing on probably 4 joists the loading should be significantly reduced. Also, those size suggest "old wood" which is generally stronger than modern fast grown stuff.

 

[figurinitout]

Oh yeah, it'll be old wood alright; Victorian property built around 1890 so a good age to it. To be honest, if it weren't for the Building Controller comment, which was probably just a generic statement anyway, then I'd probably not give it much thought. May well be worrying unnecessarily.

Think what I'll do is sister as far as I can the timbers in so that I can be happy I've provided  some additional strength and try not to worry too much more about it as its slowing up the whole project.