Need to strengthen floor joists

[therobynator]

Hi! We had a level entry shower installed upstairs on the timber floor. Builder checked out the joists & laid cement sheeting, it's all done upstairs but now 2 months later we have a leak in the corner of the shower (coming through downstairs) and an issue at the other end but I'll tackle that later.

Existing joist spans 3500mm is 50mm wide & 170mm high. Builders new joist is 1700 long, 35mm wide, 130mm high and nailed to existing (see photo).

New joist is supporting the end of the shower floor which is 1000 wide which is why it is not as high as the existing. End of shower floor is what is relying on new joist. Existing joists are 450 apart (at center) so middle of shower is ok.

Wondering which is best way to solve problem? Would like advice please.

Distance from bearer to shower base is 660 on one end & 1700 on the other end. Measurement taken from above the bearers (the beam/wall the joists are sitting on).

Should I put in a couple more joists say 3500 long, 50mm wide & 130mm high and bolt the existing + builders + new ones together? If yes where is the best place to put the bolts so I don't weaken anything?

From reading other threads I'm thinking galvanised coach bolts?

I'm going to buy the timber for the job and have a different builder do the work as the other guy is suddenly uncontactable

 

[noseall]

Are you sure that the joists are at fault?

Is there a lot of give in the base?

Are you a very heavy person?

Could it be shrinkage?

what exactly has happened to cause the leak?

 

[therobynator]

Took some closeup photos. It appears the new joist has dropped leaving fractures in vilaboard and a crack in corner.

Base is 2 layers of vilaboard, tilers mud and 12mm floor tiles.

When water went through there was approx. 150kg (2 adults). Up until then max weight up there was approx. 124kg (1 adult, 2 young kids).

Have called tiler. He'll be here tomorrow so I'll know about shrinkage etc. then.

What exactly has happened.... I'm thinking more weight than usual up there + joist not adequate for that load = joist dropping a fraction resulting in vilaboard moving/base moving in that corner.

How do I work out what load that beam has to support?

The rest of the bathroom floor runs along the same area the new joist is supporting BUT because the new joist is short the rest of the floor is not being supported by anything but floorboards! T

Thinking I'll definitely need a joist spanning 3500 to ensure the entire end of room is supported - not just shower base...

 

[therobynator]

Tiler came over. We ran shower, stood in there, walked around in there & no leak.... until 15 minutes after he went. He's coming back tomorrow.

Will post outcome for all to read