Joist sanity check

[renovationsnewbie]

I’m a DIYer fitting a new bathroom (adding a bath where there hasn’t been one before) and need a sanity check on my structural plan. The structural engineer has advised "Upgrade to minimum 150mm depth at 400mm centres".

Existing Joists: 120mm x 45mm (5x2) at 400mm centres.

End A (Masonry Wall): The current joists are pocketed into an internal masonry wall.

End B (Steel Beam): The joists are notched to sit on the bottom flange of a steel beam. The bathtub will sit on this end of the room above.

Access: Ceiling is down, bathroom above is empty.

Constraints:

1. I do not want to disturb the existing brick pockets as they are shared with the joists in the next room. I assume that face fix hangers are the best option here (unless you recommend otherwise?)

1. Using a masonry hanger at the wall end forces the new joist to sit approx 50mm away from the existing joist (due to the hanger flanges) so they can’t be glued and bolted flush.

My plan:
I plan to sister new 150mm x 50mm C24 timbers alongside the existing ones, connecting them with noggins and bolts through the noggins.

Method:

Wall End (Hanging):
I’ll use Simpson JHM Masonry Hangers face-fixed to the brickwork with chemical resin and bolts

Steel End (Bearing):
I’ll notch the new 150mm joist to sit directly on the steel bottom flange.

Connecting the noggins and joists:
Because of the 50mm gap, I will use solid timber blocking (noggins) between the old and new joists.
I’ll use M12 threaded bars with 50mm square plate washers bolted through the blockers every 600mm along the span to prevent buckling/twisting.

The images are my sketches of what this will look like on each side, one against the wall, the other against the steel beam.

Please let me know your thoughts!

 

[Dereekoo]

The supports at each end look OK. If SE says upgrade to 150 x 50 I assume he is discounting any assistance given from the existing joists and in theory these could be taken out altogether??? Obviously leaving them in will give you a stronger floor but trying to sister the new joists to the old joists will not make the floor any more stronger than it would be without the sistering. I assume the RSJ has been designed to take the standard floor loading and any extra load (if any) that the bath may impart on the floor

 

[StephenStephen]

Speaking as an amateur:
Why not just put the new joists half way between the old?
Is the SE asking for bolts and noggins? That all seems a little OTT to be honest, unless you're planning to bathe in plutonium.
You might find (with advice from others on here or look at span tables) that having 200mm centres (with new and existing joists in place) that you don't need as much as 150mm depth.

 

[Dereekoo]

Speaking as an amateur:
Why not just put the new joists half way between the old?
Is the SE asking for bolts and noggins? That all seems a little OTT to be honest, unless you're planning to bathe in plutonium.
You might find (with advice from others on here or look at span tables) that having 200mm centres (with new and existing joists in place) that you don't need as much as 150mm depth.

Doesn't make any difference structural wise whether the old and new joists or next to each other or equi spaced.

 

[renovationsnewbie]

The supports at each end look OK. If SE says upgrade to 150 x 50 I assume he is discounting any assistance given from the existing joists and in theory these could be taken out altogether??? Obviously leaving them in will give you a stronger floor but trying to sister the new joists to the old joists will not make the floor any more stronger than it would be without the sistering. I assume the RSJ has been designed to take the standard floor loading and any extra load (if any) that the bath may impart on the floor

Thanks so much for taking the time to reply.

Do you suggest basically just adding new ones in between in leaving the old ones as they are? Do you think I should go for masonry hangers that face-fix with bolts or the type that you fit into the mortar line, then slate pack it?

Thanks again!!!

 

[renovationsnewbie]

Speaking as an amateur:
Why not just put the new joists half way between the old?
Is the SE asking for bolts and noggins? That all seems a little OTT to be honest, unless you're planning to bathe in plutonium.
You might find (with advice from others on here or look at span tables) that having 200mm centres (with new and existing joists in place) that you don't need as much as 150mm depth.

That would make my life so much easier. The SE is a bit slow, very good with calc but a bit bad with the practical works..

 

[noseall]

I’m a DIYer fitting a new bathroom (adding a bath where there hasn’t been one before) and need a sanity check on my structural plan. The structural engineer has advised "Upgrade to minimum 150mm depth at 400mm centres".

Existing Joists: 120mm x 45mm (5x2) at 400mm centres.

End A (Masonry Wall): The current joists are pocketed into an internal masonry wall.

End B (Steel Beam): The joists are notched to sit on the bottom flange of a steel beam. The bathtub will sit on this end of the room above.

Access: Ceiling is down, bathroom above is empty.

Constraints:

1. I do not want to disturb the existing brick pockets as they are shared with the joists in the next room. I assume that face fix hangers are the best option here (unless you recommend otherwise?)
2. Using a masonry hanger at the wall end forces the new joist to sit approx 50mm away from the existing joist (due to the hanger flanges) so they can’t be glued and bolted flush.

My plan:
I plan to sister new 150mm x 50mm C24 timbers alongside the existing ones, connecting them with noggins and bolts through the noggins.

Method:

Wall End (Hanging):
I’ll use Simpson JHM Masonry Hangers face-fixed to the brickwork with chemical resin and bolts

Steel End (Bearing):
I’ll notch the new 150mm joist to sit directly on the steel bottom flange.

Connecting the noggins and joists:
Because of the 50mm gap, I will use solid timber blocking (noggins) between the old and new joists.
I’ll use M12 threaded bars with 50mm square plate washers bolted through the blockers every 600mm along the span to prevent buckling/twisting.

The images are my sketches of what this will look like on each side, one against the wall, the other against the steel beam.

Please let me know your thoughts!

All looks very faffy.

Cant you just infill between the existing joists at the wall end with solid timber noggings, fixed to the existing and screwed to the wall then fix your joists to this and bolt through existing? You could add a framing angle on the exposed side....

 

[DAZB]

My solution would be to noggin between the joists with 6 X 2 timbers fixed with heavy screws or anchor bolts and skew fixed into the current joists then rip 30mm lengths from another 6 x 2 and use foaming glue and 6 X 100 screws or the TurboCoach screws (https://www.screwfix.com/p/turbocoach-hex-flange-coach-screws-m8-x-70mm-50-pack/38295) sunk flush to fix to the underside of the existing joists taking them up to 150mm and then joist hanger under them fixed onto the new noggins fully nailed with galv twist nails, job done with minimal timber and no spacing issues .

 

[cdbe]

As another amateur, if the existing joists aren't in danger of shearing at the ends, surely the sisters are just to reduce deflection mid span so don't need to bear on the walls, although it looks easy enough to notch one end into the rsj.

 

[Dereekoo]

All looks very faffy.

Cant you just infill between the existing joists at the wall end with solid timber noggings, fixed to the existing and screwed to the wall then fix your joists to this and bolt through existing? You could add a framing angle on the exposed side....

Or just fix the noggins in place as above and put joist hangers to support the new joists a bit like numerous ledger boards