Notching joist work around

[0Floz0]

Hi all

Got an issue with a joist obstructing the shower waste we want to put in. Tried looking at different shower trays for different placements but every one seems to hit a joist. So this is the best option. I’ve already got the shower tray and enclosure so changing them isn’t an option as I can’t return them.

The red arrow in the picture points to a pencil mark where the shower waste needs to cut into the joist. Joists are 75mm thick. Total span is 1.8m and it’s also got the original ceiling joist tied into it (it’s a loft conversion and goes into a steel on one end).

How much could I take out of it? It seems like there are lots of joists as spacing is 240mm and 330mm either side of the joist I want to cut.

Just after thoughts and opinions.

Thanks

 

[foxhole]

Raise the shower base?

 

[0Floz0]

Raise the shower base?

Can’t unfortunately. Ceiling is already 2m high so very little room.

 

[blup]

If you cant safely notch joist, run waste parallel to joist, drop down internal wall to suitable point at which to exit to soil pipe. Or put in false ceiling below for same purpose.

Blup

 

[Dereekoo]

Whats the joist depth

 

[0Floz0]

If you cant safely notch joist, run waste parallel to joist, drop down internal wall to suitable point at which to exit to soil pipe. Or put in false ceiling below for same purpose.

Blup

I can’t. The joist obscures the hole in the shower tray so I’ve got to cut into it.

Whats the joist depth

220mm

I’ve added some more pictures. It feels like the joists are way over spec.

The red lines are joists that have 1.8m span as they stop at the stairs. The purple are 4.8m spans as they go to the other steel in the loft.

Red top and middle spacing is 240mm
Red middle and bottom is 340mm.

 

[cdbe]

75x220 joists with a 1.8m span - notch away!

 

[0Floz0]

75x220 joists with a 1.8m span - notch away!

That’s what I was thinking. But how much could you take off? Annoyingly it’s pretty much in the middle of the joist. Was wondering if I stuck some 3x2 the other side and screwed that in to add some strength?

 

[blup]

About 1/8th depth normally but taking into account they are over engineered, shouldn't be a problem.

Blup

 

[0Floz0]

About 1/8th depth normally but taking into account they are over engineered, shouldn't be a problem.

Blup

But I couldn’t take out say 100mm could I? Or would that be fine if I stuck some 3x2 on the other side to compensate for it?

I’m going to stick a load of noggins in as well as im tiling and so trying to reduce any movement.

 

[John D v2.0]

It's mostly bending stress at the middle and little shear. You would need to leave at least 100mm in my non professional opinion purely based on the fact that 4 by 2 joists would be just about ok for that span (but ask your friendly structural engineer)
Just make sure there's no big knots in the area-technically the joist loses its grading if you make lengthways cuts
Having ply screwed to the joists after notching would help with stiffness if you can spare the headroom. You would also have to cut the ply of course
Good luck...

 

[blup]

But I couldn’t take out say 100mm could I? Or would that be fine if I stuck some 3x2 on the other side to compensate for it?

I’m going to stick a load of noggins in as well as im tiling and so trying to reduce any movement.

Well your waste max is about 46mm?, so two inches off 9" is still a massive 7 x 3" joist, especially over 1.8 metres. Apologies for the mixed metaphors.

Blup

 

[Dereekoo]

2ways to look at this, assuming c16 timber you could shave off 37mm of the total width of the joist so its 38mm wide and this size joist even spaced at 400 centres gives you an allowable span of over 4m or if you took 98mm off the entire depth of the joist this would leave you with a 75 x 122 joist which even spaced at 400 mm would be able to span 2.97m. I think you have more than enough reserve in the joist to notch out what you want.

 

[Dereekoo]

2ways to look at this, assuming c16 timber you could shave off 37mm of the total width of the joist so its 38mm wide and this size joist even spaced at 400 centres gives you an allowable span of over 4m or if you took 98mm off the entire depth of the joist this would leave you with a 75 x 122 joist which even spaced at 400 mm would be able to span 2.97m. I think you have more than enough reserve in the joist to notch out what you want.

Have run the calcs on a joist sizing spreadsheet I have and if I put a 38 x 120 joist size in the deflection and bending moment incurred in the joist with standard floor loading is less than half on both counts of what is actual allowable. In theory it could span 2.2m before deflection limit is exceeded and 2.8m before bending moment limit is exceeded

 

[big-all]

75x220 joists with a 1.8m span - notch away!

100% agree
just checking 1.8 is support under the joists and not just the space between walls above including possible extra loading sitting on the joist underneath??