Runnung bathroom waste under floor, through joists.

Clarifications:

the shower waste isn't an issue because there is already a bath waste which runs under the floor to the soil stack. Joists run across the property so that waste should be between the joists.

The issue is the WHB. At present this is on an internal wall and the waste runs under the bath. To run this under the floor would require crossing several joists. I haven't yet measured the depth of the joists but assume that most are long. There will be some complexity as a chimney was removed during renovation which would originally have supported some of the joists. I assume they are now supported by one of the steels.

At the moment the options seem to be fitting a pump which can then force the waste through a smaller bore of pipe, or re-locating the WHB to the shared wall of the semi-detached house.

The shared wall seems the better option, especially as there is a 100mm+ void behind the plasterboard for sound proofing purposes (we can no longer hear bathroom noises from next door) so the pipework could be concealed within there.

Slightly at a tangent, is it worth considering lifting the floor boards under the shower tray so that it sits more or less flush with the floor?

Cheers

Dave R

In my own bathroom, I covered the floorboards with 1/2" cement boards (cut around the shower tray), an electric heating mat and ceramic tiles. It does significantly reduce the apparent height of the low-level shower tray. However, removing the floor boards would be a step too far - many require to sit on a full bed of mortar, on the boards, to even out the "point" load of someone standing in them.

It depends on your type of tray. Many will require a full bed of mortar to sit on so they are fully supported - so you would need something spanning the gap over the joists.

And in the centre line of the joist, which is tricky if you want to run a 50mm through a few joists, even in the correct 0.25 to 0.4 span, and also have a bit of a fall.

I was vaguely wondering about something thinner than a floorboard (ply, metal, something) which would drop the tray a little but still spread the load.

Cheers

Dave R

On the "resin stone" shower bases I fitted at my last house it was recommended to add some ply over the boards and then to use a mortar, or silicone, bed. I would be wary of reducing the support if you want a "do it once" job. Rather than trying to drop the shower, have you considered raising the rest of the floor?

That's probably worse than just having the shower above the floor, as it would introduce a step at the bathroom door and you only tend to go in and out of the shower once a day, but in and out of the bathroom multiple times.

If it's a fairly big step up into the shower, you can make a platform in front (or a surround) to split the climb into more manageable increments. Or, at least add a grab handle.

So far everyone is assuming the the joist that has to be notched or drilled is not reinforced with something stronger than wood.

Can you buy pre-made steel reinforcements, designed for this particular job?

You can certainly buy stuff that can be adapted, like a steel joist hangar

Possibly only available in the USA (at reasonable cost) but it gives ideas about how to strengthen a joist.

You may get away wide metal straps beneath a notch, perhaps made from plate steel 3/4 mm thick.

Plywood (also notched) bolted to both sides may be sufficient.

Noggins between the joists near a notch or hole may strengthen the area around where the pipe needs to go.

The relevant advice about the above needs to be sought.

That all looks pretty neat. Expensive, though.

Not sure I'd trust 2mm sheet steel on some of those deep notch brackets . . .

One option is to use the strengthening on both sides of a joist.

Yep, that'd help. That said, I'd say even a couple of these look unlikely:

I was referring to the USA made one @ 10 gauge or 0.14 inch.