Topic starter
We have a freestanding bathtub that's raised up a little so the drain pipe runs above the floorboards. It then runs along 2 walls to the soil stack. Soil stack runs inside the house not outside.
The house is a barn conversion so timber framed and use to an open car port with the first floor a flat. The previous owners converted it into a house and did a lot of work so it does seem odd they left the bath raised up like this as it's really not practical to use. But maybe there is a reason for this?
We would like to remove the bath and have a shower installed. My instinct was to raise the shower and use the existing drain pipe. We had a first quote and they said they can relocate the pipe under the floor.
Does anyone know if there might be a reason why we shouldn't have the pipe under the floor?
Posted : 13/04/2025 4:53 pm
<Tries to think of feather puns, can't manage it>
What you need is sufficient fall on the pipe to drain the shower tray/bath properly - that's why the bath is raised with the current setup. If the plumber says he can run it under the floorboards and achieve sufficient fall, that's a far preferable outcome aesthetically and practically, unless you like looking at plastic pipe or have a long, boxed in run. Plinth shower trays (on legs) can be OK, but you'll have less choice and they are more likely to flex and feel a bit shit.
What's under the floor? Chances are someone installed the bath flush, fall was insufficient, bath was raised as a bodge. If it's a long pipe run you'll need close to 20mm fall per metre. I think a wider diameter pipe would be required if the run was over a certain length.
Posted : 13/04/2025 5:06 pm
fazzini reacted
<Tries to think of feather puns, can't manage it>
Yeah, I’m trying to make something work with millinery or milliner, just not getting there, sadly. 🤷🏼♂️
Posted : 13/04/2025 5:10 pm
<Tries to think of feather puns, can't manage it>
That must make you feel down.
Posted : 13/04/2025 5:12 pm
Was trying something based on 'water off a duck's back', but couldn't make it work. Wordsmiths of STW, assemble!
Posted : 13/04/2025 5:13 pm
Joist direction?
In combination with holes and keeping to safe limits, maybe?
Posted : 13/04/2025 7:20 pm
Topic starter
The pipe would have to pass through 8 joists.
Posted : 13/04/2025 10:34 pm
Sounds very iffy then with that number of 40+ mm holes unless the joists are massive. Did the plumber know that when he was quoting to do it that way? Is there an external wall you could use for the run? , EDIT: internal stack as you mentioned. What's the room underneath like - any chance of boxing in a run along the ceiling there?
Posted : 13/04/2025 11:47 pm
Well you're not making 40mm holes in joists. 8 of them, in line with fall, not without seriously weakening the joists. So it's not possible surely?
Posted : 13/04/2025 11:48 pm
If you're in any doubt about holes in joists, guidance is here https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists
Ask the plumber to show their working; the slightest misalignment in hole drilling will mean an even larger hole if the fall is to be maintained.
A domestic lifting station (like a macerator, but without the WC connection) will reduce pipe diameter and might help your situation
Posted : 14/04/2025 7:41 am
If it ain't broke... .
I know Italian style walk in showers are fashionable but my advice is don't, it'll leak. If you really want a shower then a quality ceramic base on a plinth with an arm size access hole and with exposed waste plumbing with access for cleaning at bends will serve you well. Box it in either where it is or under the floor as martinhutch suggests, but a walk-in and running through joists will mean a demolition job if there's a leak.
I'm working on one at the moment. The big beam you can see supports the joists which leaves a clean run for the plumbing. The walls are the next step then the floor boards which will be removable for access to the plumbing.
Posted : 14/04/2025 8:14 am
If you're in any doubt about holes in joists, guidance is here https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists
Ask the plumber to show their working; the slightest misalignment in hole drilling will mean an even larger hole if the fall is to be maintained.
A domestic lifting station (like a macerator, but without the WC connection) will reduce pipe diameter and might help your situation
Wow. So in the right place a standard 2x10 floor joist can take a 40mm pipe through it. Plumber is going to have to use lots of short lengths and joins to get the pipe in, but it's doable.
Posted : 15/04/2025 2:58 pm
Except he has to pretty much drill on the centreline of every joist and that will screw up the fall. Also, I might put up with one, or maybe two drilled joists, but eight in a row would worry the hell out of me. Reckon you'd feel the floor flexing!
Posted : 16/04/2025 4:54 pm
You could consider paying an engineer to do calculations. There's a good chance that holes could be positioned to suit the fall. The joists are currently supporting a bath, and full bath is much heavier than a shower, plus the joist depth is usually standard across the whole floor and may be more than necessary for the span. You need to look at where any holes would be needed relative to where the joists are supported, which may not be where the bathroom walls are - where are the loadbearing walls underneath? You may be able to plan the route of the pipe to go through less crucial parts of the joists.
A joist is stressed in shear near the supports, so needs the full depth without notches or holes. As you go into the span the shear force reduces and notches are possible. The further you go towards the centre of the span the more the joist is working in bending, so the stress is concentrated in the top and bottom, and holes through the mid-height are possible. If not fully loaded, maybe a bit up or down from the middle will be acceptable.
I'm not saying it will work, but it may be worth getting an engineer to look at it. I'm retired and uninsured so I'm not offering.
Posted : 17/04/2025 8:34 am
As an engineer you'll know about the properties of wood and its high resistance to shear across the grain and that near the supports the shear resistance really isn't an issue. However the elastic module means it's bendy stuff and it's not very strong in tension so reducing the section in the middle isn't a good idea. I'd happily reduce a joist to half thickness at the support but not in the middle.
Posted : 17/04/2025 9:11 am
