Shower or basin drain across joists? (bathroom planning)
Discussion
Hello peeps,
We're planning the layout for our new bathroom and I have a query about whether we'll be able to run a drain pipe through joists under the chipboard floor.
Imagine a square room, with the main drain riser in one corner and either a shower or basin in the opposite corner. The drain pipe from the shower or basin therefore needs to run parallel to the joists then (if possible) across the joists. It'd mean going through about 4 joists.
All the other drains can be parallel to the joists, toilet included, but we can't avoid one running across them. Is this possible or advisable?
If not possible with one drain pipe, could you have a sort of manifold and divide the drain up into several smaller pipes?
Ta
Ruari
We're planning the layout for our new bathroom and I have a query about whether we'll be able to run a drain pipe through joists under the chipboard floor.
Imagine a square room, with the main drain riser in one corner and either a shower or basin in the opposite corner. The drain pipe from the shower or basin therefore needs to run parallel to the joists then (if possible) across the joists. It'd mean going through about 4 joists.
All the other drains can be parallel to the joists, toilet included, but we can't avoid one running across them. Is this possible or advisable?
If not possible with one drain pipe, could you have a sort of manifold and divide the drain up into several smaller pipes?
Ta
Ruari
Are you crazy man?
From what I have read, cutting joists is a major 'no no'.
You will weaken them and place their integrity in jeopardy.
The joist could be strengthened by a metal plate extending either side of the cut and bolted through in plenty of places, but I doubt hat this would be acceptable by a Structural Engineer.
Anyway, hurry up mate, get the job done and report back. I aim to do the exact same thing within a few months.
At the moment my shower cubicle is too high and I want to change it to a walk in type flush to the floor.
Good luck!
From what I have read, cutting joists is a major 'no no'.
You will weaken them and place their integrity in jeopardy.
The joist could be strengthened by a metal plate extending either side of the cut and bolted through in plenty of places, but I doubt hat this would be acceptable by a Structural Engineer.
Anyway, hurry up mate, get the job done and report back. I aim to do the exact same thing within a few months.
At the moment my shower cubicle is too high and I want to change it to a walk in type flush to the floor.
Good luck!
Hi
I had the exact same problem when doing our bathroom last year, and all of the research I found online said that you couldn't/shouldn't cut or drill joists to the diameter of standard waste pipe (35mm I think without going to check).
In the end I lifted the shower tray up on a small platform (I didn't really want to have to do this as it was a slim line tray and would lose the effect) and ran the waste effectively on the surface, around a 90 deg corner to the sink where it could drop through the floor and then run along the joist. I had the advantage however as the wall was being moved I could box in the pipe in back of a built in wardrobe in the next door bedroom, avoiding it in the bathroom.
Once the platform of the shower was tiled the same as the walls, you really wouldn't think it wasn't meant to be like that.
Not sure if this helps at all!
I had the exact same problem when doing our bathroom last year, and all of the research I found online said that you couldn't/shouldn't cut or drill joists to the diameter of standard waste pipe (35mm I think without going to check).
In the end I lifted the shower tray up on a small platform (I didn't really want to have to do this as it was a slim line tray and would lose the effect) and ran the waste effectively on the surface, around a 90 deg corner to the sink where it could drop through the floor and then run along the joist. I had the advantage however as the wall was being moved I could box in the pipe in back of a built in wardrobe in the next door bedroom, avoiding it in the bathroom.
Once the platform of the shower was tiled the same as the walls, you really wouldn't think it wasn't meant to be like that.
Not sure if this helps at all!
Basically, no you won't be able to notch the joists.
Max depth of notches = Joist depth / 8
Max size of holes through centre-line of joist = Joist depth / 4
If joist depth > 250mm then assume D = 250mm
So you can't notch deep enough for a waste pipe, let alone increase the notch sizes to allow for the necessary fall.
You'll have to run the pipework above floor level and then box it in.
As for constructing some kind of manifold to spread over multiple smaller pipes - just no
Max depth of notches = Joist depth / 8
Max size of holes through centre-line of joist = Joist depth / 4
If joist depth > 250mm then assume D = 250mm
So you can't notch deep enough for a waste pipe, let alone increase the notch sizes to allow for the necessary fall.
You'll have to run the pipework above floor level and then box it in.
As for constructing some kind of manifold to spread over multiple smaller pipes - just no
If you've exhausted all other possibilities, then possibly consider using a Saniflow waste pump which will mean your waste pipe size out of the unit only needs to be 22mm, which can be notched.
Mechanical pumps really are the last option to choose when all other options have been eliminated as not possible. I wouldn't install one by choice, even in a little used room.
Mechanical pumps really are the last option to choose when all other options have been eliminated as not possible. I wouldn't install one by choice, even in a little used room.
It's not easy to notch mascerator pipes either. The manufacturers have fairly tight parameters in which pipes can be run, but as far as I can remember they ALWAYS need a fall which would quickly foil any attempt to run through any number of joists. The way they are intended to be used is to pump UP first...then fall to drain.
post up a plan.
considered all the other options, whats below the bathroom? possible to run straight down, or along joist then down or along below ceiling line??
Considered a raised floor, or partly raised floor running side to side to resemble a feature? possible to include sunken or semi sunken bath?
considered all the other options, whats below the bathroom? possible to run straight down, or along joist then down or along below ceiling line??
Considered a raised floor, or partly raised floor running side to side to resemble a feature? possible to include sunken or semi sunken bath?
Thanks for the various info and suggestions.
We did manage to come up with a new arrangement for the bathroom which gets rid of the need to go across joists, except for one small bit which we can box in without ruining the look we want.
However, we had a guy round from a bathroom fitting company today (through the Bathstore) and he told my wife that it's common practice to notch the joists for the drain then reinforce with steel plate(s). I didn't meet him but it he was professional in his approach and confident in what he was talking about.
I must admit I'm not overly keen on that idea, but has anyone got any comments?
I'm inclined to stick with our revised layout now anyway
Ruari
We did manage to come up with a new arrangement for the bathroom which gets rid of the need to go across joists, except for one small bit which we can box in without ruining the look we want.
However, we had a guy round from a bathroom fitting company today (through the Bathstore) and he told my wife that it's common practice to notch the joists for the drain then reinforce with steel plate(s). I didn't meet him but it he was professional in his approach and confident in what he was talking about.
I must admit I'm not overly keen on that idea, but has anyone got any comments?
I'm inclined to stick with our revised layout now anyway
Ruari
As I understand it the guidline for holes is joist height divided by 4 as a maximum hole size and in the centre of the joist vertical, not gradually drilled from high to low to give a drop? If thats correct, depending on joist depth and the length of run across the joists could you not drill holes out to the maximum allowed (i.e. 50mm on a 200mm joist), then put 35mm pipe though which will give you a ~15mm drop along it's length supporting it at each joist so it didnt sag, as long as you have space to feed the pipe in. Seems odd that this would satisfy regulations but 35mm holes drilled within the same footprint slightly offset to give the same drop wouldnt but hey ho.
LocoBlade said:
could you not drill holes out to the maximum allowed (i.e. 50mm on a 200mm joist), then put 35mm pipe though which will give you a ~15mm drop along it's length supporting it at each joist so it didnt sag, as long as you have space to feed the pipe in.
I wondered about something like that, although we'd also need to make a hole in the wall through to one of the adjacent bedrooms to get the pipe in Unless you can get some sort of flexible drain pipe???, or use a series of short bits with joints in between the joists! 
Ruari
Simpo Two said:
Plastic pipe bends a bit.
But I'd use 36mm holes not 50mm!
As for regulations, who is ever going to know?
I only said 50mm holes if there was a requirement to demonstrate compliance with current building regs, if you drilled 36mm holes you'd have to offset them vertically as you go across the beams in order to get a drop, which silly though it is, doesn't appear to meet building control requirements. But I'd use 36mm holes not 50mm!
As for regulations, who is ever going to know?
If there's no official looking over your shoulder though I agree, a smaller offset hole within the same boundaries is going to weaken the wood less than a larger centrally drilled hole.
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