Advice on running new bath waste

[Milleniumaire]

Hi, as part of my bathroom refurbishment I was planning to get a stone resin bath and to run the 40mm waste pipe through a number of joists to the side wall of the house where the soil stack is located.

However, having paid a structural engineer to check that my joists could handle such a heavy bath, the answer was no and that I should also avoid running the waste pipe for the bath through the joists as the joists were very close to their "full capacity carrying normal domestic loadings".

The only option left for me is to run the waste pipe with the joists and bring it out of the front of the house. Here's a photo showing some possible routes I can use to run the waste. The pipe exits the house below the upstairs bathroom window.

Bath Waste Routes

• Milleniumaire
• 8 May 2020

1. Run the pipe to the left, then down to the soil pipe below the downstairs toilet using the most direct route 2, down the middle of the wall!

3. To the left again, but run the pipe closer to the edge of the house, then double back to the downstairs toilet soil pipe. Although a longer run, the point of this is to attempt to minimise the impact by placing it near the side wall as there are a couple of drain pipes around the front that are positioned close to wall edges.

4. Run the pipe around the house corner to the existing soil pipe. Although there is a drain pipe between the edge of the side of the house and the soil pipe, this is narrow enough that it wouldn't interfere with the waste pipe. So this run would require two straight lengths and a single 90 degree elbow to reach the soil pipe, where a new boss connection would be used to attach it.

In your experience, which would be the best run?

I like the idea of the shorter run to the soil pipe at the side of the house, but routing round an external corner doesn't feel "normal"! Maybe I'm wrong?

 

[KenGMac]

How about considering setting the bath on to a "Plinth" which is raised above floor level thus allowing you some space to get the pipe out from under the bath to the external wall?

Ken.

 

[Milleniumaire]

How about considering setting the bath on to a "Plinth" which is raised above floor level thus allowing you some space to get the pipe out from under the bath to the external wall?

Ken.

Thanks for the suggestion Ken. We did consider this in the early days of designing the bathroom but felt it wouldn't look correct for the size of the bathroom. I did try to persuade my wife it would make my job easier but it's a none starter for her

We are also having wet UFH installed and although it doesn't go all the way under the bath, it still goes under part of the bath.

 

[Hugh Jaleak]

Length of run needs to be taken into account too, regs only permit a max of 3m on 40mm pipe and 4m of 50mm pipe. Routing round the corner isn't ideal for aesthetic reasons, but nothing says you cant do it, if needs must.

I would use Tees on the corners though as opposed to bends, and fit cleaning eyes in the unused sockets. Tees are longer radius, which will allow for a smoother flow of water.

 

[Milleniumaire]

Length of run needs to be taken into account too, regs only permit a max of 3m on 40mm pipe and 4m of 50mm pipe. Routing round the corner isn't ideal for aesthetic reasons, but nothing says you cant do it, if needs must.

I would use Tees on the corners though as opposed to bends, and fit cleaning eyes in the unused sockets. Tees are longer radius, which will allow for a smoother flow of water.

Thanks Hugh (again ).

Unfortunately, that rules out connecting to the toilet soil pipe as it would be over 7 metres, although the horizontal run is less than 3 metres. I say unfortunately, but I really, really don't want to have to run any pipe on the front of the house, but I'm struggling to find an alternative.

The run around the side of the house to the main soil stack would be 2.6 metres, so it sounds like this would be within regs, but as you say, aesthetically, it doesn't look very good.

 

[Milleniumaire]

I'm now looking to go back to plan A, which was to run the bath waste pipe under the bathroom floor, which unfortunately means drilling holes through joists. Originally, when I didn't know as much as I do now, the following diagram shows what was required, with the shower and bath 40mm waste pipe shown in yellow. The joists are indicated, so for the bath waste, this would require drilling through 5 joists (the last two joists are directly next to each other on the outside wall).

Original Waste Pipe Runs

• Milleniumaire
• 9 May 2020

The original plan also included a stone resin bath and as I mentioned earlier, a structural engineer told me that wasn't possible as it would be too heavy for our existing joists to cope with. So, we are now looking at acrylic baths, which are much lighter.

To comply with building regs and to ensure holes are drilled through the joists in the appropriate place, I've done the following calculations.

Joist size (length, height, thickness): 378cm x 190cm x 90cm (40cm centres)
Maximum hole size for 190cm height joists is 0.25 x 190cm = 47.5cm so okay for 40mm waste pipe.

The following diagram identifies the area in which holes can be drilled i.e. between 0.25 and 0.4 of the spam, from either end.

Alternative Waste Pipe Runs

• Milleniumaire
• 9 May 2020

The revised bath waste run will be under 3m.

I will probably go back to the structural engineer and discuss this with him although he has already said the joists are at their "full capacity carrying normal domestic loadings". I understand how this would affect a heavy bath, but I'm not too sure how it would affect drilling holes in the joists, especially if they are put in the required part of the spam.

I'm also wondering if it is worthwhile buying an additional joist and cutting it into say 60cm lengths and gluing/screwing this to the three central joists at the point in which the bath waste will run through them (shown on above diagram). This should provide some additional support.

Can anyone see any issue with this plan in terms of building regs? Have I missed anything? Is doubling up the joists likely to be worthwhile?

 

[KenGMac]

OK here is an of the wall suggestion?

How about dropping the waste directly down to the ceiling of the floor below? then form a "mock beam" on the ceiling to hide the pipe work?

If needed [and allowed by the "BOSS"] other beams could be formed on the ceiling to achieve ballance?

Ken.

 

[lostinthelight]

Will it matter that the holes through each joist will be getting progressively lower to maintain the correct fall

 

[Nige F]

The run around the side of the house ; aesthetically, it doesn't look very good.

I agree - but for a few £ you could buy a length of black waste pipe and temporarily fix it - a few screws in a horizontal joint and tied up - then literally live with it for a few days . Then decide .Drilling those joists will be a **** job and the inside waste has to have a bend hidden ( as per your drawing ) though you could use 2 x 135 degree bends . An off the wall, or on the wall idea ?

 

[Milleniumaire]

OK here is an of the wall suggestion?

How about dropping the waste directly down to the ceiling of the floor below? then form a "mock beam" on the ceiling to hide the pipe work?

If needed [and allowed by the "BOSS"] other beams could be formed on the ceiling to achieve ballance?

Ken.

Thanks Ken, that's an interesting idea and I've had a discussion with the missus. As it happens our lounge has a steel beam down the centre of the ceiling effectively splitting the ceiling in two, so I know what this would look like.

However, the room below the bathroom is much smaller and so wouldn't allow this, there's also some fancy coving around the edge, which would be difficult to replace if damaged. This idea has made my wife say she would rather have a platform!

I agree - but for a few £ you could buy a length of black waste pipe and temporarily fix it - a few screws in a horizontal joint and tied up - then literally live with it for a few days . Then decide .Drilling those joists will be a **** job and the inside waste has to have a bend hidden ( as per your drawing ) though you could use 2 x 135 degree bends . An off the wall, or on the wall idea ?

Not a bad idea. I was also thinking the pipe could be painted stone coloured, or possibly use white pipe, rather than painting it the same grey/blue as the rest.

 

[Milleniumaire]

Will it matter that the holes through each joist will be getting progressively lower to maintain the correct fall

I'm sure this definitely would be an issue. If I were to drill exactly the centre of each joist I wouldn't get any fall on the waste pipe. I would therefore need to start slightly higher than centre and finish slightly lower than centre.

I'm probably going to run the pipe on the front of the house and around the corner to the soil pipe. This seems to be the simplest solution and hopefully after a while I won't even notice the pipe.