Please help - Installing soil pipe over flat roof

[Bewcs]

Hi there,
let me just start by saying I am looking for some advice on doing my first 'big' DIY project of turning a small bedroom into a bathroom, specifically with the toilet.

I want to put the toilet below the window on an external wall which is upstairs and overlooks a flat roof, the extension which is the current bathroom.
I think that the soil pipe will therefore need to go out the wall, drop down, then somehow run over the flat roof about 2.5m length to meet the stack for the existing soil (currently fitted with a vent).

Attached are some pics of the flat roof and wall that I want to put the toilet on.

I am aware that this is not ideal and should not lie flat (like next door!) and 1 plumber has already said he won’t do this part of the job.

I am guessing I can fit a T-shaped connector where the current vent is on the existing soil and then run a single piece of pipe up to wall. What would be the correct/best way to do this to ensure the pipe has the necessary drop (min 6 inches?) and is sufficiently supported?

I’ve thought of constructing a triangle ‘wedge’ shape frame from stud wall timber and thick MDF, then coat it in something weatherproof and sit this on the flat roof fixed in place with some kind of adhesive. The pipe can then sit on this all the way to the wall and be fixed in place with regular pipe brackets.

I’ve also thought of using something as ‘feet’ to support the pipe at intervals of half a meter or a meter (someone mentioned DuraFoot, maybe something like that).

Are either of these viable options?

Are there better ways I’m missing?

My ability levels are amateur for sure, but I can enlist several family members who have fitted bathrooms before to help.
Sorry for the long post but if anyone can suggest solutions and working order to do things in I’d really appreciate it!

 

[ShaunCorbs]

better off to get a set of goundworkers in to install a new 4" connection where the down-spout is right of the outside door

and then run a new stack pipe like next door have

but both will require building control approval i dont think yours will pass

 

[Pickwickpick]

If you just run it along the flat roof you will not have the required fall (1:40 to 1:110), which means that a) you will get blockages b) you won't get the job signed off. Because you're setting up a bathroom in a room that wasn't originally designed as one, you're going to need building regs sign off, if you don't do this you could have expensive problems if you try and sell your house in the future.

Is the toilet going on the wall with the window or the wall with the gutter downpipe on it?

 

[gingalig]

You're you going to need approval for the new bathroom anyway if you're fitting a bath due to the extra weight involved and the floor structures ability to cope. Adding pipework Into external groundwork as Shaun mentioned, seems the way forward this tagged onto approval for your floor and ventilation requirements would be negligible cost wise.

 

[Chalked]

Hi
You have a gulley in pic 2 that takes the waste from kitchen. Get that dug out and replace it with a vertical soil pipe.
Will give more options of layout in the new bathroom and better fall.

 

[ShaunCorbs]

If you just run it along the flat roof you will not have the required fall (1:40 to 1:110), which means that a) you will get blockages b) you won't get the job signed off. Because you're setting up a bathroom in a room that wasn't originally designed as one, you're going to need building regs sign off, if you don't do this you could have expensive problems if you try and sell your house in the future.

Is the toilet going on the wall with the window or the wall with the gutter downpipe on it?

eg 1m 15mm fall / drop

so a full length of soil pipe eg 3m needs around 45mm of drop

thats what i normally work on

 

[Bewcs]

If you just run it along the flat roof you will not have the required fall (1:40 to 1:110), which means that a) you will get blockages b) you won't get the job signed off. Because you're setting up a bathroom in a room that wasn't originally designed as one, you're going to need building regs sign off, if you don't do this you could have expensive problems if you try and sell your house in the future.

Is the toilet going on the wall with the window or the wall with the gutter downpipe on it?

Thanks for getting back to me. I know the pipe can't lie flat which is why I thought of the 2 options mentioned, build a wedge that is angled at 1 end to create a slope for fall, or use legs to support the pipe at a gradient. Toilet would be on the wall with the window.

 

[Bewcs]

You're you going to need approval for the new bathroom anyway if you're fitting a bath due to the extra weight involved and the floor structures ability to cope. Adding pipework Into external groundwork as Shaun mentioned, seems the way forward this tagged onto approval for your floor and ventilation requirements would be negligible cost wise.

Hi, thanks for the help.
I know building regs will need to come and inspect it once it's in (that's what they told me).
No bath going in, but a shower.
Is groundwork inexpensive?
I thought it would be quite pricey since they will need to dig through concrete under the paving slabs to change the gully.

 

[Pickwickpick]

Thanks for getting back to me. I know the pipe can't lie flat which is why I thought of the 2 options mentioned, build a wedge that is angled at 1 end to create a slope for fall, or use legs to support the pipe at a gradient. Toilet would be on the wall with the window.

Sorry missed that bit, head's a tad fuzzy today! I can't see building regs signing off on either of those. Also you are dealing with a flat roof, your wedge or leg system is increasing the chances of it leaking. If you;re going to the effort to set up a new bathroom, cutting corners on the soil stack is a real false economy imo. You want to run a new stack down the side of the house as @ShaunCorbs recommended

 

[Pickwickpick]

Hi, thanks for the help.
I know building regs will need to come and inspect it once it's in (that's what they told me).
No bath going in, but a shower.
Is groundwork inexpensive?
I thought it would be quite pricey since they will need to dig through concrete under the paving slabs to change the gully.

Get some quotes done and offer to do the prep work (i.e. digging up slabs/breaking any concrete, digging trenches...) and to make good yourself, so they just need to lay the pipes.

 

[ShaunCorbs]

it maybe more but its the best option

 

[Chuck]

Converting a bedroom into a bathroom is likely to reduce the value of the property. Have you sought the opinion of a valuer?

1 plumber has already said he won’t do this part of the job.

That's your first clue that it's a bad idea.

I’ve thought of constructing a triangle ‘wedge’ shape frame from stud wall timber and thick MDF, then coat it in something weatherproof and sit this on the flat roof fixed in place with some kind of adhesive.

You have got to be kidding. That's such a bad idea it's not even wrong.

 

[Bewcs]

Converting a bedroom into a bathroom is likely to reduce the value of the property. Have you sought the opinion of a valuer?

Cheers for your input.
It used to be a bathroom before, but the last owner changed it into a mini bedroom for one of her kids - but it's hardly really fit for that purpose, it's off 1 of the actual bedrooms so you have to go through a bedroom to a bedroom.
In this case a bathroom will add value.

Hmm... doesn't sound like the shortest route the the existing soil is a very popular one!

 

[Riley]

Where’d the pipework run before then??

 

[MOSSEP]

If you must do it the way that you suggest, I would support the pipe using some uni strut feet, some M10 threaded rod and then 110mm pipe rings. You can cut the rod at what ever lengths you need to get the height adjustment required.

Cable Tray and Pipework Support Foot Flexi-Foot - 400mm Strut | Roofing Superstore®

 

[Bewcs]

If you must do it the way that you suggest, I would support the pipe using some uni strut feet, some M10 threaded rod and then 110mm pipe rings. You can cut the rod at what ever lengths you need to get the height adjustment required.

Cable Tray and Pipework Support Foot Flexi-Foot - 400mm Strut | Roofing Superstore®

Wow, that's super helpful and would do the job perfectly! Thank you!

Have you used these before and would they pass building regs?
Over a 2.5m length how many supports do you think would be suitable?

 

[Riley]

I think enlist your local building inspector before you do anything as they will advise

 

[gmartine]

Wow, that's super helpful and would do the job perfectly! Thank you!

Have you used these before and would they pass building regs?
Over a 2.5m length how many supports do you think would be suitable?

Suitable for supporting small diameter pipework only.

 

[MOSSEP]

Wow, that's super helpful and would do the job perfectly! Thank you!

Have you used these before and would they pass building regs?
Over a 2.5m length how many supports do you think would be suitable?

I would put one within 300m of each bend or branch and then spaced at 800mm maximum between supports. I have used them loads, they will be fine.

Not sure what building control would say, Id imagine there only concern will be adequate pipe fall and ventilation of the stack.

 

[MOSSEP]

Try this site for other options, I get a lot of strut and supports from here

Strut Mounts

 

[ShaunCorbs]

Suitable for supporting small diameter pipework only.

Waste pipe will be fine that comment is more towards steel pipework

 

[Bewcs]

A bit of good news update.
Emailed building control in our area with a link to the strut mount page as an example, the surveyor said they can't see an issue with that as long as there is sufficient fall and ventilation

 

[gmartine]

Waste pipe will be fine that comment is more towards steel pipework

Fair enough, still gonna look like a pig though.

 

[ShaunCorbs]

Fair enough, still gonna look like a pig though.

And vent won't work at the bottom / where it is now as the op suggests

 

[Bewcs]

And vent won't work at the bottom / where it is now as the op suggests

Sorry, that'll be my ignorance here, but can the ventilation not sit as it does now but with a T joint below it to connect up to the new soil coming in?

 

[Riley]

It will have to vent higher than the highest outlet

 

[Pickwickpick]

Sorry, that'll be my ignorance here, but can the ventilation not sit as it does now but with a T joint below it to connect up to the new soil coming in?

No it won't work, you need either a vent outside that goes 300mm above the eves or you'd need an air admittance valve (AAV) in the new bathroom. AAV are not a reliable and I don't like them and personally would not fit them and would want the soil stack done 'properly'.

 

[ShaunCorbs]

Sorry, that'll be my ignorance here, but can the ventilation not sit as it does now but with a T joint below it to connect up to the new soil coming in?

No as poo would come out of the vent

 

[ShaunCorbs]

No it won't work, you need either a vent outside that goes 300mm above the eves or you'd need an air admittance valve (AAV) in the new bathroom. AAV are not a reliable and I don't like them and personally would not fit them and would want the soil stack done 'properly'.

Too close to the window for an aav I would say

 

[Pickwickpick]

Too close to the window for an aav I would say

Even if its to the left of the window? Thought the 3m rule didn't apply to AAV?

 

[ShaunCorbs]

Even if its to the left of the window? Thought the 3m rule didn't apply to AAV?

Think it's reduced to 1m or 0.5m

 

[Pickwickpick]

Think it's reduced to 1m or 0.5m

Just been checking the Durgo & Floplast AAV technical brochure and I can't find any mention of a minimum distance to windows. The only reference in there about installation within a habitable space (i.e. not in the loft) is about sound nuisance and that adequate sound insulation should be used.

Having a look at the pics again, looks like it should be possible to run the stack up into the loft space above the bathroom pretty easily and then install an AAV in there which would make it a moot point and would be tidier.

 

[Bewcs]

So with an AAV the options are buy an external one and run the soil stack up the outside wall left of the window, or extend the soil stack up into the loft indoors and box it in within the room?

 

[ShaunCorbs]

Run it external up the side and vent it past the gutter

 

[NickH]

This is so ridiculous. Why on earth would anyone try to run a soil pipe across that roof with all the associated problems of fixing it and getting a fall, into that existing soil vent, with all the associated problems of removing the vent and causing other problems with the waste pipe work in that bathroom and then mess around with a Durga in or out of the loft.
For goodness sake just do it properly, dig the gully up, replace it with a soil stack, branch off for the new bathroom, take a vent pipe up and around the guttering and then reconnect the existing kitchen wastes into the stack with boss's.
It's so easy to do I can't understand why you would attempt to do anything else.
That's just my opinion of course.