Help with pipe layouts

3 Aug 2009
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United Kingdom
Can anyone please comment on my suggested hot water layout?

the combi boiler is to be placed in a cupboard under the stairs so i will be running the pipes to the landing then down to the cupboard. Is it correct to assume that 15mm pipe should be used for of these water pipes?

Also can anyone suggest a soil pipe layout?

any help will be appreciated

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Water pipe layout fine, plus 15mm is fine. Have you checked that boiler in cupboard under stairs is OK with a gas fitter?

Where is an outside wall (N,W, E or S) and which way do the joists run?

Joist run top to bottom of picture and the outside walls are on the right and
on the bottom, the soil pipe shown runs down the outside of the wall on the bottom

The gas fitter is coming next week to look at putting the boiler under the stairs. its a really big cupboard (big enough to stand up in etc.

Is this likely to be an issue? what sort of things need to be taken into considetration to have a boiler under the stairs?


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You don't show a cold mains to the boiler :idea:

My only issues with boilers under stairs is fire proofing. and how you get out in an emergency.
I'm going to get the boiler fitter to run the cold to the boiler so i don't know what size this will be but i guess its 22mm?

if its only a 1 story house do i still need to do fire boarding under the stairs?

in advice with the soil pipe? can i run the main pipe to the toilet and T the bath sink and shower into the main pipe while under the floor boards or do i need to run them individually to the main soil stack?

Boiler under the stairs - you gas fitter will advise, but problems that may occur are:
1/. If an enclosed space, then you can't have coats or anything hanging in there (fire hazard)
2/. If enclosed, is there sufficient room in front of it for servicing the boiler (i.e. between the door and the boiler)?
3/. Is there sufficient room above it for the flue to escape to - this may also require a cage or a plume management kit externally since it may be below 2m
4/. Externally, is there a car port? If so then this may be a problem due to airflow to the boiler inlet.

Not trying to worry you, but I went throught the same process earlier this year.

With regard to the soil pipe, you will possibly be able to run this between the joists and out into the existing soil stack, but make certain there is sufficient room to allow for a fall over the length, plus that you have enough room to bend into the stack, or you core drill out accurately.

With regard to sink, shower and bath wastes - yes, it is possible to join to the new subfloor toilet waste pipe, but I would advise against it due to:
1/. You will need to install antivac or air admittance valves to prevent the seals within the bath/shower/sink being lost and the room becoming pungent.

2/. More importantly - installing the waste pipes will most likely require cutting through the joists, thus weakening them.

If you hire a core drill for a day to cut holes in the brickwork for the soil pipe, you may as well get your money's worth and drill holes for the other waste outlets too, as well as for an extractor fan if there's not one already installed.

Finally, if this a new use for the room then it will involve building regs and planning department etc etc etc..., plus any new wiring should be completed by a part P qualified electrician who can certify the work...etc etc etc

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