Soil pipe inside or outside

[ifti12]

Hi,

Need some advice on the soil pipe inside or outside, I have searched on google and read couple of forums but don't find the right or wrong answer of soil pipe being inside or outside the property.

We are adding two rooms on the side of the house and one loft into dormer conversion. Please see in the attached image the two bathrooms on the side of the property will go directly into main sewerage.

My question is regarding the highlighted circled image with two options.
1) OPTION 1: Soil pipe for main first floor bath and dormer ensuite to pass through inside the property, the advantage I can see is less travel hence less chances of problems but I am thinking in the long term if there would be a problem, my floor would be concrete, underfloor heating so it would be a complete mess if we have to diagnoses something inside the property plus odour/smell is also what might causes a problem. (The house was built around 1970s and this is how the current soil pipe was, it was boxed from first floor bathroom to kitchen below but now we have added another bathroom in dormer just above the first floor bathroom)

2) OPTION 2, Soil pipe all the way outside the property to the main sewerage as shown in the image. Advantage less pain in case of problems, no odour because less soil pipe inside the property. Long travel of pipe which may or may not be a problem. My house is on slightly sloppy ground all the way from front to back but I think the slope will be same even if we go inside the house.

Can you please comment on both options or do you have any better option than these ? Builder is towards OPTION 1 because less digging and less labour.

Thanks
ifti

 

[Bonni]

Option 2, I always run soil pipes around the property.

Soil pipes comes under Document H in the building regs I would study that.

Also, If alter the 4" soil pipe to a toilet, technically, you should apply for building regs. How do I know? Building regs guy came out to look at a steel lintel we installed and he was more bothered that the location of the toilet had been change, the pipe had been extended. So he rang the office and got it added to the notice for the steel so it didn't cost any extra. We thought that was bizarre but I suppose it's to follow Document H.

https://www.gov.uk/government/publications/drainage-and-waste-disposal-approved-document-h

 

[Hugh Jaleak]

Nothing wrong with running drainage under a building provided it is correctly installed, and is a straight run from the base of the stack to the outside of the building. Laid properly, it should never cause an issue, and in the event it did block, could be accessed from outside to be cleared.

Looking at your plans, I'd run the drainage from the stack serving the first floor under the house, going externally means a longer run and several changes of direction, internally is a straight run to outside. The ground floor WC can run externally, ensure there is a chamber fitted at the change of direction.