Waste pipe problems in new build

[Zoe100]

Hi could anyone give advice please ? I went to look at a new build for sale they are apartments/ one house on top of another all properties will be privately owned by individual buyers, a guy on-site pointed out that the plumbing is wrong on the properties as a perspective buyer I’d like to know if it’s legal ? The top properties waste/ soil stack runs into the downstairs properties waste pipes, so basically all your waste is going through the downstairs flats pipes, yet on the show home the soil stack/ waste pipes from each property are separate, the upstairs goes out through the wall not into someone else’s pipe. Surly having someone’s wastes going into your pipes isn’t legal when the properties are privately owned, surly it will cause huge problems if there’s blockages ect ? Are there pluming regulations for this ?
TIA

 

[ShaunCorbs]

Nope quite common shared stack etc

 

[Zoe100]

Nope quite common shared stack etc

It’s a new build 2 completely separate houses it just happens that one is on top of the other

 

[ShaunCorbs]

Apartment