My neighbour will be starting work on a side return extension shortly and I am concerned about the water drainage and the build over of any pipe work. I understand that this is a separate agreement and part of the building control works. Is there anyway we can request/caveat that we want to see approved documentation for these works?
Drainage is covered by the Building Regulations and will therefore be checked and signed off by the Building Inspector. If they are within building within 3 metres of a public sewer a ‘build over agreement‘ will be required from the local water authority and they will undertake their own checks.
The party wall surveyor(s) can only consider how your below ground drainage might be affected by the notified works which, in practical terms, will be the excavation. This would take 2 forms, either directly if a shared drain is being altered or in the longer term by damage as a result of ground movement.
The surveyors should limit the amount of time that a shared drain should be temporarily bunged and ensure that there is sufficient capacity in the pipework for this not to become an issue.
Surveyors will often include a requirement in the award for the building owner to arrange a pay for a CCTV scan of the adjacent below ground drainage before and after the works. If there is a real risk of ground movement such would be a sensible precaution that protects both owners.