The location of sewer lines and or existing drains often gets overlooked when plans are drawn up for new structures or alterations.
This may lead to more pressure on the existing drainage network than it can handle which in turn will lead to numerous call-outs for plumbers.
Details of plumbing equipment is often lacking I.e. type of bath or basin, tile and shower rose or door, these are costly items.
The best and only way to avoid disputes later on is to appoint the necessary and qualified plumbers from the beginning of the project. Remember your building contractor is knowledgeable about building work, but not necessarily about plumbing work.