Permitted Development and Drains

[bennettp23]

Morning All,

I'm looking for a bit of advice from people who know much more than me please .

We are wanting to extend the house. Single story to the rear. I've drawn it out as per the picture.

Originally we were also considering a 2 meter width single story side extension too but with the boundary wall being 3m from the side of the house and a public drain running down the side of the house, we think that is probably just too much to deal with but I've included in the questions below.

We have a large garden so no chance of exceeding the 50% curtilage rule. There is an inspection chamber under the proposed extension that takes in the toilet soil pipe and kitchen drains. I've included a picture of the inspection chamber. The soil pipe is internal to the building.


So my questions:

1. Am I right in thinking that both the rear and side extensions would be permitted developments?
2. As the proposal is essentially rectangle boxes I'm thinking I can use a structural engineer to design and draw the plans?
   
3. I would need a build over agreement from United Utilities (even if it was just for the rear extension we went for) as once the neighbours drain joins ours in our property it is then public and within 3m of the new building works?
4. What do we do with the drains and inspection chamber that are under the proposed rear extension - this part worries me?? Would it be easier to 'pop' the soil pipe out and into the new extension ceiling (or down side of house) to run down the side of the house so it isn't under the extension? Or move inspection chamber to the side of the extension and run it under (as per picture with my squiggle on it)?
5. Is the side extension very troublesome and expensive due to the public drain running all the way down it?

Sorry for all the questions - I hope they make sense.

Thanks!