We have planning permission to building an extension. There is a mains sewer running through our garden which we need to relocate. We have plans to move it so that it runs centrally between us and next door (1.5m from each property) and our architect has had these plans approved by the water company. BUT, when we gave our neighbours a party wall (excavation) letter it turns out there is a problem. They bought their house 3 years ago with an indemnity in place. It turns out that their single storey extension, which runs along our boundary, was built 20 years ago and there is no record of planning permission or building regs so no record of structure/foundations. They are therefore concerned that building work could damage their property. We have adhered to all stipulations - the problem is with their property. Are we liable for appointing an independent surveyor in this instance, or are they. Can they, in fact, stop us building when it's their property that is the issue?
Your neighbours cannot stop you carry out your proposed works, but are fully within their rights to ensure their property is protected. They can appoint a survey under S10 of the Party Wall etc Act 1996, the foees for whom normally fall with the building owner.
The act takes into account all possible queries so it is important to appoint someone familiar with party wall proceedures. It would be prudent to make a condition within the Party Wall Award to have a tiral hole excavated so that the extent and arrangement fo the Adjoining Owners foundations can be ascertained prior to works being carried out.
Thanks for your advice - it's good to know someone, somewhere is listening!! We've spoken to a structural engineer and his advice (having dug a hole himself to check footings) is that the trench should be shored up with steel sheeting prior to excavation. He reckons this will safegaud next door's extension and actually make it stronger! Hoping to avoid appointing official party and therefore avoid costs and delays ...
One word of caution regarding your final sentence. If you are excavating to an assumed lower level than your Adjoining Owners foundations and within 3m, you must, by law (The Party Wall etc Act 1996 - S6) serve notice on your Adjoining Owner informing them of the work. If they agree you do not need to follow the full proceedures of the act. If they do not then you will have no choice but to follow correct proceedures.
If they agree, i would suggest that you agree with your neighbour to take lots of photos of the inside and out of their property and then both sign the back. This will record the condition should a future dispute arise.
The danger of not doing anything is your neighbour saying to you "a crack has appeared in my ....., it wasn't there before you started work" All you have to do is prove it one way or the other which is likely to be impossible.