Understood - let me summarise to ensure I’ve got this. If the neighbour gets the permissions approved, commences excavation work (assuming they do not breach the depth of my foundation), then no PWA is required? If they do breach the foundation, then a PWA is required but it’s already too late by then anyway?
Just trying to understand the definitions as it’s fairly clear in the Act that a PWA must be agreed if excavation work is within 3m of the adjacent property.
A PWA is only required if a neighbour dissents from a PWN. So, yes, the situation sometimes arises that works have to be suspended because foundations are not as they were thought to be, and a PWN then needs to be served.
If the builder gets down to a certain level and finds things are not as they thought, then it would be more imperative to fill the trench quickly with the concrete rather than mess about filling in forms and serving notices, and waiting for the 28 day time for a response and then waiting again while appointing up to three surveyors.
I'm no expert and can appreciate you need to be aware of how to prepare for any problems, but it may be worthwhile to just sit down with your neighbour and discuss it over a cup of tea. He/She could allay many of your fears.