Can I change my design after gaining planning consent?

I intend to start a new build project in March 2020 and expect to extend the property at some point in the future. I would like to construct the footings for this extension at the start of the project – alongside the foundations for the main house. The current plan was approved with a 3m extension (with further permitted development rights taken off) but I would now like to increase the size of the addition to 8m.

Can I legally increase the extension floorplan size without alerting the local authority? Also, when should I notify the council about my plan being a new build?

If you want to depart from the approved plans, ideally, get your permission amended first. In your current situation, if you build foundations for a future extension, the council could take the view you have departed from the permitted scheme.

at said, foundations alone shouldn’t trigger their interest, but it’s not without an element of risk. e legalities, as is often the case with planning, are open to interpretation.

However, if further permitted development rights have been taken off as a planning condition, then adding a larger 8m rear extension would require you to submit a planning application. Unless you’re completely confident that this would be granted, you’d be taking quite a large financial risk by spending more money on any additional foundations.