Have you checked what the site will allow?

Before taste gets a say, the plot decides what is buildable. Boundaries, drains, trees, services and access set the outer limits, and every one of them is discoverable before you pay for a design.

The cheapest survey is always cheaper than the redesign it prevents.

The title register and title plan tell you where your ownership ends and whether anything is registered against the property — rights of way, covenants restricting extensions, shared access. They cost a few pounds and take minutes to obtain.

A drainage asset plan from the water authority shows public sewers and shared laterals. If a sewer crosses your footprint, you are into a build-over agreement, and possibly a diversion.

Trees with preservation orders, ground conditions, an old shared drain running diagonally across the garden, an electricity or gas service crossing where the foundations want to be — none of these are visible on a sunny site visit.

Foundations were dug on a Kent extension before anyone requested an asset plan. A shared lateral drain ran diagonally under the new footprint. Redesigned foundations, a build-over agreement obtained retrospectively, and three weeks lost — all for a document that could have been requested at the very beginning.

How does a nine-tonne load of materials reach the back of the house? Is there anywhere to put a skip, a welfare unit, a spoil heap? Restricted access can add meaningfully to labour because everything is barrowed rather than delivered.

Builders price what they can see. If access is difficult, say so in the tender pack — otherwise you will hear about it as a variation.

Physically pace the plot against the title plan. Fences move over decades, and the line you have always assumed is yours may sit half a metre off. Discovering that at excavation stage turns a survey question into a neighbour dispute.