How we get these numbers

Every range on this page is reproduced exactly as a published cost guide printed it, with the publisher named and the edition and page cited. We derive no midpoint of our own, we never average two publishers into one figure, and where no guide covers a project type we show no range at all.

No adjustment of any kind is applied. There is no regional multiplier and no index-based uplift on this page — an index series we cannot cite by source, edition and licence does not get to move a published number.