Historic England’s Conservation Principles defines restoration as returning a building to “a known earlier state, on the basis of compelling evidence, without conjecture”. A number of criteria are set out which normally make restoration acceptable.

These criteria include:

1. Weighing up the effect of change restoration work would bring to the heritage values of the building.

2. Compelling evidence for the restoration work.

3. The form of the building as it currently exists is not the result of a historically significant event.

4. The proposed work respects previous forms of the place.

5. The maintenance implications of the proposed restoration are considered to be sustainable.

6. The distinction between restoration and repair can sometimes become blurred when architectural details and or decorative elements that are important to the character and appearance of a building become eroded or damaged.

7. Often a programme of repair provides an opportunity for the reinstatement of missing non-structural elements, provided sufficient evidence exists for an accurate replacement, no loss of historic fabric occurs and the necessary consents are obtained in advance.

8. In some circumstances, restoration may provide conservation benefits that cannot be achieved through repair alone.For example, restoring the roof on a roofless building may be the most cost effective way of conserving valuable internal fabric, such as wall paintings or plasterwork. It may also help to make the building physically and economically sustainable in the long term.