Heritage Planning Glossary: Significance, Setting, Curtilage
Heritage planning uses a tight vocabulary of technical terms that the NPPF treats as terms of art. The five most consequential are significance, setting, curtilage, substantial harm and less-than-substantial harm. Each is defined below with the underlying authority.
On 17 August 2026 the Government published a revised National Planning Policy Framework, which is a material consideration in decisions from that date. It restructured the historic environment chapter into thematic policies (HE1 to HE9) and no longer uses the numbered paragraph citations in the harm entries below, and the term 'less than substantial harm'.
Under the 2026 Framework, applicants assess the significance of the assets affected and the likely effect of the proposal under Policy HE5, on a five-point scale: positive effect, no effect, harm, substantial harm, or total loss. The two-tier ‘substantial / less than substantial harm’ test has been removed and the phrase ‘less than substantial harm’ no longer appears. Harm to a designated heritage asset is now weighed under Policy HE6, where any harm is a matter of considerable importance and weight; non-designated assets are dealt with under Policy HE7. The explanation below describes the framework that applied until 16 August 2026 and is being updated. Always check the current NPPF at gov.uk.
Significance
NPPF glossary: 'The value of a heritage asset to this and future generations because of its heritage interest. The interest may be archaeological, architectural, artistic or historic. Significance derives not only from a heritage asset's physical presence, but also from its setting.' Subdivided by Historic England 2008 Conservation Principles into evidential, historical, aesthetic and communal values.
Setting
NPPF glossary: 'The surroundings in which a heritage asset is experienced. Its extent is not fixed and may change as the asset and its surroundings evolve.' Operationalised by GPA 3. Includes views to, views from, kinetic experience, historic associations, intervisibility.
Curtilage
Not defined in NPPF; the test is in case law. Debenhams plc v Westminster CC [1987] AC 396 (HL) sets the leading authority. Curtilage listing under LBCAA 1990 s.1(5) protects pre-1948 structures within the curtilage that are physically attached to the listed building or form part of the land.
Substantial harm
The higher-harm threshold. Bedford BC v SoSCLG [2013] EWHC 2847 (Admin): the threshold is reached where the proposal would 'vitiate altogether or very much reduce' the significance. A high bar; reserved for demolition, major alteration removing principal heritage interest, or setting impacts that fundamentally undermine appreciation. Under the 2026 NPPF, harm to a designated heritage asset (including substantial harm and total loss) is assessed under Policy HE6; the pre-2026 numbered paragraph is superseded.
Less-than-substantial harm
A pre-2026 term of art for the spectrum below the substantial-harm threshold, weighed against public benefits, carrying 'considerable importance and weight' on the planning balance per Forge Field Society [2014] EWCA Civ 137. The phrase does not appear in the NPPF published 17 August 2026, which instead grades the effect of a proposal on a five-point scale (positive effect, no effect, harm, substantial harm, total loss) under Policy HE5. The special-regard duty under LBCAA 1990 s.66 is unchanged.
Designated heritage asset
Listed buildings, scheduled monuments, protected wreck sites, registered parks and gardens, registered battlefields, conservation areas, World Heritage Sites.
Non-designated heritage asset
Buildings, monuments, sites and landscapes identified as having a degree of heritage significance meriting consideration in planning decisions, but not formally designated. Includes locally-listed buildings and archaeologically-significant sites.
OUV: Outstanding Universal Value
The UNESCO concept of cultural and natural significance so exceptional as to transcend national boundaries. The basis on which World Heritage Sites are inscribed. Each WHS has a Statement of OUV adopted by the World Heritage Committee.