Glossary

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A B C D E F G H I K L M N P Q R S T V

H

Head or end lap

With double-lap tiling or slating, the length by which a course overlaps the next but one below.

Heritage asset (for heritage policy)

A building, monument, site, place, area or landscape identified as having a degree of significance meriting consideration in planning decisions, because of its heritage interest. Heritage asset includes designated heritage assets and assets identified by the local planning authority, including local listing (as defined in the National Planning Policy Framework 2012).

Hip

The external angle formed where the sides of two adjacent roof slopes meet (cf valley). It occurs where the end of a pitched roof is sloping, rather than, as with a gable, standing vertically.

Historic environment

All aspects of the environment resulting from the interaction between people and places through time, including all surviving physical remains of past human activity, whether visible, buried or submerged, and landscaped and planted or managed flora.

Historic environment record

Information services that seek to provide access to comprehensive and dynamic resources relating to the historic environment of a defined geographic area for public benefit and use.

Hydrated lime or dry hydrate

Calcium hydroxide (Ca(OH)2) formed as a dry powder when any lime is slaked using an exact amount of water (cf lime putty). Not to be confused with hydraulic lime. It is possible to obtain hydrated hydraulic lime or hydrated non-hydraulic lime.

Hydraulic or water lime

(i) Natural hydraulic limes are prepared from limestone with reactive silica and alumina impurities. The lime reacts with the impurities in the presence of water to form calcium silicates and aluminates (cf non-hydraulic lime), in addition to the calcium carbonate that contributes to the hardening process when exposed to the air. They are classified under BS EN 459: Part 1: 2001 as NHL 2, 3.5 or 5, in order of increasing strength.

(ii) Natural hydraulic limes with an additive are classified as NHL-Z, while HL denotes an artificial hydraulic lime. Since manufacturers do not have to state whether the additives include Portland cement or hwat the percentages are, these products should be avoided in conservation work.