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A granular material, usually natural stone, used as the main constituent of concrete. Graded as coarse, fine or a mixture. Artificial aggregates can be added to enhance performance, colour or finish.

Air Admittance Valve

A valve fitted to sanitary plumbing in addition to a soil and vent pipe in order to relieve differences in air pressure within the system.

Air Brick

A specially made brick with uniform holes through its width with the purpose of allowing a through flow of ventilating air, usually to sub-floor or roof voids. Can also be plastic or metal.

Air Lock

A bubble of air trapped within pipework, preventing the flow of water. Often overcome by 'bleeding' the system to release the trapped air.


An expanded metal mesh with a rounded or angled edge, intended to form a durable corner for plastered walls.


Thick lining paper often embossed with decorative patterns.

Approved Documents

Technical documents providing the approved standard associated with Building Regulations compliance. The Approved Documents comprise fourteen Parts: A to P, each covering a specific issue.


A joinery component comprising a profiled moulding fixed around a window or door frame to hide the gap between the frame and adjoining wall. Joints are usually mitred.


A naturally occurring material often used in the past for various building and insulating materials due to its heat resisting and reinforcing properties. No longer used due to health risks associated with breathing in microscopic fibres. Specialist Advice should be sought regarding its identification, encapsulation or removal.

Asbestos Cement

A cement product containing asbestos fibres for reinforcement. Please see Asbestos above.


A mixture of bitumen and inert mineral filler, usually sand, clay or limestone. Heated for application and becomes hard and impervious when cooled. Normally used as a roof or path covering.