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Calcium Chloride

(CaCl) An accelerator previously used in the construction of concrete. Now rarely used as it can corrode steel reinforcement and lead to a loss in strength.

Calcium Silicate Bricks

Low cost bricks made from sand/flint-lime which are frost and sulphate resistant. They are however prone to high moisture and thermal movement. Initial shrinkage can often be a problem and movement joints should be regularly provided in brickwork.

Capillary Action

The natural tendency of a liquid to be sucked into the small cavities of a porous material or joints. Can often lead to damp problems.


The natural hardening of the outer surface of concrete causing irreversible shrinkage and reducing alkalinity. Steel reinforcement within this zone is prone to corrosion, expansion and failure.

Casement Window

A window that has one or more sashes hinged to open. Most commonly side or top hung opening lights.


A tight joint created by forcing a jointing material or sealant into a gap.

Cavity Closer

Material inserted at a door or window opening to close the cavity of a cavity wall. Traditionally completed in masonry incorporating a vertical damp proof course. More modern insulated cavity closers are now available which reduce cold bridges.

Cavity Wall

A wall that comprises of two leaves of masonry separated by a cavity.

Cavity Wall Insulation

Various insulating material provided to the cavity within a cavity wall to increase the thermal efficiency of a dwelling. Careful installation is required to prevent water penetration or cold bridging.

Cavity Wall Tie

Ties used across the cavity in a cavity wall connecting the two leaves of masonry together. Usually formed in metal and can be prone to corrosion leading to their failure, cracking in masonry and structural movement.


Usually refers to Ordinary Portland Cement (OPC) which is used as a binder to set and harden materials together. Used in the formation of concrete, mortar, render and many other building materials.

Central Heating

Method by which a building is heated by a central boiler, usually providing heat to radiators. Other systems included warm-air via ducting or wet under-floor heating.

Cesspool or Cess Pit

A tank, usually underground, that holds waste water and sewerage. There should be no discharge from the tank and it will require regular emptying.


The side elevations of a dormer projection.


A building board comprising of compressed wood chips set with a synthetic adhesive.

Circuit Breaker

An electrical switch that trips automatically to break the circuit if there is an over-current or earth leakage. Can be easily reset once the problem is rectified. Often found in 'Consumer Units' as 'Miniture Circuit Breakers (MCB's)' or a 'Residual Circuit Device' (RCD).

Cold Bridge

A 'cold spot' formed in the structure due to materials with a different thermal capacities. Cold bridges are undesirable as they can lead to condensation problems.

Cold Roof

A roof in which insulation is situated at its base next to the ceilings of the property and a ventilated void formed above. A cold roof may be pitched or flat. If insufficient ventilation is provided to the void, moisture-laden air can cause condensation problems. See also Warm Roof.

Collar (Beam/Tie)

A horizontal beam or tie, usually timber, which connects coupled rafters together, normally at their mid-span to prevent 'Roof Spread'.

Combination Boiler

A boiler that provides central heating and instantaneous hot water for domestic purposes. They usually form part of a pressurised system and have no requirement for water storage tanks.

Combustion Gases

Gases created by the combustion of fuel or other materials. Usually toxic or noxious, they require the efficient removal from a dwelling for health and safety reasons.


A mixture of cement, aggregate, water and admixtures in various ratios to provide a versatile building material which is strong in compression. An alkaline material that is prone to 'Carbonation' and 'Sulphate Attack'.


The point at which water vapour turns into liquid when the air temperature drops below the critical dew point and cannot support any more moisture. Usually found when warm moisture-laden air comes into contact with a cold material. Condensation can form on the surface of a material or within a material itself, which is known as 'Interstitial Condensation'.

Consumer Unit

A modern form of 'fuse box' where 'Circuit Breakers' are located and the electrical supply is distributed around a building.

Condensing Boiler

An energy efficient form of boiler that cools the flue gases to condensate, thereby allowing it to extract more of the available heat from the fuel source. The condensate is acidic and requires draining to an appropriate receptacle. Water vapour is given off via the flue, which is often fan assisted as it requires a high exit velocity.


The finished top course of a wall, usually formed of stone, concrete or brick. Decorative but also designed to shed rainwater away from the structure.


A stepped projection from a wall, usually brick, designed to support loading from above.


A decorative moulding at the top of a wall. External cornices help to shed water and protect against the spread of fire. Internal cornices often hide the gap between the wall and the ceiling.


Timber battens fixed over a secondary barrier but beneath the external roof coverings, running parallel to the rafters of a roof to provide a gap to allow the run off of any driven rainwater.


A concave moulding hiding the junction between an internal wall and a ceiling.

Curtain Walling

An external decorative fa├žade cladding to a building, often supported by a metal frame.


Area of land belonging to a dwelling.