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Glossary of Construction Terms - Sections Terms A - G

Sections H - N >>
Sections O - S >>

Sections T - Z >>


Access eye 112
An opening in a pipe or drain.Allows pipe or drain to be rodded through in event of blockage. Usually positioned at a change in direction (or close to) of pipe or drain and is closed by plate bolted into position. Find>>

Air brick 128
A perforated brick specially made for building into walls.Allows the passage of air below a raised timber ground floor. If blocked or number of air bricks inadequate stagnant/damp air can lead to fungal decay of floor timber. A metal ventilating grill is common alternative to an airbrick.

Air dry
Air dry means in equilibrium with a typical atmosphere with a relative humidity of between 40/65%. All building materials have some moisture content. This is perfectly normal and the percentage content differs for each material at any given relative humidity. Dampness occurs when a material is wetter than air dry.

Angle tie 48
A horizontal timber across the corner of a building, tying together wall plates. Provided to prevent overturning of walls at the corner of the building due to forces imposed by the roof framework as a result of a hip rafter carrying the ends of several jack rafters. Find>>

Anti-Splash Shoe 98
The angled section at the base of a rainwater pipe. Provided to direct the flow of rainwater away from the building preferably into a rainwater gulley. If missing rainwater could splash back up face of building over the damp proof course and lead to internal dampness and consequently fungal decay of internally adjacent timber. Find>>

Apron 142 (to lead roofing)
A dressing over an upstand to weatherproof a joint covering and vertical surface. Provided to weatherproof a joint between a roof covering and vertical surface. Top edge of apron tucked and wedged into groove in brickwork run with a cement and sand fillet (See Upstand to lead roofing). If defective or missing allows rainwater penetration down behind upstand which can lead to fungal decay of roof and/or other timbers.

Architrave 164
Trim, often of wood, to perimeter of door or window frame. Provided to cover the joint between door or window frame and the adjoining wall finish. Find>>

Asphalt roofing
Roof covering in two layers laid on a bituminous sheathing felt.Provides total impervious surface if properly laid. More expensive but longer life expectancy than built up roofing. Minor splits/cracks in asphalt can be repaired in short term to help extend life. However, failure allows rainwater penetration to roof structure which can lead to fungal decay of roof and/or other timbers. 

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Ball cock/Ball valve 43
Valve on the supply pipe of a water tank or wc. cistern. Provided to shut off water supply when tank or wc. cistern full. If valve becomes defective then water level will rise to level of overflow pipe which will discharge, normally into external paving. Defect may be intermittent. Find>>

Baluster 172
Post or pillar in a balustrade – also called a banister. Provided at regular centres as infill from handrail to floor level at edge of landing or stair or balcony. Forming part of a balustrade. Find>>

The handrail and balusters from the handrail down to the floor at the edge of a landing or stair or balcony.  

Bargeboard 23
A board inclined to the pitch of a sloping roof surface. Provided to cover the end of the roof timbers at the gable. It is usually placed outside the line of the gable wall so that the roof covering oversails the wall and protects it. Find>>

Bath 189
A large container used for washing the body. Defects (eg leaking pipework, disconnected/missing overflow) not always possible to ascertain. It should be ensured seal around perimeter of bath is serviceable to prevent water running down behind bath which can lead to fungal decay of floor timbers below. Find>>

Battening 13
A piece of rectangular softwood. Fixed to rafters onto which roof coverings are nailed or hung. Find>>

Bay window 131
A window which projects beyond the line of the general wall surface. Sometimes foundations to bay windows in older properties is less than wall into which it is tied. This can result in differential settlement of bay requiring underpinning or sometimes rebuilding.

Bearer 44
A horizontal timber used as a support. In this instance a bearer is used to support a water tank and spread weight of tank across several ceiling joists and onto partitions below. Find>>

Beetle infestation
See Wood boring insect infestation.

Benching 109
A sloping surface constructed of concrete on each side of a channel in a manhole. Provided to stop accumulation of solids and encourage complete drainage. Find>>

Bitumen felt roofing 66
See Built up roofing. Find>>

Blinding 88
A dressing of ash, fine gravel or dry coarse concrete on a hardcore bed.Provided to fill the interslices of a hardcore bed before pouring concrete. Find>>

Block inner skin (to cavity wall) 82
A wall of blocks, laid to bond and bedded in mortar forming part of a cavity wall. The most usual internal leaf of a cavity wall tied to the outer skin with cavity wall ties (See Cavity wall ties). Find>>

Block internal partition 179
A partition built of blocks, laid to bond and in a mortar. Provided to separate adjacent rooms and bonded/key in to outside walls of intersecting partitions. Can be load bearing or non-load bearing. Find>>

An appliance to heat water and/or provide central heating. Provides domestic hot water and central heating (sometimes called Space Heating). Usually fired by gas, oil or solid fuel. Boilers can be floor mounted with flue, back boilers fitted into a fireplace with existing flue (which needs to be lined) and wall mounted balanced flue or combination. Normal life expectancy between 15-18 years.

The method of laying bricks and blocks so that their vertical joints in succeeding course, do not coincide. The method of tying in a partition to an outside wall or intersecting partition. (1) Bonding (eg English, Flemish, Stretcher) increases the stability and load bearing capacity of the wall. (2) Bonding normally occurs at every course or every 3 courses and increased the stability of the partition.

Boot lintel 79
A (reinforced) concrete lintel with a projection at the foot of its’ front face. Can be provided in solid cavity wall construction. The main part of the lintel supports the wall or inner skin respectively, with the reduced depth of the projection not spoiling the appearance of the wall. Proprietary all steel (eg Catnic) boot lintels now commonly in use. Find>>

Borrowed light 163
A window in an internal partition. Provided to distribute natural light from one room or area to another. Find>>

Branch bend 107
The channel linking branch drain to main drain channel in a manhole.Provided to introduce effluent from branch drain into the main drain in the direction of flow. Find>>

Branch drain 101
A subsidiary drain run. Provides an inlet to a main drain (See Main drain). Find>>

Breather paper 54
A moisture resistant and water repellent paper (building paper) which is permeable to water vapour. Provided to prevent damage from water bridging the cavity (after construction) and allow internal moisture (residual in the structure or from internal humidity) to escape. Find>>

Bressummer 145
A large lintel/beam over an unframed opening.Provided to support walling erected directly upon it. In older properties usually timber which may sag to timber deterioration or creep deflection. Creep may be tolerated while deterioration will lead to failure. If distortion of the main wall above a bay window is present exposure may be necessary to establish if replacement bressummer required. 

Brick external cladding (to timber framed wall) 52
A brick wall forming the external facing to a timber framed property. Non-load bearing brick skin, decorative and protective of the lead bearing timber framework. Find>>

Brick inner skin (to cavity wall below damp proof course) 85
A brick wall, laid to bond and in mortar. Normally of common (eg Fletton) bricks.

Brick outer skin (to cavity wall) 71
A brick wall forming part of a cavity wall. The external leaf of a cavity wall tied to the inner skin with cavity wall tie (See Cavity wall ties). Find>>

Brickwork (solid) 155
A solid wall built of bricks, laid to bond and in mortar.Used to be the most common load bearing external wall construction. Mainly finished with fair faced bricks and pointed or rendered. Minimal maintenance required but as properties age partial or complete repointing or re-rendering respectively may become necessary.

Built up roofing 66
Three layers of bitumen felt bonded together with bitumen dressed with stone or spar chippings or other solar reflective
treatment.Method of weatherproofing a flat roof. Relatively short life expectancy (about 15 years) which to a large extent depends on standard of workmanship when laying. Patch repairs possible but if leaking can lead to fungal decay of roof and/or other timbers. The stone or spar chippings or other  solar reflective treatment are provided to help prevent damage due to excessive thermal movement of felt. Find>>

Butterfly roof
A roof where there are two pitched surfaces inclined towards the centre of the building. Where this method of roofing is provided the roof covering itself is no more problematic than normal. However, the extensive lengths of flashings to the parapets and party walls above roof level and the sheet metal lined centre valley gutters are frequent points of failure which when fail cause rainwater penetration into roof structure which can lead to fungal decay of roof and/or other timbers. 

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Casement windows (side hung) 132
A window in timber, metal or plastic. Part of a casement window is hinged to open.

Cavity (to cavity wall) 94
The void between the two skins of a cavity wall. Provided to increase the thermal insulation and weather resistance of the wall.  The cavity must be kept clear (except for wall ties and insulation) and not bridged and a dpc must be provided around the perimeter of openings in cavity walls otherwise dampness can occur internally. Find>>

Cavity (to timber framed wall) 53
The void between the timber frame and external cladding in a timber framed property. Provided to increase the thermal insulation and weather resistance of the wall. This cavity must not be insulated as it must be kept free for ventilation. Find>>

Cavity fill 84
Lean mix concrete filling of cavity from top of foundations to ground level. Provided to make wall below ground level solid and withstand the lateral pressure exerted by the earth on either side of the wall and prevent wall caving in. Find>>

Cavity wall insulation
A material insulating a cavity wall. Provides additional thermal insulation. In existing properties the cavity can be insulated with polystyrene pellets, plastic foam or blown mineral wool. To comply with current Building Regulations in new properties mineral wool slab/blocks are built into cavity during construction. Provision also impedes transmission of sound and vibration. Find>>

Cavity wall tie 95
A metal or plastic device which is built into both skins of a cavity wall. Provided to tie both skins of a cavity wall together.  In older properties where non-stainless steel ties were used failure of ties can occur resulting in instability and bulging and horizontal cracking in wall. Replacement of ties can be carried out if necessary.

Ceiling joist 4
A joist carrying a ceiling below and no floor above. Ceiling joists are not normally designed to carry imposed loads. Therefore loft spaces should not be used to store heavy goods or used as rooms unless strengthened. Load bearing capabilities of ceiling joists should be checked if resting water storage tanks in loft. Find>>

Centre valley gutter

A gutter (usually in lead) formed for the removal of rainwater from a butterfly roof. Provided along the length of the roof, usually discharging into rainwater pipe via opening in parapet wall. If failed or leaking can lead to fungal decay of roof and/or other timbers.

Centre valley roof
See Butterfly roof.

Central heating
A form of heating to heat whole building, as opposed to individual sources in different rooms. The most common form is an independent gas boiler to radiators. Other forms include gas warm air, electric underfloor and ceiling heating. Electric night storage heaters are not central heating as although these can be installed in rooms as required or provided to heat the whole building they are usually individually controlled.

Central heating header tank 46
A feed and expansion tank. A tank in a central heating installation to provide cold water to replenish water which has evaporated or expanded on heating up. Find>>


A large underground chamber for the collection of foul drainage. Provided where there are no main drainage services.  Built in brick or concrete with a waterproof rendering or sometimes reformed in glass reinforced plastic. Periodic pumping out is required.

Channel 105
A semi-circular open pipe. The channel is in the main drain run in a manhole. Find>>

Chimney pot 29
The topmost feature of a flue. Provided to discharge the smoke and combustion fumes above the level of brickwork of the chimney stack. Bedded in flaunching of cement mortar. If chimney pot is removed the flue should be capped and ventilated. Find>>

Chimney stack 27
The part of a chimney which rises above the roof. Provided to discharge the smoke and combustion fumes above the level of the roof.  Problems normally associated with stacks are defective pointing and flashings. Also, in older properties sulphate attack can result in curved stacks. Sulphate attack is irreversible and demolition of affected stacks may be required. Find>>

Circuit breaker
Device to switch off overloaded electrical circuit. Provided on each separate circuit in a property to automatically protect circuit against damage from excessive current flow.

Cistern 193
See Flushing cistern. Find>>

Cold water storage cistern/tank 42
A tank used for the storage of cold water. A tank usually fed by the mains and provided to feed the hot and cold supplies to the various sanitary appliances in a building (except kitchen sink which is mains fed). Also used as an expansion tank in a hot water system with an indirect cylinder to allow the water in the primary circuit to expand on heating up. Should be lagged to prevent water freezing (See Lagging). Galvanised tanks suffer from corrosion which eventually leads to failure. Find>>

A horizontal roof beam. Provided to tie together an opposing pair of rafters and is often positioned approximately halfway up their length. Collars are usually fixed to every third or fourth pair of rafters. Find>>

Combined drain
A drain in which foul and surface water drainage is discharged into one sewer. Compare foul drain, soil drain and surface water drain.

Concrete drain bedding 103
A concrete bed laid under a drain pipe. Provided to give continuous support under pipe run. Find>>

Concrete manhole base 108
A concrete base to a manhole. Provided to give base off which walls to manhole are built and also a base onto which channel, and benchings are laid.

Concrete oversite 122
A layer of concrete. Provided under ground floor and laid on the earth or a hardcore bed.

Concrete slab 89
A layer of concrete. Provided to form a floor and either sandwiching (between two thin slabs) or laid over a damp proof membrane. Find>>

Consumer Unit

Coping 60
A capping to the head of a wall. Provided to give protected to the head of a wall to prevent rainwater penetration through top of wall. A damp proof course of tiled creasing course should be provided beneath a coping to prevent rainwater affecting the brickwork through the top of the wall. Find>>

Cornice 154
A decorative moulding. Provided to give a period feature at the junction between wall and ceiling.

Coving 197
A concave moulding. Provided at the juncture between wall and ceiling. Find>> 

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Dado rail
A rail set on a wall. Provided at the head of a dado where the lower part of a wall is decorated differently from the upper part. Usually fixed about 1m above floor level.

Damp proof course (dpc) 62, 78, 83, 120
A barrier of imperious material. Provided to prevent rising dampness in a wall from the ground. Usually incorporated in wall approximately 150mm (not less) above external ground level. However, they are also required beneath copings and around window and door openings in cavity walls etc. Most common materials for dpc’s are felt, pitch polymer, slate and silicon injection. Less common methods include capillary clay pipes or electro-osmosis which have not proved to be very successful. See DPC. Find>>

Damp proof membrane (dpm) 90
A barrier of imperious material. Provided to prevent the spread of moisture in a floor from the ground. Usually incorporated into or under a concrete floor slab. Most common materials for dpm’s are polythene sheet and bituminous emulsion (eg Synthaprufe or similar). Find>>

Dead light 133
A window or part of a window which does not open. To provide natural light.

Differential settlement crack 183
Crack at juncture of new work with old construction or two connected elements of a structure built at the same time. Can take the form of sinking or tilting. Establishing of vernier crack markers and monitoring of movement for at least three months is required if continuing movement is suspected. This work should be carried out by a structural engineer or chartered building surveyor, who will usually be able to advise what (if any) remedial works will be required at end of monitoring period. The monitoring period will depend upon the expected cause and rates of movement. For example differential settlement can occur between old and new construction as a result of the soil under the element adjusting to the weight imposed upon it. Also the back addition of Victorian property can suffer by settling away from the main element of the building. Find>>

Door frame (to external door) 116
The frame to a door. The frame usually is rebated and is of a stouter section than a door lining (compare door lining). Find>>

Door lining (to internal door) 162
A lightweight alternative to a door frame. Usually only provided to internal doors. The lining extends the full width of the jamb. It is occasionally rebated for the door but more often has a planted stop (compare door frame). Find>>

Dormer (window) 18
A vertical window set into and projecting from the slope of a pitched roof.Provided where a room or rooms are contained within roof space. Like any projection through a roof the weak points tend to be the flashings and aprons.  Also cheeks and roof if partially felted are prone to failure and as a result dormer windows are more likely to suffer from rot. Find>>

Dormer cheek 23
The vertical side of a dormer window. The cheeks (roof, flashings and apron) to the dormer should be serviceable as failure can result in rainwater penetration and lead to fungal decay of roof and/or other timbers. Find>>

Dormer Window 19
Window built into the pitch sides of a tiled roof. Find>>

Double glazing 77
Two layers of glass separated by an air space. Provision improves thermal and acoustic insulation. Glazing must be hermetically sealed to prevent condensation on side face of glass. Find>>

Downpipe 99
A rainwater (or water) pipe. Provided to collect rainwater direct from a gutter or via a hopperhead collecting other rainwater or waste pipe.  It is essential that downpipes are free from leakage. Otherwise, saturation of external wall can occur which can lead to fungal decay of timbers internally opposite. Find>>

DPC 62, 78, 83, 120
See Damp Proof Course. Find>>

Dragon tie 48
See Angle tie. Find>>

Drain bedding 103
A bed laid under a drain pipe. See Concrete drain bedding. Provided to give continuous support under a pipe run.

Drip 81
The groove or recess formed on the underside of the projecting part of a window sill. Provided to encourage rainwater to fall off the sill rather than flow back towards the wall below. See Throating. Find>>

Drip edge 139
The lower edge of a flexible metal roofing. Provided to overhang edge of flexible metal roofing (eg lead) to encourage rainwater to fall off rather than flow back towards the wall or window below.

Dry rot
A wood destroying fungus (See Serpula Lacrymans). Attacks wood (particularly softwood) in damp un-ventilated conditions. Consists of cotton wool like fungus and a network of feeder strands which can extend several feet over brick and steel and may penetrate behind plaster and through brickwork. One of the major problems in eradicating the fungus is to ensure that the feeder strands are killed or rendered ineffective. The fungus breaks down the cellulose in the wood and the timber becomes brittle and suffers from cubodial cracking. Growth rate is about 1m per year. When dry rot is found, full investigation and exposure of concealed areas will be required. Affected timber will require to be treated or cut out and replaced and surrounding area will require to be sterilised (which will necessitate hacking off plaster, removal of any panelling etc.) to approximately 1m past last traced of the feeder strands. 

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Earth leakage circuit breaker
Automatic switch mechanism giving protection against possible electrocution.Required to comply with IEE Regulations for Electrical Installation (from 15th Edition). Automatically switches off electrical supply at the consumer unit where property badly wired, wrongly, wired, or damaged equipment being used. Offers protection against contact with frayed cable, bad jointing and accidental electric shock.

Eaves 33
The bottom of a pitched roof slope. (or area of tile hanging). Usually eaves overhanging the wall to prevent rainwater affecting the brickwork through the top of the wall. The eaves course of the roof covering usually discharges into a gutter fixed to the eaves fascia. Where roof covering is in slate or plain tiles a double course of slates or plain tiles should be provided at eaves. Double course should also be provided for area of tile hanging.

Eaves fascia 17
A vertical board nailed to the feet of the rafters. Provided as a fixing for the gutter to prevent rainwater affecting the feet of the rafters. Find>>

Eaves plate 9
A wall plate. Provided to span between interrupted sections of wall and between the walls, supports and rafters.

Expansion pipe 41
A discharge pipe over a cold water storage tank. Provided from an indirect hot water cylinder to provide an escape route for steam or water should the water in the system boil. Find>> 

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Fascia board
See Eaves fascia.

Felt roofing 66
See Built up roofing. Find>>

Fillet 25
A mortar strip of triangular cross section. Provided to make the junction of two elements meeting at right angles waterproof. Unsatisfactory method of making junction waterproof as slight movements in roof coverings cause fillet to crack and fail which allows water to penetrate roof structure which can lead to fungal decay of roof and/or other timbers. Find>>

Fire back 176
The back wall of a fire place. Fire backs are made from fire clays and provided to prevent heat of the fire damaging the wall behind. Find>>

Fire place 177
A recess formed in a wall for a fire.

Firring 72
Longitudinally splayed timber batten.Nailed to top of roof joists to flat roof before the insulation board and roof decking is fixed to give the roof a fall to allow rainwater to drain.

Fixed light 133
See Dead light.

Flashing (to Built Up Roofing or other roofing, in similar circumstances) 64
The part of a roof covering turned up against a vertical  surface. Provided to weatherproof a joint between a roof and a vertical surface. If split or damaged can allow water penetration into roof structure which can lead to fungal decay of roof and/or other timbers. Find>>

Flaunching 28
The cement mortar bed to the top of a chimney stack. Provided as bedding for chimney pots and to protect the top of the stack from rainwater penetration and frost damage. If defective, chimney pots become dangerous and could blow off stack. Find>>

Floor board 149
A board forming part of a floor. Usually plain edged or tongued and grooved (abb. T&G), T&G boards prevent dust and draughts as boards interlock and look better if no fitted floor coverings.

Floor insulation 91 Find>>

Floor joist (to raised timber floor) 118
A timber beam spanning between sleeper walls. Support for floor boards or floor decking which are nailed to joists.

Floor joist (to suspended timber floor) 151
A timber beam spanning between walls.As floor joist above.

Flue 169
A duct from a fireplace. Provided to convey smoke or combustion gases from a fireplace to the atmosphere. Smoke from slow burning open fires in the unlined flues can lead to cracking of the external face of the flue or staining or cracking of the plaster surface internally particularly when flue is on outside wall. Find>>

Flushing cistern 193
A cistern provided with a device for rapidly discharging its contents.A flushing cistern forming part of a water closet which may be integral with the wc. pan or separate and joined by a flush pipe.  Provided to carry away the contents of the wc. pan when operated.  Usually of ceramic ware. Find>>

Foam lagging 173
Lagging applied to hot water cylinder at manufacture.Provided to prevent excessive heat loss through the wall of cylinder and consequently save energy and reduce fuel bills (compare Lagging Jacket).

Footing 125
The widening of the base of a wall. A method of constructing foundations at end of 19th century. Very rarely used nowadays.

Foul drain
A drain intended to convey all manner of domestic effluent with the exception of surface water. Compare Combination Drain, Soil Drain and Surface Water Drain.

French Window

A casement door. A fully glazed door or one of a pair of doors.  The door is always hinged  (compare Patio Door).

Front apron flashing 26
A one piece flashing where a vertical surface of chimney stack or dormer window penetrates an inclined roof. Provided at lowest point of chimney stack or dormer window to make junction weatherproof. If defective can lead to damp penetration into roof structure and fungal decay of roof and/or other timbers. Find>>

Fungal decay
Decay by an organism that lives off timber on which it is situated. See Dry rot and Wet rot which are explained separately. There are also other forms of fungal decay but dry and wet rot are the most common.

Device to cut off overloaded electrical circuit.Provided on each separate circuit in a property to protect circuit against damage from excessive current flow by opening the circuit on the melting of fuse element.Fuse box/board
A housing for fuses. Provided until recently by current installations use. Consumer units with circuit breakers (See Consumer unit). Not necessarily unsafe but overtaken by technology. 

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Gable/gable end
The triangular part of the end wall of a building with a double pitched roof. Wind suction on unbraced gable roofs and untied gable walls (especially trussed rafter roofs of the early 70’s) can cause sudden collapse of gable in strong winds.

Gable board 23
See Barge board. Find>>

Gauge of battening 14
Spacing of battening for fixing of roof covering. Battens need to be spaced so as to allow at least two thicknesses of roof covering at every point and sufficient lap to prevent water running off one tile/slate and into the joint of the two tiles/slates below. Find>>

Ground beam 124
A beam cast in a trench on top of pole or pile cap. Provided to avoid expense of digging deep trenches for foundations to wall built on heavy shrinkable clay soil. Usually the ground beam is reinforced plus there are bent reinforcing bars cast into the beam and top of the pile or pile cap.

Ground Heave

Gulley 97
A drain fitting into or over which a downpipe discharges. A defect in the gulley causing leakage can, in some soils, lead to erosion of load bearing strata beneath foundations and cause structural instability. Find>>

Gulley grating 96
A cover to the top of a gulley. A cover of metal or plastic which allows entry of rainwater but prevents entry of leaves, twigs, rubbish, etc. Find>>

Gutter 49
A channel for the removal of rainwater. Where removal of rainwater is from around eaves of a roof a more accurate description is eaves gutter. It is important to ensure gutter remains watertight and is recommended that guttering be cleared out each year, preferably at end of Autumn to prevent blockage and overflowing.

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