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Glossary of Construction Terms - Sections O - S

Sections A - G >>
Sections N - H >>
Sections T - Z >>


Outer string 174
The string farthest from the wall. Compare wall string. Find>>

Overflow pipe 47
A pipe positioned above the normal water level in a cistern/tank. Provided to allow excess water to flow harmlessly to waste in the event of the ball valve failing to close. However, excess water may splash back from paving and lead to internal dampness if this discharges too close to wall of property. Find>>

Oversite concrete 122
See Concrete oversite.

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Parapet/parapet wall 63
That part of an external wall that continued above roof. Top of parapet should be protected by coping or render (which usually includes face of parapet) to prevent rainwater saturating and seeping through wall. Weak point is upstand at junction between parapet and abutting roof covering. Failure in above items can cause water penetration into structure and lead to fungal decay of roof and/or other timbers. Find>>

Patio door 70
An external sliding door.Usually fully glazed, with either a wooden or metal frame (Compare French window).125 Pile
A column of concrete driven into the ground.Provided as foundation for the structure above. The pile is driven either to a stratus which provides a safe load-bearing base for the pile or to a depth which ensures sufficient friction between the sides of the pile and the surrounding subsoil to support the loading of the building. Find>>

Pillar taps 184
Taps with a vertical inlet.Provided on baths and wash hand basins and fixed through holes in the horizontal surface of the bath or basin. Find>>

Pivot sash window (horizontal) 181
An opening light which is hinged at positions along opposite sides. On opening the bottom part of the window, it usually projects outward and the top part inwards. For safety reasons a restrictor should be fitted to prevent young children opening windows too far and stop them from falling out. Find>>

Plaster (on brickwork) 129
A substance applied to internal wall surfaces. Usually based on Portland cement, gypsum plaster of lime putty mixed with sand. Plaster gives jointless, hygienic, easily decorated and usually smooth surface on often uneven background.

Plaster (on lath) 156
A Substance applied to internal wall and ceiling surfaces. Provided in a series of coats to give a smooth. Find>>

Plasterboard - The name usually used to describe Gypsum plasterboard 59, 153, 186, 196
Plasterboard is a stressed skin construction comprising a solid or cellular gypsum plaster core lined with a heavy paper which provides most of its strength. Plasterboard is a low cost and very common form of internal wall and ceiling lining. It offers a good non-combustible base and has a low spread of flame rating. Find>>

Plywood 55
A timber sheet product consisting o a number of veneers of wood bonded together with adhesive with alternate veneers at right angles. Plywood has better strength characteristics and greater dimensional stability than natural wood. It is used in timber framed construction to provide strength and stability to timber framework. Find>>

The face finish to the jointing of a brick wall. The bedding mortar in the joints of a brick wall are cut back to a depth of about 19mm. The pointing replaced the bedding mortar and is more durable and decorative with various types of finishing possible to the surface of the pointing (eg flush, recessed, struck, bucket handle). Also the term pointing can apply to the filling of the joint filling between ridge or hip tiles.

Precast concrete paving 138
Concrete paving slabs cast before being laid in position. Decorative external paving.

Purlin 7
A horizontal mean at right angles to main rafters. Provided to support rafters between the ridge and wall plate and usually positioned approximately halfway up their height, which in turn are supported by means of struts. Find>>.

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Quarter-space landing
A square landing at which a stair turns through 90 degrees. Find>>

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A device for heating a room. Radiators are containers which provide large surface area through which hot water from a boiler circulated and conveys heat to the room usually by radiation but sometimes also by convection. A radiator can also be a moveable oil filled electric unit which can be plugged into any room as needed.

Rafter 11. Find>>

Rainwater pipe See Downpipe 99
Reinforcement provided to resist tensile (longitudinal) stress as in lintels, beams, suspended floors etc. Concrete can be ordinary, precast or prestressed. Problems with R.C. can result from poor design and/or construction, overloading and corroding reinforcement. Corrosion caused by concrete cracking, spalling, delamination, carbonation, inadequate concrete cover, etc.

Reinforced concrete (RC)
Concrete into which steel reinforcing bars or mesh have been set.

Rendering 146
A substance usually applied to external wall surfaces.Usually of cement and sand or similar mix to provide a surface, for appearance or to make the wall waterproof. Cracked external render should be repaired as progressively this will weather and loose key and allow water to get behind render and lead to saturation of wall which in turn can lead to fungal decay of structural timbers internally.

Rendered plinth 127
A skirting of render at junction of wall with external pavings.Usually the plinth covers the dpc and therefore where provided it is not possible to identify material used for dpc (damp proof course).

Retaining wall 140
A wall provided to support a higher level of ground on one side than the other.A retaining wall is designed to withstand the lateral pressure exerted upon it by the rear of the wall. If cracked, bowing and/or leaning this may indicate inadequate design and the wall may require rebuilding. Walls should be provided with weep holes to prevent the accumulation of ground water behind.

Reveal 76
That part of the jamb of a door or window opening which is not covered by the door or window frame.The thickness of the wall visible on either side (internally or externally) of the frame. Find>>

Ridge board 8
A horizontal board forming a ridge. Provided in a double pitched room onto which the upper ends of the rafters of the opposing slope are fixed. Find>>.

Ridge tile 20
A tile which covered the ridge. Provided to make the angle at the ridge waterproof. Find>>

Riser 166
The vertical (or near vertical) face of a step. See Tread. Find>>

Rising damp
The dampness which is drawn up from the ground by capillary action through absorbent building materials. Prevented in modern building by providing a d.p.c. or d.p.m. However, these can still break down. In older properties no dpc or dpm may be installed. Rising damp lead to damp brickwork, fungal decay of timbers and perished plaster. Whilst electronic moisture readings can detect dampness in walls the fungal decay of timber may not be apparent superficially and may well be covered by fitted floor coverings and/or heavy furniture. When rising damp noted it is usual to recommend the property be checked throughout for timber defects albeit physical restrictions and vendors reluctance to allow lifting carpets etc. often prevent this.

Remedial works including waterproofed replastering should be carried out by a specialist firm under long term and meaningful guarantee.

Rodding eye 112
See Access eye. Find>>

Roof boarding 35
Boarding nailed to top side of rafters. Usually in high standard tile and slate roofing to prevent extra bracing to the roof structure and additional insulation and protection to the sarking felt. Find>>

Roof cladding/covering 21
The weatherproofing layer of a roof. On a pitched roof the cladding/covering is usually natural or artificial slate or clay or concrete tiles. (Natural slates shown on drawing). Missing or slipped slates or tiles need to be replaced to maintain roof weatherproofing and whilst isolated replacement is not uncommon this could indicate possible continued regular maintenance in the future and eventual replacement of cladding/covering if this is nearing end of anticipated life expectancy.

Roof decking 69
A term applied to material which spans between roof joists. Provided as base for the roof covering. If roof covering has failed and is leaking then if timber decking this may require replacement as this can distort and also suffer from fungal decay. Metal or other materials may be used for decking.

Roofing felt 34
Sheets of fibre treated with coal for pitch or bitumen or reinforced pvc to provide a waterproof membrane. Laid under slating or tiling which helps prevent driving wind, rain or snow penetrating the roof space. Also provides ‘back up’ if tiles or slates go missing. See Sarking Felt. Find>>

Roof joist 73
A joist carrying a ceiling below and a flat roof above. Provides structure and fixing for roof decking. Roof joists are not normally designed to carry imposed loads.

Roof space insulation 45
See Loft insulation. Find>>

Roof space ventilator 19
A small ventilator to allow of flow of air into the loft space. Find>>

Roof spread
Where the feet of the rafters spread and overturn the walls of the building. Caused as a result of the weight of the roof covering proving too heavy and/or as a result of roof structure being inadequately tied together. Providing spread is not excessive (ie walls not unstable) usually additional tying and/or strengthening timbers will prevent further spread.

Room thermostat
Thermostatic control of central heating fixed to wall.Usually provided in entrance hall away from main entrance door and draughts at approximately 1.35m above floor. Automatically operates boiler to keep building at desired temperature. Room temperature can usually be adjusted by means of lock shields valves fitted to the radiators. Compare thermostatic valves.

A rolled steel joist. A structural mild steel section in an ‘I’ shape. In residential property would normally be used to support first floor structure where through reception room is formed or to support structure of main walls when opening formed for extension etc. It is essential the RSJ is of sufficient section to take the load imposed upon it and the necessary calculations should be carried out by a structural engineer or chartered building surveyor. Such structural works should also be carried out to approval of the Local Authority and in accordance with building regulations.

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Sarking felt
See roofing felt. Find>>

Screed/screeded bed 91
A layer of mortar usually 25mm to 63mm thick. Provided to level off a concrete floor and produce a smooth surface for a later finish. Find>>

Septic tank
A large underground tank for the treatment and purification of sewerage. Usually provided for population up to 100 where no mains drainage available.

Minor movement of the foundation of a building after it has been loaded by the full weight of the building. Settlement is generally of a limited nature, both in amount and extent, not causing major cracking or distress of structure. Compare Subsidence.

Settlement crack 183
See Differential settlement crack.

Shoe 98
See Anti splash shoe.

Sill 80
The projecting feature below a window or bottom member of a window (or door) assembly. Provided to throw rainwater clear of the wall below (See Drip). Find>>

A sanitary appliance. Primarily used for culinary and cleaning activities. Usually made of ceramic ware, stainless steel, enamelled cast iron modern kitchen sinks can be made of Asterite (Manufactured by ICI).

Skirting 200
An upstand covering the base of a wall at the juncture with the floor. Provided to protect base of wall from damage caused by knocking or kicking and to cover junction between wall and floor finishes. Find>>

Sleeper wall 119
A dwarf honeycomb wall beneath a raised timber floor. Provided to support raised timber floor structure and allow for ventilation of sub floor structure.

Sliding sash window 147
A sash window which slides vertically. Usually found in Victorian and Edwardian buildings. Regular maintenance required to ensure window functions adequately. Also, sliding sash prone to sticking in guides, rattling and draughts.

Soaker 31
A piece of flexible metal dressed under a steeped flashing. Bonded in wall with slates or tiles at an abutment between a sloping roof and a vertical wall to make a weatherproof joint. Find>>

Soffit board 10
The board forming the underside of overhanging eaves.Usually nailed to rafters or bearers. Nowadays the soffit board is provided with regularly spaced grilles to ventilate roof space. Ventilation grilles could prove beneficial if fitted into existing properties’ soffit boards.

Soil drain
A drain for carrying foul sewage. Compare combined drain, foul drain and surface water drain.

Soil pipe
A pipe to convey sewage from a wc. pan to a soil stack. Find>>

Soil stack 113
A vertical, above ground pipe. Provided to convey sewage from sanitary fittings to the ground level where it enters the soil drain. Its head is taken through or left above roof level and left open to ventilate the drain and prevent traps on the fittings being siphoned off.

Soldier arch 148
A flat arch in brickwork. Provides a more decorative finish to external head of window or door than a concrete lintel. Bricks can be held in position by adhesion between mortar and the bricks but this method of prone to failure. Some form of additional support to the arch may sometimes be required to prevent bricks slipping.

Solid brickwork 155
See Brickwork (solid).

Spalled brickwork
Where the face of brick has eroded due to weathering usually by frost damage.When spalling occurs the hardened water resistant face of the bricks is eroded away and the bricks become highly absorbent. This can cause saturation of the bricks and lead to internal dampness and consequently fungal decay of internally opposite adjacent timbers. Spalled bricks can either be faced with a waterproof render or cut our and replaced.

Stepped flashing 32
A cover flashing usually of flexible metal. Provided to help make the joint between a sloping roof and an abutting wall weathertight. The stepped flashing is dressed into the joints of the walling, stepping down from joint to joint always keeping a minimum height of flashing of 75mm. It is dressed down over the soaker. Find>>

Stone chippings 65
Usually about 13mm chippings spread over a felt roof on a coating of chipping compound. Provided to protect the weatherproofing, give additional fire resistance and increase solar reflectivity. If walked on they can puncture felt so if access required across roof, boards should be used to help spread the load.1 Stop end (to gutter)
The blanked off end to a gutter. Find>>

Strip concrete foundation 93
A strip of concrete of uniform width. Provided as foundation for the structure above. The strip foundation is the most common used in residential property of up to four storeys in height built of brickwork and designed to support the loading of the building and spread it uniformly onto the stratum below. The depth of the strip foundation will be dependent on the stratum onto which it is laid but never less than 600mm. Find>>

Strut 6
A sloping roof beam. Provided to give support to a purlin. The foot of the strut is usually fixed to a wall plate bedded in mortar on top of a load bearing partition and the top spiked and/or notched to the purlin. Find>>

Stud 157
A vertical timber in a timber stud partition. Provided as framing for partition between a sole plate and head piece. Find>>

Stud partition 188
A timber framed partition. A lightweight, usually non-load bearing partition comprising vertical timber studs fixed between a sole plate and head piece and stiffened at mid span by nogging pieces. In older properties normally lined with lath and plaster but since about 1940 lined with plasterboard. Find>>

The sinking or caving in of the ground, or the settling down of a structure to a lower level. If the settling down is limited and even in extent, the phenomen is known as settlement and is considered quite normal. It should not lead to large cracking of the structure. If movement is extensive and uneven, leading to cracking of the structure, this is called subsidence and could be caused by insufficient spread of inadequately constructed foundations, inconsistency in the subsoil which was not noticed at the time of pouring the foundations, or some external cause such as leaking drains, dewatering of the subsoil by tree root action or mining activity. A structural engineer or chartered building surveyor should be called in to advise if subsidence is present. Underpinning may be required to prevent subsidence.

Subsidence crack 183
See Differential settlement crack.

Surface water drain
A drain which only carries surface (or storm) water. Compare Combination drain, Foul drain and Soil drain.

Swan neck 36
A pipe in the form of an ‘S’ bend. Usually provided from the junction of a gutter to a downpipe to bridge between overhanging eaves and face of wall. Find>>

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