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Glossary of Construction Terms - Sections T - Z

Sections A - G >>
Sections H - N >>
Sections O - S >>



A waterproof membrane set on the outside of basement walls and subsequently protected by an outside skin, often of brickwork. Usually of asphalt, butyl rubber or bitumen/polythene sheet suitably jointed. Tanking to the basement floor is laid under loading coat which is provided to prevent tanking from being displaced by water pressure beneath it.

Tell-tale 182
Crack monitoring device. Should be installed and monitored by a qualified structural engineer or chartered building surveyor. Sliding perspex tell-tales are either screwed or fixed with epoxy rein to each side of the crack. The calibrated scale on the face of the tell-tale is then monitored to establish extent and direction of movement. (See ‘Differential settlement crack’). Compare Vernier crack markers. Find>>

Thermostatic valve
An automatic valve fitted to individual radiators. Provided to maintain desired temperature in each room rather than from a centralised thermostat. Compare Room thermostat.

Throating 81
See Drip. Find>>

Tie bar 143
Consists of a tie plate and tie rod. The tie rod is passed through the external wall and anchored between the tie plate and floor joists. Provided to restrain distortion or untied flank walls from further movement. Tie bar forms are usually circular, S or X shaped or CPlll stainless steel restraint straps. Their provision, design and spacing should be calculated by a structural Engineer or charted building surveyor. The provision of tie bars does not necessarily render a property unstable or unmortgageable but they may deter some prospective purchasers and therefore restrict marketability and therefore could adversely affect the value of the property.

Timber frame construction 52 to 59
Comprises load bearing preformed timber framed walls erected on a prepared ground slab. The walls are bolted together and clad externally with a non-load bearing external skin of brickwork or alternative type of cladding as weatherproofing.

Timber framework (load bearing) 56
See Timber frame construction. Find>>

Timber stud partition 188
See Stud partition.

Tingle 19
A strip of lead about 37mm wide.Used to refix slipped slates on a pitched roof. Provision of tingles on a slate roof would suggest tied nails and therefore continued regular maintenance to replace slipping slates in the future and eventual replacement of the slate covering which could be nearing the end of anticipated life expectancy. Find>>

Transom 136
A horizontal member which separates the lights of a window. Not to be confused with glazing bars which divide lights into panes and can be vertical or horizontal. Compare Mullion.

Trap 192
A means of retaining water in a pipe. Provided to avoid the passage of drain smells up the pipe, usually taking the form of a U-shaped bend or bottle trap (as shown to bath and wc pan on drawing). Find>>

Tread 16
A horizontal component of a stair on which one stands. The Building Regulations quote parameters for the going (the distance between one riser and the next) and rise of staircases. The accepted dimensions allow for a sleeper rise of the staircase in houses than in flats and in turn, allow for a sleeper rise in flat than in public buildings. Compare Riser. Find>>

Tree root 126
Root of a tree. Roots can disrupt foundations and drainage by dewatering the subsoil. In the worst cases foundations can be undermined and require underpinning. With regard to drains, roots can cause drains to fracture and leak which can also disrupt foundations. Also, roots can enter the drain pipe via a small crack but once inside increase their diameter substantially, eventually growing and spreading in size to complete block the drain pipe. Willows, Poplars and Oaks are the most dangerous trees and should be located more than 25m from a building with vulnerable foundations.

Tree stump 134
Remains above ground of cut down tree. When a tree is removed because it is liable to cause damage to a property with vulnerable foundations consideration must be given to the risk of heave occurring once tree has been removed. If the tree to be removed is still healthy it may be prudent to remove it over, say three years by removing half the height in the first year and bringing the tree to ground level in the second and third year. If the tree is in its declining years it may be possible to remove it in one go. However, it is recommended that the advice of a tree surgeon is sought when removing trees from close to a building or drains.

Trench fill foundations 86
A narrow trench filled with concrete. Provided as alternative to concrete strip foundations where cost effective. Find>>

Tuck in of felt roofing into chase 61
The junction between top of felt upstand to a vertical abutment.Provided to help form a waterproof junction to upstand. The chase in the brickwork should be 32mm deep x 125mm high. The top edge of the upstand and underlay must be turned 25mm into the brickwork joint, bedded to the bottom of the chase and pointed to make waterproof. Find>>

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Support introduced under the existing foundations of a building. Provided to stabilise existing foundations which are suffering from subsidence for whatever reason, (See Subsidence) or to prevent settlement during adjacent excavation or other building works. Underpinning can deter some prospective purchasers and therefore restrict marketability and therefore adversely affect the value of the property. However, in an area of known “bad ground” an underpinned property (particular with long term and meaningful guarantees) should offer peace of mind and be less liable to future subsidence than an adjacent property which has not been underpinned. Find>>

Unsupported chimney stacks
Chimney breast left hanging when lower portion removed. Many chimney breasts have been removed in properties since the 1960’s and 70’s when open fires were unfashionable. In some instances no support at all was provided to support the remaining upper portion of the stack. In other instances bracketed support has been provided but in many instances this is inadequate. In such circumstances the overturning forces of the eccentric stack weight cause the wall and stack to slowly lean over. A structural engineer or chartered building surveyor should advise on and design an adequate means of support.

Upstand (to felt roofing) 64
See Flashing. Find>>

Upstand (to lead roofing) 142
The part of lead roofing turned up against a vertical surface.Provided to weatherproof a joint between a roof and a vertical surface and is then covered by an apron (See Apron)

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Valley gutter 15
The gutter to the intersection between two sloping pitched roof surfaces belonging to abutting roofs (known as the valley). Provided to make the angle at the valley waterproof. This detail can prove to be troublesome as the gutter lining (usually lead) sometimes fails or the pointing to the cut roof coverings at their junction with the guttering becomes defective or falls out. This can allow rainwater penetration into roof structure timbers which can lead to fungal decay of the roof timbers. Find>>

Vapour barrier/check (polythene) 58
A chemically inert water imperious sheeting. Provided to prevent the moist air which builds up through normal human activities escaping into walls and leading to dampness in the structural timbers. It is therefore important this barrier is not punctured or removed during any building works. Also as the damp air in the building will in the main find its final refuge in the roof space this must be well ventilation. Find>>

Vent cowl 30
A dome ventilation cap to a soil stack. Provided to prevent birds building nests in top of pipe which can lead to blockage. Find>>

Ventilation grills 128
See Air brick.

Vent light (top hung) 137
See Night vent.

Verge 2
The edge of a pitched roof at a gable. Usually pointed. If pointing becomes defective or falls out this can allow rainwater penetration into roof structure timbers which can lead to fungal decay of the roof timbers.

Verge board 23
See Barge board. Find>>

Vernier crack marker 182
Crack monitoring device. See Tell tale. Robust and cheap method of crack monitoring sufficiently accurate for most of low-rise building applications. Centre punched non-ferrous disks are epoxy glued to wall (in triangular shape - one on one side and two on the other side of crack) and distances between disks measured to establish extent and direction of movement (See Differential settlement crack). Find>>

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Wall flashing (to felt roofing) 64
See Flashing. Find>>

Wall hanger 75
See Joist hanger.

Wall plate 9, 117, 150
A horizontal timber bedded in mortar on top of wall. Provided to support ceiling joists, rafters, floor joists etc.

Wall string 159
A stair string fixed to the wall. Compare Outer string. Find>>

Wash hand basin 185
See Lavatory basin.

Waste pipe 195
A pipe which carried waste from a sanitary appliance which is used for washing, drinking or culinary purposes to a drain or soil stack. The discharge passed through a trap to prevent drain smells from backing up the waste pipe. Find>>

Waste bar 115
A galvanised steel flat fixed on edge into a groove in a sill. Provided to act as a barrier to the ingress of water. Find>>

Water table
The level of ground water on a site. The water table can vary seasonally or due to heavy rainfall or long dry spells. A dry basement floor can be dry when water table is low but be under water when it rises.

WC pan 191
A pan for the reception of body waste products. Forming part of a water closet. Usually of ceramic ware. The joint between the back of the pan to the soil pipe is prone to leakage. If leakage occurs this can lead to fungal decay of floor timbers. Find>>

Weather-board 114
A moulding fixed to the bottom of an external door. Provided to throw the water which has run down the face of the door clear of the threshold.

Weather-boarding 16
An external cladding consisting of horizontal boards nailed to the outside of a building. Provided as decorative finish with the upper board overlapping the lower one. Usually of timber or pvc. Find>>

Weathered fillet 25
See Fillet. Find>>

Weep hole 74
An aperture usually the joint width and a brick height through the outer skin of a cavity wall above a cavity tray at the head of a door or window opening. Provided to prevent the accumulation of water in the cavity. Find>>

Wet rot
A wood destroying fungus (Coniophora Puteana). Attacks wood and flourishes in wet conditions. Consists of a knobbly fruiting body with thread like strands. Wet rot can cause 40% weight loss (of affected timber) in four months and consequently significantly reduce strength of timber. Dies when timber moisture content falls below 43%. Therefore essential to cut off source of moisture and allow timber to dry out.

Window board 199 Find>>

Window head 198
The internal reveal to the soffit of a window opening. Usually plaster for decoration.

Wood roll 144
A round-topped piece of wood. Provided to form the longitudinal junction between sheets of metal in flexible metal roofing (shown as lead on drawing). The wood roll is fixed to the decking and the sheets of metal are dressed over it, lapped and folded into a welt.

Wood boring insect infestation
Insect infestation of timber Various types of beetle (eg common furniture, death watch, long horn, powder post, weavil). These can affect structural integrity of timber. Death watch and powder post beetle indicative of damp or fungal decay.

See Wood boring insect infestation.

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