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Glossary of Construction Terms - Sections N - H

Sections A - G >>
Sections O - S >>
Sections T - Z >>


Handrail 168
A rail at the top of a balustrade. Either horizontal or sloping and usually fixed about waist height. Can be fixed directly to wall. Find>>

Hardcore/hardcore bed 87, 121
Consolidated broken brick or gravel bed. Provided as level bed under next-to-earth concrete slab or oversite and pavings of other material. Usually blinded before concrete slab or pavings laid over. Find>>

Haunching 102
Concrete round the sides of drain pipe.Provided to support the pipe above the bedding concrete. Find>>

Header tank 46
See Central heating header tank.

Hearth 178
A non-combustible floor of a fire flue. Provided by means of a non-combustible slab (eg stone, concrete). Usually projects into room to protect floor from fire. Find>>

See Ground heave.

Herring bone strutting 152
Diagonal timber strutting fixed between floor joists. Provided to prevent the floor joists twisting as a result of shrinkage.High alumina cement concrete (HACC) A rapid hardening cement concrete.Used between 1950 and 1974. As a result of the ‘conversion’ of the HACC two school roofs containing HACC collapsed in 1973/74. However, after investigation if was found this only occurs in warm and moist conditions and very few buildings have been found to be unsafe and that in respect of residential property the Building Regulation Advisory Committee on HACC used the following advice:-

“Wholly residential property of less than 5 storeys containing HACC is exempt from examination by a qualified consulting engineer and properties confirming with the following conditions may be deemed to be safe. The buildings do not consist of more than four storeys. In the case of roofs of HACC construction (1) they are of joist and block composite construction, (2) they are not used for access, except for maintenance, (3) the spans do not exceed 6.5m clear (21”4”) in the case of standard joists having a depth of 7” or less (x7) and 8.5m clear (27.10”) in the case of similar beams having depths of 9” or 10” (x9 and x10). There is not persistent leakage or sustained heavy condensation.

Buildings which do not comply with these conditions should have the HACC examined by a suitably qualified consulting engineer and if it receives his approval may also be regarded as in safe structural condition”.

When inspecting properties built or altered between 1950 and 1974 and containing pre-cast concrete elements, valuers should make sure that the building satisfies the criteria for exemption. If in doubt, or if the building does request the vendor or his agent to provide evidence that the building does not contain HACC, or that if it does a structural engineer has inspected it and found it to be satisfactory.

Hip iron 50
A shaped galvanised or wrought iron strap. Fixed at the base of the hip rafter and provided to prevent the hip tiles slipping down the hip rafter.

Hipped end 38
The sloping triangular end to a hipped roof. Find>>

Hip iron 39

Hip rafter 39
A rafter forming a hip. Provided to form the edge (ie hip) of the meeting of two roof slopes. Find>>

Hip tile 37
A tile which covers the ends of the roof tiles which abut in a hip. Provided to make the angle at the hip waterproof. Find>>

Holderbat 100
A collar fixing for a pipe. Usually found in two parts capable of being clamped together and having one part with a projecting leg for fixing to a wall or soffit. Find>>

Hot water cylinder 171
A cylinder usually of copper.Provided for storing hot water. Modern copper cylinders now manufactured with foam lagging and this type preferable if replacing/renewing old cylinder. Where galvanised tanks present, because of their age replacement recommended (See Foam lagging and Lagging jacket). Find>>

Hygroscopic plaster
Plaster which absorbs moisture from the atmosphere. When a wall has suffered from rising dame this caused plaster to become hygroscopic. One hygroscopic, even if wall is effectively treated against rising dampness, plaster will invariably remain damp due to atmospheric moisture. Therefore, it is usual when damp proofing treatment is undertaken that replastering to approximately 1.33m is carried out using a waterproofed plaster.

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Immersion heater
An electric heating element. Designed to be installed in a water cylinder or tank. Find>>

Inspection chamber
A shallow manhole. Positioned on a drain at a change of direction or where branches join the main drain. Find>>

Inspection cover Find>>

Insulation (to timber framed wall) 57
Slab insulation fixed between timber frame members. Provided as thermal insulation in form of slab. Usually rockwool, glassfibre or similar. Find>>

Insulation board 68
A sheet material usually of low density. Provided to give thermal insulation to a flat roof. Laid on the roof joists before the roof decking to form what is called a warm roof.

Invert 106
The lowest point of the internal surface of a drain, sewer or channel in any cross section. Find>>

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Jack rafter
A short rafter. Provided between a hip rafter and the eaves, or between a valley rafter and the ridge. Find>>

Jamb 180
The vertical face of a wall opening which is the full thickness of the wall. Compare Reveal. Jamb can also refer to a vertical member of a window or door frame. Find>>

Joist hanger 75
A steel strap or stirrup. Provided to support the end of a joist by being either built into a wall or fixed to a trimmer joist.

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Keying in

The bonding of a new wall to an existing wall. If brickwork to brickwork then bonding usually every three alternate courses.  If brickwork to blockwork usually three courses of brickwork for one course of blockwork.

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Thermal insulation, usually insulating quilt enclosed in pvc for tanks and preformed for water pipes.Provided to prevent water in cold water storage or header tanks freezing.  The area beneath tank should not be insulated to allow heat from beneath to help prevent freezing. Water services pipes within the roof space should always be lagged to help prevent freezing. Find>>

Lagging jacket 173
A proprietary insulated jacket usually insulating quilt enclosed in pvc strapped and tied to hot water cylinder. Fitted to hot water cylinder (when not already foam lagged) to prevent excessive heat loss through wall of cylinder and consequently save energy and reduce fuel bills. (Compare Foam lagging). Find>>

Landing 167
A wide platform at the head of the stairs. Find>>

Downward movement of sloping ground resulting from the action of self weight stressed and imposed loadings exceeding the available strength of the ground. Landslip may be triggered by the application of superimposed loadings from buildings or may be induced by excavating into sloping ground with the result that material fails and moves down the slope.

Lap (of roof covering) 12
The amount by which courses of roof coverings overlap each other. Inadequate lap will allow rainwater penetration into roof structure which can lead to fungal decay of roof timbers. Penetration will occur from driving rain or capillary action particularly if shallow pitched is used. Find>>

Lath 158
A strip of softwood (usually about 25mm x 5mm). Fixed to timber stud partitions and ceilings and spaced with approximately 6mm gaps between to provide base for plaster to key itself to. Not used since about 1940 when plasterboard came into common use. Plaster on lath usually has life expectancy of between 50 - 70 years under normal conditions. Find>>

Lavatory basin 185
A sanitary appliance. Primarily for washing face, hands etc. Usually made of ceramic ware. Find>>

Leaded light 22
A window made up of small panes of glass set in lead. If a pane of glass in leaded light is broken the complete light will need to be removed for its replacement. In modern double glazing the leaded light is an effect created only by lead strips stuck onto surface of glass. Find>>

Lead roofing 141
A roof covered by lead sheets.Very durable but expensive roofing. Weak points tend to be rolls, drips and edges.

Lintel 67
A beam placed over a door or window opening. Provided to carry the weight of the wall over the opening. On occasions it may carry floor/roof members instead of, or as well as, a wall above.  Usually in form of reinforced concrete, RSJ or Catnic type (ie preformed metal). Find>>

Loft insulation 45
Thermal insulation usually laid between ceiling joints.Provided to prevent excessive heat loss through roof and consequently reduce fuel bills. Current Building Regulations require 200mm glass fibre quilt or similar. Alternative materials available but different thicknesses may be required to meet regulations. Grants should be available from Local Authorities if no insulation or insulation is less than regulation requirement. Adequate ventilation should be provided to the roof void to help prevent the build up of condensation which could damage the underside of the roof coverings and lead to fungal decay of roof timbers. Find>>

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Main drain run 104
The main run of drainage into which branch drains are connected and leads to main sewer. Possibility of some form of defect in drain very high in pre-1918 properties, and high in pre-1940 properties. In older properties normally clay with flexible joints which due to age and the flexible joints are less likely to suffer leakage. During 1950’s pitched fibre pipes were used, which are now proving particularly suspect to defect. If defects occur in drains close to foundations this can lead to structural problems. Modern drains in residential properties are normally PVCu which due to age and the flexible joints are less likely to suffer leakage. (Combination drain shown on illustration). Find>>

Manhole base 108
See Concrete manhole base.

Manhole (chamber) 110
A chamber constructed to give access to a drain or sewer.Usually constructed of brick or pre-cast concrete rings. Shallow manholes may be prefabricated in earthenware or plastic (Compare Inspection chamber).

Manhole cover 111
A removable access plate over a manhole.Generally of cast iron but lightweight covers of galvanised steel now in common usage but only where likely to be cross by lightweight traffic. Usually designed to be air tight. Should be replaced if broken.

Mixer tap 190
A tap in which separate supplies of hot and cold water are mixed. The outlet temperature of the water is usually controlled manually. However, with showers the temperature may be controlled thermostatically. Find>>

Moss & lichen
Vegetation growth indicative of damp usually on surface of wall or roof covering. Where on walls source of dampness should be investigated and necessary repairs carried out. However, dampness may have saturated wall and structural timbers internally opposite. On roof coverings it may have grown up and under coverings and may cause dampness in roof timbers. In either case this may lead to fungal decay of affected timber.

Mullion 135
A member that divides a door window vertically into lights. Not to be confused with glazing bars which divide lights into panes and can be vertical or horizontal. (Compare transoms).

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Newel post
A post in a flight of stairs. Provided to carry the ends of the outer string and handrail and supporting them at a change in direction. Find>>

Night vent (top hung) 137
A small top hung light in a casement window. Provided to give low level natural ventilation, particularly in bedrooms when they are occupied.

Noggin 187
Horizontal timber member between studs in timber framed wall. Provided to stiffen the studs in a timber stud partition. Find>>

Nosing 165
A usually rounded and overhanging edge to a stair tread. If nosing splits or becomes loose this can be potentially dangerous. Find>>

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