Structural repair glossary

Words you are likely to meet in an engineer’s report, an insurer’s letter or a quote, explained in plain English.

Beam and base

Beam and base is an underpinning method in which a reinforced concrete beam is formed under or alongside the existing foundation and carried on mass-concrete bases at intervals. The beam spreads the building’s load onto the bases, which sit on firmer ground deeper down. Underpinning

Bed joint

A bed joint is the horizontal layer of mortar between two courses of bricks or blocks. Crack stitching bars and remedial ties are usually set into bed joints, because the mortar can be cut out and refilled without damaging the bricks either side. Crack stitching

Betterment

Betterment is any improvement beyond putting a property back to its condition before the damage, such as an upgraded finish or extra work the claim did not need. Insurers usually pay only to reinstate, so betterment is normally paid for by the owner. Subsidence insurance claim repairs

BRE Digest 251

BRE Digest 251 is a Building Research Establishment guide that grades visible damage to buildings in categories 0 to 5, mainly by typical crack width, from negligible (under 0.1 mm) to very severe (usually over 25 mm). It is a guide, not a diagnosis. Structural crack repairs

Building control

Building control is the service that checks building work meets the Building Regulations, provided by your council or a private building control body in England and Wales, and by councils in Northern Ireland. Structural work such as underpinning needs its approval and inspections. Underpinning

Building warrant

A building warrant is the permission needed in Scotland before most structural building work starts, granted by the local authority verifier. When the work is finished, a completion certificate is submitted and accepted to confirm the work meets the building standards. Underpinning

Carbonation

Carbonation is the slow reaction between carbon dioxide in the air and concrete, which lowers the concrete’s alkalinity from the surface inward. When it reaches the steel reinforcement, the steel loses its natural protection and can start to rust, which leads to spalling. Concrete repairs

Certificate of structural adequacy

A certificate of structural adequacy is a document from a structural engineer stating that, in their opinion, repairs have been completed satisfactorily and the building is structurally adequate for its use. It is often issued at the end of a subsidence claim, and buyers and lenders commonly ask for it. Subsidence insurance claim repairs

Crack monitoring

Crack monitoring is recording the width of cracks at regular intervals, usually over 6 to 12 months, to find out whether movement is continuing and whether it follows the seasons. The results help decide whether a crack can be repaired or needs further investigation. Structural surveys and crack monitoring

Crack stitching

Crack stitching is a repair that bonds cracked masonry back together by grouting stainless steel helical bars into slots cut across the crack in the mortar joints. The crack is then filled and repointed. It is done once whatever caused the crack has stopped. Crack stitching

Flaunching

Flaunching is the sloping bed of mortar on top of a chimney stack that holds the chimney pots in place and sheds rainwater off the top. When it cracks or breaks up, water gets into the stack and the pots can work loose. Chimney stack repairs

Heave

Heave is upward movement of the ground under a building, usually when clay soil swells as it takes up water. It can follow the removal of a large tree or a leaking drain saturating the ground, and it cracks walls in a similar way to subsidence. Subsidence repairs

Helical bar

A helical bar is a thin stainless steel bar twisted into a spiral, grouted into slots cut in masonry to bridge cracks or tie sections of wall together. The twisted profile grips the grout along its whole length, so the masonry acts as one piece again. Crack stitching

Landslip

Landslip is the downward movement of sloping ground, where soil or rock slides down a slope and can take foundations, garden walls or paths with it. Buildings policies usually cover landslip alongside subsidence and heave, subject to their terms. Retaining wall repairs

Lateral restraint

Lateral restraint is the sideways support a wall gets from the floors, roof and cross walls connected to it, which stops it leaning or bowing. Where that connection is missing, steel restraint straps or remedial ties are fitted to tie the wall back to the floor or roof timbers. Bowing wall repairs

Level monitoring

Level monitoring is measuring the height of fixed points on a building with precise surveying equipment at intervals over time. It shows whether the foundations are still rising or falling, and is often used alongside crack monitoring or after ground stabilisation. Resin injection ground stabilisation

Lintel

A lintel is a beam over a window or door opening that carries the wall above it. Older lintels may be timber, stone or reinforced concrete, and when they rot, crack or corrode, the brickwork above usually cracks or starts to drop. Lintel replacement

London Clay

London Clay is a high-plasticity shrinkable clay that underlies much of London and the South East, the part of the UK most susceptible to clay-related subsidence. It shrinks markedly in dry summers, especially near trees, and swells again when it rewets. Subsidence repairs

Loss adjuster

A loss adjuster is a claims specialist appointed by an insurer to investigate a claim, confirm whether it is covered and manage the repair. In subsidence claims they often bring in an engineer and arrange drain checks, tree investigations and monitoring. Subsidence insurance claim repairs

Mass-concrete underpinning

Mass-concrete underpinning is the traditional method of underpinning, where short sections, often called pins, are dug beneath the existing foundation one at a time in a set sequence and filled with concrete. The foundation then bears on firmer ground deeper down. Underpinning

Mini-piling

Mini-piling is a foundation repair in which small-diameter piles are driven or drilled deep into the ground to carry a building’s load past weak or shrinkable soil. The piles are linked to the walls by a reinforced concrete beam, and it suits sites where firm ground is too deep to dig to. Underpinning

Mining Remediation Authority

The Mining Remediation Authority, formerly called the Coal Authority, is the government body that handles claims for damage from past coal mining where it is responsible, and holds records of old coal workings. Where another operator is responsible, the claim goes to them instead. Mining subsidence repairs

Needle

A needle is a short steel or timber beam passed through a hole in a wall and propped on both sides, so it carries the masonry above while the wall, lintel or foundation below is repaired. Needles are usually temporary and removed once the repair is complete. Lintel replacement

Padstone

A padstone is a solid block of concrete, stone or engineering brick set under the end of a lintel or beam to spread its load into the wall below. Without one, a heavy load can crush the brickwork it sits on. Lintel replacement

Party wall

A party wall is a wall shared by two properties, such as the wall between semi-detached or terraced houses. In England and Wales, the Party Wall etc. Act 1996 sets out the notice needed for work to it, and garden walls astride the boundary are covered as party fence walls. Boundary and garden wall repairs

Purlin

A purlin is a horizontal timber beam running along the length of a roof slope, under the rafters, that supports them part-way between the eaves and the ridge. Purlins are usually propped by struts down to a load-bearing wall below. Roof structure repairs

Resin injection

Resin injection is a ground stabilisation method in which an expanding resin is injected through small tubes into the soil beneath a foundation. The resin fills voids and compacts weak ground, can lift a foundation slightly, and is usually followed by level monitoring. Resin injection ground stabilisation

Roof spread

Roof spread is outward movement at the feet of a roof’s rafters when they are not tied together firmly enough. It pushes the tops of the walls outward and lets the ridge sag, and it is resisted by adding ties, collars or steel straps. Roof structure repairs

Settlement

Settlement is the downward movement of a building as the ground beneath compresses under its weight, mostly in the first few years after construction. It usually slows and stops, is different from subsidence, and is normally excluded from buildings insurance. Structural crack repairs

Shrinkable clay

Shrinkable clay is clay soil that shrinks noticeably when it dries and swells when it gets wet. Trees, dry summers and leaking drains change its moisture, moving foundations built on it. London, Oxford and Gault clays are among the most affected in the UK. Subsidence repairs

Sistering

Sistering is strengthening a damaged or weak timber joist or rafter by fixing a new length of timber alongside it, so the two share the load. It avoids removing the original member and is usually quicker and less disruptive than replacement. Floor joist repairs

Sleeper wall

A sleeper wall is a low wall, usually of brick, built under a suspended timber ground floor to support the joists part-way across the room. It is built with gaps so air can move through the void, and should have a damp-proof course under the timber. Floor joist repairs

Spalling

Spalling is the breaking away of flakes or chunks from the surface of concrete, brick or stone. In reinforced concrete it is usually caused by the steel inside rusting and expanding, while in brickwork it is more often frost damage or an unsuitable mortar. Concrete repairs

Subsidence

Subsidence is downward movement of the ground supporting a building’s foundations, not caused by the weight of the building itself. In the UK it is most often caused by shrinkable clay drying out near trees, leaking drains softening or washing out the soil, or past mining. Subsidence repairs

Sulphate attack

Sulphate attack is chemical damage to mortar or concrete, where sulphates from soil, groundwater, hardcore, bricks or flue gases react with the cement and expand. It can make mortar crumble, push concrete floor slabs upward and cause chimney stacks to lean. Concrete repairs

Tell-tale

A tell-tale is a small gauge fixed across a crack, usually two overlapping plates with a grid and cross-hairs, that shows whether the crack is opening, closing or shearing over time. Readings are taken at intervals and recorded with the date. Structural surveys and crack monitoring

Underpinning

Underpinning is strengthening a building’s foundations by extending them deeper or wider to reach firmer ground, or by transferring the load onto piles. It is building work that needs building control approval, and it is used only where the ground will not otherwise stabilise. Underpinning

Voussoir

A voussoir is one of the wedge-shaped bricks or stones that make up an arch, locking together to pass the load around the curve to each side. The central voussoir at the top is called the keystone, and if the arch spreads, voussoirs can slip and drop. Brick arch repairs

Wall tie

A wall tie is a metal tie that bridges the gap in a cavity wall, built into both the inner and outer leaves to hold them together. Older steel ties can rust, swell and crack the outer brickwork, and are then replaced with stainless remedial ties. Wall tie replacement

Weep hole

A weep hole is a small opening near the base of a wall that lets trapped water drain out. In retaining walls, weep holes relieve the water pressure behind the wall, and in cavity walls they let water escape from above trays and lintels. Retaining wall repairs