Glossary — Catalyst Training Academy

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A

Accidental Damage Drainage: An external cause acting on a pipe to make it inoperative or unserviceable. Insurers generally accept tree-root damage, vehicle pressure, ground movement and one-off blockages as Accidental Damage; pitch fibre delamination on its own and poor maintenance generally aren't.
Arboriculturist Subsidence: A tree expert who can identify species and age and predict the effect of a tree on nearby structures given known soil conditions. Distinct from a tree surgeon (prunes/fells). Their report is essential for both causation and foreseeability in a tree-root recovery action.
Atterberg Limits Subsidence: Water contents at which clay soil consistency changes — shrinkage limit, plastic limit, liquid limit. Plasticity Index (PI = LL − PL) classifies shrinkage potential. NHBC categorises clays with PI ≥ 50% as "high" shrinkage potential.

B

BRE Digest 251 Subsidence: Building Research Establishment classification of crack widths (Categories 0–5: Hairline / Fine / Moderate / Serious / Severe / Very Severe). Combined with the ISE 2nd Ed table to triage repair type.
BS 6297:2007 Off-mains: British Standard "Code of Practice for Design and Installation of Drainage Fields for Use in Wastewater Treatment". Annex H gives the percolation test method; mandates 0.20 sizing factor for treatment plant effluent vs 0.25 for septic tank effluent.
BS EN 12566 Off-mains: European standard for small wastewater treatment plants (≤ 50 PE). Compliance basis for septic tanks and STPs under General Binding Rules. CE marking confirms compliance.
Building Regs Part H Legal: Approved Document H of the Building Regulations — drainage and waste disposal. §1.34–1.40 cover percolation testing, the Vp 12–100 viable range, and drainage field sizing formulas.

C

Catch Pit Manhole Drainage: An empty chamber preceding an outfall to a watercourse, with inlet and outlet pipes set above the floor. Sediment carried by the system settles in the pit, where it can be periodically pumped out.
CCTV Survey Drainage: Camera inspection of underground drainage pipes. Standard tool for identifying defect type and location ahead of repair specification. Recorded against MSCC5 / WRc condition codes.
CDM Regulations Legal: Construction (Design and Management) Regulations. Apply when the client is the insurance company (e.g. for panel/Approved Contractors). Form F10 notification to HSE for projects above thresholds.
Cesspit / Cesspool Off-mains: A covered watertight tank with no outlet, used for receiving and storing sewage until pumped out. British Standards mandate a minimum 18 m³ capacity (~45 days for an average household).
Certificate of Structural Adequacy (CoSA) Subsidence: A professional opinion issued at completion of subsidence repairs that the works are appropriate to rectify the damage. NOT a warranty or guarantee. Transfer to a new owner needs the issuing expert's written permission and may require re-inspection.
CIPP Drainage: Cured-in-place pipe lining — a polyester or epoxy-resin sleeve inserted into the existing drain and cured to form a new pipe-within-a-pipe. Cold-cure polyester for short runs; warm/hot-cure for long runs; epoxy adheres to host pipe and adds structural strength.
Condition Grade A / B / C Drainage: WRc condition grading. A = structurally sound, slight cracks permitted, no repair needed. B = cracks/fractures observed but pipe still provides arching support, may have leakage. C = structurally unsound, total collapse/blockage likely. Subsidence investigations require B and C to be repaired; reactive investigations only require C.
Curtilage Drainage: The legal property boundary. The 2011 Private Sewer Transfer treats drains as private up to the curtilage boundary, public beyond.
Cyclical movement Subsidence: Seasonal opening and closing of cracks — open in dry summer (clay shrinks), close in wet winter (clay swells). Strong indicator of clay-shrinkage subsidence linked to vegetation.

D

Demec gauge Subsidence: Mechanical measuring device used with stainless steel monitoring studs to measure crack widths to ±0.1 mm. Industry standard for crack monitoring.
Desiccation Subsidence: The state where clay soil is significantly free of water — typically caused by tree-root water uptake. The trigger condition for clay-shrinkage subsidence.
Diminution in Market Value (DMV) Subsidence: Settlement option where the cost of repair approaches the property's market value or exceeds the sum insured. Three independent valuers agree the undamaged value; the property is sold and the shortfall settled.
Dip Pipes / H Pipes / T Pipes Off-mains: Vertical pipes within septic-tank chambers that isolate solids from the waste flow. T-pipes are single (90° T-piece + downward leg); H-pipes connect through an internal baffle wall. Failure usually means sludge entering the soakaway / drainage field.
DPC / DPM Subsidence: Damp-Proof Course (in walls — typically two courses above ground) and Damp-Proof Membrane (in floors — polythene under the slab). Cracks crossing the DPC into the foundation are a strong subsidence indicator.
Drain Drainage: A pipeline conveying foul sewage and/or surface water from a single property. Privately owned to the curtilage boundary. Compare with Sewer.
Drainage Field Off-mains: An infiltration system — perforated pipes in trenches that disperse treated effluent into the ground. Sized as P × Vp × 0.25 for septic tank effluent, or × 0.20 for STP effluent. Must be at least 1.2 m above the highest water level.

E

Eaves Spread Subsidence: Roof rafters without ties or restraint pushing the tops of walls outward. Often confused with subsidence but is a structural defect of the roof, not the foundation.

F

Foreseeability Legal: Element of a recovery action — damage is foreseeable if the tree owner knew or ought to have known there was a real risk if no preventative measures were taken. Local authorities have been deemed aware of the risks since the mid-1970s (Russell v Barnet); domestic owners generally cannot foresee unless put on notice (Greenwood v Portwood).
FOS Legal: Financial Ombudsman Service. Sorts complaints between consumers and regulated firms (insurers). Decision binding if accepted. Has clear positions on subsidence: stabilisation must be lasting (not patch-up); insurer continues beyond Sum Insured under "contract to repair"; tree work paid for if part of the repair, not if purely preventative.

G

General Binding Rules (GBR) Off-mains: Environment Agency rules governing small sewage discharges. Existing discharge (≤ 31/12/2014) and new discharge (from 01/01/2015) treated differently. Without a permit: max 2 m³/day to ground, 5 m³/day to surface water.
Gully Drainage: A small chamber where waters are "trapped" before flowing into the drainage system. The trapped water prevents smells and rats coming back up. Regular maintenance prevents blockage.

H

Heave Subsidence: The expansion of the ground beneath part or all of a building (upward movement). Most common cause: removal of trees from shrinkable clay, allowing the soil to re-wet and swell. Rule of thumb: removing a tree that predates the house may cause heave.
Helibar Subsidence: Helical stainless-steel rod system for crack stitching, reconnecting party walls, stabilising bowed walls into joist ends, and creating perimeter masonry beams. Beds in mortar joints with grout. Can sometimes avoid the need to underpin.
Highways Act 1980 Legal: Section 141: no tree to be planted within 15 ft of made-up carriageway centre. Section 96(7)(8): home owners may recover compensation for damage caused by Highway trees.
Hortlink 212 Subsidence: Research project showing that a 30–60% lateral / linear crown reduction on a tree achieves a 70–90% leaf-volume reduction. The basis for arboricultural mitigation prescriptions.

J

JCT contracts Subsidence: Joint Contracts Tribunal forms — Minor Works Form and Measured Term Form are most common for subsidence repair contracts. The Engineer typically acts as Contract Administrator.

L

Landslip Subsidence: The sudden movement of soil on a slope, or gradual creep over time. Most insurers' definitions exclude gradual creep. Possible causes: undercutting, water-course alteration, surcharge, retaining wall failure.
Lateral Drain Drainage: The portion of a drain from the curtilage boundary to the public sewer. Transferred to the sewerage undertaker under the 2011 Private Sewer Transfer, but only if connected to a public sewer.

M

MacKintosh Probe Subsidence: A lightweight portable penetrometer for soil bearing capacity. Standard practice: count the blows for every 75 mm of penetration.
Manhole / Inspection Chamber Drainage: A small covered chamber providing access to a drain or sewer for cleaning and CCTV inspection. Made of plastic, brick or concrete rings. Maintained by whoever is responsible for the outlet pipe.
Monitoring (crack / level) Subsidence: Periodic measurement of crack width or level changes to confirm cause and stability. 3-monthly is standard; weekly only for rapid movement (e.g. retaining walls). 3–6 months post drain repair, up to 12 months for tree-related cases. Level monitoring is mandatory when applying for a TPO felling/pruning consent.

N

Negligence Legal: Cause of action with four elements: duty of care, breach, causation, foreseeability. Subject to a 6-year limitation period (vs nuisance which is an ongoing tort and accrues a fresh cause each day).
NHBC Standards Ch 4.2 Subsidence: "Building Near Trees" — the industry standard for foundation depth design near trees on shrinkable clay. Often misused to justify underpinning depths; always reference the most current edition.
Non-Return Valve (NRV) Drainage: A valve that opens one way only, releasing waste from a property but preventing fluid surcharging back from a fully-charged main sewer. Limited storage during a closed event — surcharging within the property's own pipework is possible.
Nuisance (private) Legal: Cause of action requiring proprietary interest, causation and foreseeability. The most common basis for tree-root recovery actions. As an "ongoing tort", limitation accrues fresh each day for as long as the encroachment continues.

P

Party Wall etc Act 1996 Legal: Applies to work on existing party walls, building on the boundary, and excavation near a neighbour's building. Process: notice → 14 days to respond → silence = dispute → Surveyor as arbitrator → Award. Building Owner pays the Adjoining Owner's surveyor + structural engineer fees.
Pea Gravel Drainage: The standard bedding and surround material for modern flexible-jointed drains. Allows accommodation of ground movement and equal load distribution. Caution: a pea-gravel-filled trench acts as a land drain in clay — can de-water large areas.
Percolation Test Off-mains: Measures soil drainage rate. Three test holes 300×300×300 mm, filled and drained overnight, then refilled and timed for water level to fall from 75% full to 25% full. Vp = average time / 150 mm. Vp 12–100 = viable for drainage field; outside that range = specialist design.
Pitch Fibre Pipe Drainage: Wood-cellulose / coal-tar-pitch pipe, mass-produced 1950s–1972. Prone to delaminating and crushing into an oval. Pipes deformed < 20% can be re-rounded and lined; > 20% need replacement.
Plasticity Index (PI) Subsidence: Liquid Limit minus Plastic Limit. NHBC categorises clays: PI < 20 low, 20–40 medium, ≥ 40 high, ≥ 50 high (for foundation design). High-PI clays are most susceptible to shrinkage / swelling.

R

Raft Foundation Subsidence: A reinforced concrete slab the size of the building, designed to spread loads in very weak ground. Must be stiff enough to resist breaking under non-uniform settlement. Unreinforced versions are "oversite" slabs (typical of small garages).
Resin Injection Subsidence: Geopolymer resin injected into the ground to raise, re-level and re-support structures with subsidence. Avoids excavation. Best on granular soils with localised loss of bearing.
Rest Bend Drainage: Connects the vertical SVP to the near-horizontal underground drain. Typically 90° and located just below ground level.
RWP / SVP Drainage: Rainwater Pipe (gutter downpipe — surface water) and Soil Vent Pipe (above-ground vertical pipe taking foul waste away from toilet/bathroom; ventilates the drain). RWPs feed gullies or soakaways; SVPs end at a rest bend connecting to the underground foul drain.

S

Schedule of Rates Drainage: An agreed list of work and prices between client and contractor. The basis for transparent costing on every claim. Non-standard rate items must be substantiated before invoicing.
Septic Tank Off-mains: Underground anaerobic tank where solids settle to the bottom (sludge) and clarified liquid flows to a drainage field. Modern fibreglass / plastic tanks have central baffles; traditional brick/concrete used dip pipes / H pipes. Must be desludged at least annually.
Sewer Drainage: A pipeline conveying foul sewage and/or surface water from more than one property. Public sewers (owned + maintained by the Sewerage Undertaker) vs private sewers (per the deeds). Contrast with Drain.
Shear Vane Subsidence: Cruciform vane on a rod, rotated to measure soil shear strength. Standard classification (kPa): < 20 very soft · 20–40 soft · 40–75 firm · 75–150 stiff · > 150 very stiff.
Soakaway Drainage: A pit filled with stone / pea gravel, or a modular crate system, that disperses surface water (rainwater) into the ground. Never permitted for sewage effluent under GBR — must use a drainage field instead.
Stub Stack Drainage: An internal vent stack alternative for ground-floor toilets where a full SVP isn't viable. Limited use cases; subject to Building Regs Part H1 conditions.
Subsidence Subsidence: Vertical downward movement of a building foundation caused by loss of support of the site beneath, usually associated with change in subsoil volume (e.g. clay shrinkage from trees). Distinct from "settlement" (downward movement under building load — usually a policy exclusion).
Sum Insured Legal: The policy ceiling. FOS view: when an insurer chooses to repair, it has entered a "contract to repair" separate from the insurance contract; FOS is likely to require the insurer to continue beyond the Sum Insured for stabilisation and proper repair.

T

Tree Preservation Order (TPO) Legal: An order under the Tree Preservation (England) Regulations 2012 protecting specific trees. LPA confirms within 6 months or it lapses. Application for consent: 8-week determination, no reply = refusal. Penalties for cutting/destroying: up to £20k Magistrates' / unlimited Crown Court. Compensation for refusal where damage proven: 12 months to apply, 6 years to refer to Upper Tribunal Lands Chamber.
Trial Hole / Borehole Subsidence: Trial Hole = excavation to expose the foundation. Borehole = hand-augered hole to recover deeper soil and root samples. Standard subsidence investigation deliverable.
Trenchfill Subsidence: Modern foundation form: simple trench excavation filled with mass concrete (typically 900–1500 mm deep). Quicker and cheaper than building up substructure walls off a strip footing.

U

Underpinning Subsidence: Substructure reinforcement under an existing foundation. Traditional: mass concrete in 1.0–1.5 m hit-and-miss bays, dry-pack the 75–100 mm gap after 24h cure, 3-day wait between adjacent bays. Practical depth ~2 m. Pad & beam: intermittent pads at 2.5–3 m centres + spanning beam. Mini-piles: driven (loose soils) or augered (firm soils, deep stable strata).

V

Vp Off-mains: The percolation rate — average time in seconds for water to fall 1 mm in a standardised test hole. Vp 12–100 is the viable range for a drainage field. Below 12 = effluent reaches groundwater untreated. Above 100 = soil too slow → need watercourse discharge or raised mound.

W

Wear & Tear Drainage: Generally excluded from drainage cover. Clay pipes are inert and rarely "wear out" — most damage is from external factors. Cesspits / septic tanks / brick manholes with clear deterioration may be a Wear & Tear exclusion.
WRc Drain Repair Book Drainage: The Drainage Forum / Water Research Centre best-practice manual for domestic drainage repair. Covers ownership, defect classification, repair specifications, off-mains, tree roots and claims practice. The basis for the Academy's Drainage Claims course.

Z

Zone of Influence Subsidence: The volume of soil beneath a tree with lower moisture content than surrounding soil. The area where tree-related desiccation can cause foundation movement. Affected by topography (hard surfaces, retaining walls, etc).