The five questions on every drainage instruction
Whatever the claim, the same five questions get you to a defensible recommendation:
- Who owns it? (Module 2 — public, private, shared, transferred?)
- What's the actual defect? (Module 3 — condition grade A/B/C, serviceable Y/N, root cause)
- What's the right repair? (Modules 3, 4, 5 — applying WRc Appendix D and Building Regs)
- What's the right scope? (Repair the insured peril vs upgrades / pre-existing conditions)
- Is the cost defensible? (Specification compliance + market norms + customer's policy)
The Catalyst recommendation template
| Section | What it answers | Anchored in |
|---|---|---|
| Property + system summary | What we found | Site visit + customer questionnaire |
| Ownership determination | Who pays | Module 2 / DRB Part 2 / 14-question test |
| Site investigation findings | What is wrong + cause | Module 3 / DRB Section 3.2-3.6 |
| Condition grading | A/B/C per drain section | Module 3 / DRB Section 3.3 / Table 3.4 |
| Recommended repair scope (insured peril) | What WE think is in scope | Modules 3-5 / DRB Section 3.5, 3.7 / Appendix D |
| Items outside insured peril | Pre-existing conditions, upgrades, GBR breaches | Module 4 / DRB Section 4.6, 4.9 / GBR rules |
| Cost validation | Specification-compliant pricing | Tables D.5/D.6/D.7 + market data |
| Recommendation | Approve / decline / negotiate | The above |
Case study — a worked example
Date: 12 March 2026
Property: 3-bed semi-detached, Cheshire (postcode CH4 8XX)
Property age: Built 1968. Connection to public foul sewer in highway. Surface water to soakaway in rear garden. Property is connected to United Utilities mains drainage; no private treatment system.
Customer: Mr & Mrs Reeves
Reported issue: Backing up of WC and shower in ground-floor en-suite. Reported intermittent over last 4 weeks; now persistent.
Insurer instruction: Investigate cause, recommend repair.
Step 1 — Who owns it?
Built 1968 → post-1937 so not a Section 20 sewer. Property is a single curtilage with a single drain. Connection to public sewer was in use well before 1 July 2011 → 2011 transfer caught the lateral drain (the section between the boundary and the public sewer in the highway). United Utilities is an English WaSC, so post-transfer the lateral drain is public.
- Foul drain inside the curtilage = private (Reeves' responsibility)
- Lateral drain (boundary → public sewer) = public (United Utilities)
- Public sewer in highway = public (United Utilities)
Implication: Investigation must distinguish where the defect is. If in the lateral drain, contact United Utilities first — unauthorised work is trespass. Catalyst's authority is for the in-curtilage portion only.
Step 2 — Site investigation
CCTV survey carried out 14 March 2026:
- Internal sanitary fittings drain to a single SVP at the rear of the property
- SVP joins the underground foul drain at the rear inspection chamber (IC1)
- From IC1 the drain runs under a paved patio for ~4 m to a second chamber (IC2) at the curtilage boundary
- From IC2 onwards = lateral drain (now public)
- Material: vitrified clay throughout the in-curtilage section
- Survey findings:
- IC1 → 2 m: clean, sound
- 2 m → 3.5 m: a circumferential crack at 3 m, with active infiltration
- 3.5 m → IC2: significant tree root ingress at the joint at 3.7 m, partially obstructing flow; clay pipe shows ~8 % deformation
Step 3 — Condition grading
- IC1 → 2 m: Grade A (sound)
- 2 m → 3.5 m: Grade B (cracks/fractures, some leakage, arching support intact)
- 3.5 m → IC2: Grade B (root ingress + 8 % deformation, <10 % rigid threshold so arching intact)
Serviceability: unserviceable (intermittent backing up = recurring blockage, plus active infiltration).
Step 4 — Identify cause of failure
- Tree root ingress at the joint at 3.7 m — sycamore tree at 4.5 m from drain centreline (within the 6 m DRB standoff but not breaching it). The garden has been undisturbed for 15+ years (no clearance per the <3 m / 7-year rule applies — sycamore is in the 6 m group, not the 4 m group)
- Beam failure at 3 m — circumferential crack consistent with localised soft ground below pipe (possibly washout from earlier joint leakage)
- Recurring blockage driven by both — flow narrowing from roots + grit collection at the cracked invert
Step 5 — Select repair technique
Per DRB Table 3.6 + 3.7:
- Both sections are Grade B + unserviceable + arching support intact → no-dig solution preferred
- The 1.5 m section between 2 m and 3.5 m: a CIPR patch with ≥100 mm overlap each side of the defect (so ~1.7 m patch)
- The 3.5 m to IC2 section: roots must be completely removed first (rodding/jetting/cutter, verified by post-clearance CCTV); then a CIPP part-length to seal the joint and exclude air. Annulus seal at IC2 end is essential to prevent regrowth.
- Total in-curtilage drain rehabilitation: ~3.5 m of CIPP/CIPR work
Step 6 — What is in scope?
- CCTV survey of in-curtilage drainage (already done)
- Root removal and verification
- CIPR patch on the cracked section (2 m → 3.5 m)
- CIPP part-length on the rooted joint section (3.5 m → IC2)
- Post-install CCTV inspection
- QC documentation pack
- The lateral drain section beyond IC2 is public — defects in that section are United Utilities' to investigate. Coordinate notification to UU; do not undertake repair without their authority.
- Any future tree management — discussed with the customer as ongoing maintenance, not a repair item
Step 7 — Cost validation
The contractor's quote should be measured against:
- Patch + part-length CIPP for ~3.5 m of 100 mm clay drain at modest depth (under patio)
- Carrier material, polyester resin (no PF host so no -10% reduction needed)
- Full QC pack delivered (resin batch, hardener batch, mix ratio, cure time)
- Post-install CCTV submitted for audit
- Reinstatement of the patio area (likely a single chamber lift only — no excavation needed)
If the contractor proposes excavation and replacement, challenge: arching support is intact, no-dig is preferred per Table 3.6, and reinstatement of the patio drives the cost up unnecessarily.
Step 8 — The recommendation
Approve no-dig repair (CIPR + CIPP part-length) on the in-curtilage drain, ~3.5 m total, with full QC pack. Notify United Utilities of any defects found in the lateral drain — investigation of that section is their responsibility. Advise customer separately on tree management as preventative maintenance.
When the case isn't this clean — five red flags
- Contractor proposes excavation when arching support is intact. Always check the deformation against the 10% / 20% threshold first.
- Off-mains tank replacement that is not like-for-like. Triggers Building Regs and GBR rules — and may pull drainage field upgrade into scope as a separate matter.
- Surface water connected to a private treatment system. Always dye-test gullies and rainwater pipes during off-mains investigations. If found, it's a GBR breach and must be separated.
- "Drainage field" that's actually a pit-soakaway. Non-compliant. Replacement is required regardless of tank condition.
- Pre-installation inspection was not done (e.g. tank empty, "couldn't see inlet/outlet"). The contractor's claim that they couldn't survey is itself a finding — proper investigation per DRB §4.5.3 was skipped.
Templates and tools
- 14-question responsibility test → Module 2 decision tree
- Drainage field calculator → Module 4
- Defect → repair decision matrix → Module 3 Table 3.6
- Standoff distance reference → Module 5 / DRB Appendix C
- CIPP wall thickness selector → Module 5 / Tables D.3, D.4
- Bedding & cover specs → Module 5 / Tables D.5, D.6, D.7
Knowledge check — Module 6 (Capstone)
Q1. A 1980 detached house in Lancashire (United Utilities). The lateral drain is blocked. The contractor wants to start work immediately. Catalyst's first action:
Q2. A 4-bedroom rural property has a septic tank from 1972 discharging directly to a stream. Contractor's quote: replace tank with new package STP. Catalyst's analysis:
Q3. CCTV shows a clay drain in the customer's garden with a circumferential crack but no leakage and no flow restriction. Reactive investigation. WRc says:
Q4. A 5-bedroom property in England with a septic tank. Field area required (Vp = 50, factor 0.25):
Q5. A subsidence claim. CCTV survey shows clay pipework. Drainage specialist did a leakage test which failed. Five-year-old vehicle access ramp passes over the line. Catalyst's recommendation:
Q6. A pitch fibre drain shows 25 % deformation on CCTV. Recommended approach:
Q7. The customer's policy responds to the insured peril of "accidental damage to drainage" (subject to standard terms). The investigation finds a long-standing root mass in a private drain that has caused gradual deterioration over a decade. Catalyst's view:
Q8. A property's drains pass under a neighbour's land. The customer asks if they have access rights for the repair. Catalyst's answer:
Q9. A contractor's quote includes "fully replaced drainage field" alongside a like-for-like septic tank replacement. The drainage field was previously a pit-soakaway (rubble). Catalyst's view:
Q10. Customer reports recurring foul drain blockages at a 1995-built property, England. CCTV: clay drain, no defects visible, gradient appears flat. Catalyst's diagnosis:
Q11. Building Regs Part H approval is required for:
Q12. A contractor invoice for a private drain repair in Cheshire arrives at £4,800 + VAT for replacing 2 m of clay drain in a back garden, depth ~0.7 m. The trench reinstatement is plain garden topsoil. Red flag because:
Q13. A customer has been told by the contractor that "we can't possibly know if the drain is leaking without a pressure test" before authorising repair. The drain is in a reactive (non-subsidence) investigation; there is no recurring blockage. Catalyst's view:
Q14. Catalyst's recommendation should always cite:
Q15. The single most important rule before any drainage investigation:
Six modules done. Time to take the final certification — 30 questions across all topics, 80% to pass, generates a personalised completion certificate.
Go to Certification →