The Defective New-Build Drainage
You are instructed by a private client who purchased a new-build house 14 months ago. Since occupation, the rear garden has flooded twice after heavy rain, and a foul odour has appeared near the rear patio. The client has had a CCTV drain survey done, which shows a partially collapsed clay drainage run under the patio and a section of drainage that appears to have been laid at a fall of approximately 1:200 in the wrong direction over a 12 m length. The house builder's NHBC warranty is in place. The builder's customer care team has offered to 'jet the drain and re-lay the patio'. The client wants to know whether to accept, and whether they can claim for the garden flooding. The original site investigation report is not in the client's possession.
1. Analyse the drainage defect and explain why the builder's proposed remedy is inadequate.
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The CCTV findings indicate two distinct defects: a structural collapse of a clay run under the patio, and a reverse fall over 12 m. A reverse fall means the drain cannot achieve self-cleansing velocity; solids will settle, the pipe will silt, and the odour is consistent with trapped foul water and possibly a surcharged or leaking joint. Jet-cleaning treats the symptom (silt) but not the cause (the fall and the collapse). Re-laying the patio without addressing the drainage beneath it will simply bury the defect again. The correct remedy is to excavate and re-lay the affected run to correct falls, with a proper granular surround and inspection chambers, and to verify by CCTV on completion. The builder's offer is a cosmetic fix that will fail again and may leave the client with a defect that becomes their responsibility after the warranty period.
2. Advise the client on the contractual and warranty routes available, and the evidence they need to gather.
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Routes: (1) NHBC warranty - the client should notify NHBC formally and in writing, providing the CCTV survey and a description of the defects; NHBC has its own resolution and claims process. (2) Consumer protection / statutory rights - the client may have a claim against the builder under the Consumer Rights Act 2015 (goods and services) and/or the Defective Premises Act 1972, subject to limitation. (3) Contract - the original building contract terms and any collateral warranty should be reviewed. Evidence to gather: the CCTV survey with a written report and drawings showing the location and fall of the defective run; dated photographs of the flooding and odour; a diary of events and correspondence with the builder; the NHBC certificate and policy documents; and, if possible, the site investigation and drainage design drawings - the client should request these from the builder and the local authority building control file. A trial hole to confirm the fall and pipe condition would strengthen the case. The client should not accept the builder's offer in writing without reserving their rights.
3. What would you recommend the client do about the missing site investigation report, and why does it matter?
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The site investigation report matters because it may show ground conditions (e.g. high water table, shrinkable clay, or made ground) that explain the collapse and could indicate whether the drainage design was appropriate. It may also be relevant to whether the builder complied with the design. The client should request it from: the builder, the local authority building control department (which may hold it on the file), the NHBC, and any consulting engineer named on the drawings. If it cannot be obtained, the client should commission a new site investigation (at least a couple of trial pits and a soakaway test) to establish ground conditions and to inform the remedial design. This is not just procedural - the remedial design (pipe bedding, surround, and whether a pump or alternative drainage is needed) depends on it, and the absence of the report weakens any claim that the builder's design was fit for purpose.