Certifying a subcontractor's defective sanitary plumbing under pressure
You are the certifying plumber on a $2.8 million childcare centre fit-out. The sanitary plumbing subcontractor has installed 12 hand basins, four toilets, a kitchen sink and a 25 m length of 100 mm PVC building drain at a fall of 1:120. The contract makes you responsible for certifying the sanitary plumbing before handover. During your inspection you find the drain gradient, a 50 mm basin waste run of 8 m with no relief vent, and no grease trap on the kitchen sink. The subcontractor says the council inspector passed the rough-in and asks you to sign the certificate because the children start next week. The main contractor threatens to withhold your fee.
1. Assess the defects and decide your immediate actions.
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The defects are not cosmetic. A 100 mm drain at 1:120 is flatter than the normally required minimum of about 1:60, so it has insufficient self-cleansing velocity and is likely to block. The 8 m of 50 mm basin waste without relief venting is at risk of trap-seal siphonage, which can allow sewer gases into the childcare area. The missing grease trap on the kitchen sink is a compliance and maintenance problem, and grease discharge could clog the drain.
My immediate action would be to stop covering or commissioning the affected work, issue a written non-conformance with photographs and levels, and require the subcontractor to propose rectification. I would not sign the certificate. I would notify the main contractor and client in writing that certification is withheld pending rectification and re-inspection. If the drain is already covered, I would require it to be exposed or CCTV-inspected and re-laid if the grade cannot be verified.
2. How should you manage the certification, contractual and regulatory communication?
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Certification is a technical statement that the work complies; it is not a favour to the main contractor. I would set out the specific non-compliances, the required rectification, the inspection hold points and the tests needed: laser or survey levels for the drain, a water test, vent verification and confirmation of the grease trap installation.
I would record that the council rough-in inspection does not relieve the certifier of the duty to verify compliance, and I would notify the council if the work is notifiable or if a defective installation has been covered. Contractually, I would keep my fee claim separate from the certification decision and put the main contractor on notice that withholding a fee does not make non-compliant work compliant. If the contractor directs me to certify anyway, I would decline in writing and retain the records.
3. What mentoring and quality assurance actions would prevent recurrence?
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I would treat this as a system failure as well as a workmanship failure. Before the next stage, I would hold a toolbox talk with the subcontractor and apprentices covering minimum drain grades, venting of long fixture branches, grease trap requirements and the consequences of covering work before inspection. I would introduce a pre-cover checklist signed by the installer and supervisor, with laser-level readings recorded for every drain run.
I would set hold points for inspection before concrete or framing is closed in, and require the subcontractor to provide a producer statement for each rectified section. I would also mentor the site supervisor on how to challenge a passed rough-in when the finished work is defective. The aim is not blame; it is a verifiable quality process so that the next childcare fit-out does not rely on last-minute pressure to certify.