Building Control Inspection: Drainage and Oversite
PremiumTwo BCO inspections stand between your foundations and the floor slab. Here's what the inspector checks at the drainage and oversite stages, how to prepare, and what happens if you cover the work too early.
Do this first:
After your foundation inspection passes, there's a temptation to push ahead. Foundations are in, concrete is cured, blockwork is rising. The momentum feels good.
But between that approved foundation and the floor slab, building control needs to see your site twice more. Both inspections gate work that cannot be undone.
Cover your drainage before the BCO has seen it and you're digging up trenches. Pour your oversite concrete before the BCO has checked the DPM and insulation and you could be breaking out a slab with a jackhammer. These are not theoretical risks. They happen on domestic extensions regularly, and they add thousands to the final bill.
The drainage inspection and the oversite inspection are two separate stages. They happen at different points in the build programme (sometimes days apart, sometimes weeks) and both must pass before concrete goes down for the floor slab.
Your foundation inspection must have passed before reaching these stages. You should also have your drainage fully installed before requesting the drainage inspection. If your foundations aren't signed off, nothing that follows counts.
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