Pipe Cover Depth Checker
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Pipe Cover Depth Checker
Check whether the depth of cover over a buried drain is within the safe minimum and maximum for the pipe material, size and location — and work the cover out from your ground and invert levels. Built on UK Building Regulations (Approved Document H1, Tables 8–10).
Is my cover depth OK?
Cover is the depth from finished ground level to the top (crown) of the pipe. The safe range depends on the pipe material, size and where it's laid (AD H Tables 8–10).
Work out the cover depth
Cover = ground level − pipe invert level − pipe outside diameter. Enter levels as depths below the surface, or as reduced levels (mAOD).
The cover is copied into the check tab. Cover is measured to the crown (top) of the pipe; depth to invert is measured to the bottom of the bore.
Limits of cover (Approved Document H)
Minimum – maximum cover for standard pipe strengths with Class B bedding (rigid) or Class S2 (plastic). Other strengths/bedding give different limits — see BS EN 1295.
| Size | Fields | Light roads | Main roads |
|---|---|---|---|
| 100 mm | 0.6–8+ m | 1.2–8+ m | 1.2–8 m |
| 225 mm | 0.6–5 m | 1.2–5 m | 1.2–4.5 m |
| 400 mm | 0.6–4.5 m | 1.2–4.5 m | 1.2–4 m |
| 600 mm | 0.6–4.5 m | 1.2–4.5 m | 1.2–4 m |
| Size | Fields | Light roads | Main roads |
|---|---|---|---|
| 300 mm | 0.6–3 m | 1.2–3 m | 1.2–2.5 m |
| 450 mm | 0.6–3.5 m | 1.2–3.5 m | 1.2–2.5 m |
| 600 mm | 0.6–3.5 m | 1.2–3.5 m | 1.2–3 m |
| Size | Fields | Light roads | Main roads |
|---|---|---|---|
| 100–300 mm | 0.6–7 m | 0.9–7 m | 0.9–7 m |
Minimum depth in roads is set to 1.2 m for rigid pipes irrespective of strength. For drains <1.5 m deep with a risk of adjacent excavation (loss of side support), a special calculation to BS EN 1295 is needed. Below the minimum, protect the pipe with a reinforced concrete cover slab over a flexible filler and ≥75 mm of granular material (AD H 2.44). Above the maximum, use a stronger pipe class or higher bedding factor.
This pipe cover depth calculator checks whether the depth of cover over a buried drain is within the safe minimum and maximum for the pipe material, size and location, and works the cover out from your ground and invert levels. It follows Approved Document H1 (Tables 8 to 10). See Approved Document H for the full guidance.
Is my cover depth OK?
Cover is the depth from finished ground level to the top (crown) of the pipe. Too little and the pipe can be crushed by traffic; too much and the load from deep fill becomes the problem. The safe range depends on the pipe material — rigid clay or concrete versus flexible plastic — its size, and where it is laid. Enter those and the calculator returns the permitted cover range and a pass or fail.
Working cover out from levels
If you are not sure of the cover, enter the finished ground level and the pipe invert level (as depths below the surface or as reduced levels) and the pipe diameter, and the calculator works out the cover for you — cover = ground level minus invert level minus pipe outside diameter.
What to do when cover is too shallow or too deep
Where cover is below the minimum, the pipe usually needs protection — a concrete surround or a bridging slab. Where it is too deep for the pipe class, a stronger pipe or special bedding may be required. The checker flags which case you are in so you can detail it correctly.
Further reading: drainage information needed for planning permission · foul, surface and combined sewers explained · Approved Document H.
Frequently asked questions
It depends on the pipe and location. Under fields or gardens flexible pipes can have less cover than under a road; Approved Document H Tables 8 to 10 set the limits, which the checker applies.
It risks being cracked or deformed by surface loads. The usual fix is a concrete surround or a bridging slab to spread the load.
Cover is from finished ground level to the crown (top) of the pipe, not to the invert. The checker can work it out from your levels if you are unsure.
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