NHBC Chapter 5.3, Approved Document H

Drainage Inspection Checklist

Below-ground drainage checks before backfill — gradients, bedding, joints, chambers, testing and the separation of foul and surface water.

20 checks · Reviewed 20 August 2026 by the ProPlot site team · How we write these guides

In short

The drainage inspection happens before backfill, with the runs open. The inspector checks pipe falls and gradients, bedding and surround material, chamber construction, cover levels and depth, connections to the sewer or treatment plant, and the results of the air or water test on each length.

Use it on site

Open trench at the drainage visit: depth of cover to the crown of the pipe, granular bed and surround, and a constant fall between access points. ProPlot original drawing, prepared from the Building Regulations Approved Documents and British Standards. Indicative only — build to the approved drawings for the plot.

Drainage is inspected open. Once the trenches are backfilled, a flat run, an unsupported joint or a cross-connection between foul and surface water is invisible until it causes a blockage, a flood or a failed adoption. That is why the warranty inspector and the adopting authority both want to see the pipework in the ground, jointed, on the correct bedding, before anything covers it.

The visit itself is largely arithmetic and observation: gradients against the drainage layout, invert levels at each chamber, bedding and surround material, benching and channel work inside chambers, and cover depth relative to whatever will run over the top. Where the run will be adopted under a section agreement, the water authority applies its own standards on top of Approved Document H, and a CCTV survey plus a successful air or water test is usually a condition of acceptance.

Work through the checks below before you call the inspection, and keep the test results and CCTV report on the plot file. Drainage evidence is the paperwork most often missing at CML, and reproducing it after the drive has been laid is expensive.

What happens at this visit

When it happens

When the below-ground runs are laid and jointed but before bedding is surrounded and backfilled. On adopted runs, book alongside the water authority inspection so the trench is only opened once.

Who inspects

Warranty provider inspector and building control for private drainage; the adopting water authority (or their agent) for anything offered for adoption under a Section 104 agreement.

If it fails

A failure means re-excavating a trench that may already be under a scaffold, a crane route or a plot access. Adoption refusals are worse: the run stays private, the management company inherits it, and the sale pack has to be redrawn.

How this visit is booked and recorded

Inspection type: Key Stage Inspection on sites where NHBC also carries out Building Control. Elsewhere it is inspected by your building control body and picked up in Risk Based Inspections.
Notice required: Minimum 24 hours’ notice, and the runs must still be open. Backfilling before the visit is the single most common reason drainage gets re-dug.
What it signs off: Supports the Building Regulations Part H sign-off and the adoption agreement for any sewer being offered for adoption.

What the inspector will ask for

Approved drainage layout with invert levels and falls
Air test and water test records for each run
CCTV survey where the adopting authority requires one
Section 104 / adoption correspondence for sewers being offered up
Soakaway percolation test results where used

Photograph these moments in time

Open trench showing bedding and surround material and depth
Each manhole with benching, cover level and step irons visible
Gauge reading during the air test with the run identifiable
Connections into the existing system before backfill
Lintels or protection where runs pass under or near foundations

Concealed work cannot be re-photographed later. Take these before the element is covered and file them against the plot.

Reportable Item hotspots at this stage

A Reportable Item (RI) is a defect the inspector records against the plot. NHBC weigh each one by its Damage Potential, and the score feeds your site's Construction Quality Review. These are the ones raised most often here:

Runs backfilled before inspection
Incorrect bedding material or insufficient surround
Falls outside the designed gradient

How Reportable Items and Quality Common Scoring work

The numbers for this stage

The measurable values most often argued about at the drainage visit, each traced to an openly published source. Take a tape to the ones that apply before you book.

Critical dimensions that apply at the drainage inspection
What	Value	Type
Backfill compaction protocolsTrench backfill must be well compacted in layers no deeper than 300mm to achieve stable groundObserve backfill operations to confirm compaction layers are within limits and mechanical compaction is not used too close to the pipe crown.	300 mm	Exact
Depth of cover to a buried drainBuried foul or surface water drain outside the building footprintTake levels over the pipe run before backfill, and again after landscaping — the depth that matters is the one under the finished surface.	600 mm under gardens and other areas not subject to vehicles; 900 mm under roads and driveways	Minimum
Distance from a soakaway to a buildingSurface water soakaway serving a dwellingSet out the soakaway position against the finished building line, not the excavation line, and record it on the as-built drainage plan.	5 m	Minimum
Drainage bed and manhole locationSubstructure drainage pipes must be laid on a suitable bed of granular material, such as 10mm pea gravel, to provide stable support and protect the pipes from ground movementConfirm drainage pipes are bedded on granular material and manhole positions avoid conflict with proposed external finishes.	10 mm	Exact
External drainage outlet and DPC clearanceExternal rainwater downpipes must discharge at least 150mm below the damp proof course (DPC) level, typically into a gulley or soakaway, to prevent moisture bridging across the DPC into the substructureVerify that all external drainage outlets are at least 150mm below the DPC and that no subfloor ventilators are positioned under doorways.	150 mm	Minimum
Gradient of a 100 mm foul drain100 mm foul drain serving at least one WCCheck invert levels at each end of the run with a level and staff before backfill. Falls that are too steep separate solids just as effectively as falls that are too shallow.	1 in 80 (steeper for runs with fewer appliances)	Minimum
Ground drainage pipe supportUnderground drainage pipes require proper support, either on a minimum 100mm deep granular bed or a carefully hand-trimmed trench bottomVerify that pipes are laid on specified granular bedding or a suitably prepared trench bottom, free from hard spots.	100 mm	Minimum
Height of a ventilating stack terminal above an openingOpen ventilating stack terminating at roof level or on an external wallCheck the terminal against every opening within 3 m, including rooflights and neighbouring plots on a terrace.	900 mm above the top of any opening within 3 m horizontally	Minimum
Minimum cover for mechanical compactionBefore mechanical compaction of trench backfill, a minimum of 150mm of material should be placed above the pipe to prevent direct damage.Verify that there is at least 150mm of cover over the pipe before any mechanical compaction is started.	150 mm	Minimum
Minimum WC connections per pipe diameterFor peak flows exceeding 1.0 litre per second, a 100mm diameter pipe serving multiple WCs should have a minimum of one WC connectionVerify that the installed pipe diameters are sufficient for the number of WCs and other appliances connected, based on flow calculations.	100 mm	Minimum
Pipe clearance for movementWhen a pipe passes through a structural element, it typically requires a minimum 50mm annular space around it to allow for movement and prevent stress transferEnsure that the specified minimum 50mm clear space is maintained around the pipe where it penetrates a structural element.	50 mm	Minimum
Spacing between drainage access pointsStraight run of buried drain between access pointsWalk the drain layout against the as-built drawing before covers are set to finished level. Confirm every change of direction and junction can be rodded.	45 m	Maximum

Browse the full critical dimensions library

The drainage checklist

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Falls, pipework and jointing

Verify pipe gradients meet Building Regulations (1:40 min for 100mm, 1:80 for 150mm) (AD H1)
AD H1
Check all joints are properly sealed — no visible displacement or open sockets (NHBC 5.3)
NHBC 5.3
Verify correct pipe diameter used for each run (100mm foul, 150mm combined) (AD H1)
AD H1
Confirm surface water and foul drains are correctly separated (no cross-connections) (AD H3)
AD H3
Check rainwater downpipe connections are properly trapped where connecting to foul drainage (AD H1)
AD H1

Bedding, cover and protection

Confirm bedding and surround material matches specification (pea gravel / concrete) (NHBC 5.3)
NHBC 5.3
Confirm minimum cover depth over pipes is met (600mm under gardens, 900mm under drives) (AD H1)
AD H1
Check that no drainage runs pass under load-bearing walls without lintel protection (AD H1)
AD H1
Verify ACO / linear channel drains are correctly laid to falls with sealed joints (NHBC 5.3)
NHBC 5.3

Chambers, gullies and access

Inspect manholes for correct benching, channels and smooth transitions (AD H1)
AD H1
Confirm all inspection chambers have correct cover strength for location (D400 for driveways) (BS EN 124)
BS EN 124
Verify back-drop manholes are correctly constructed with rest bend at base (NHBC 5.3)
NHBC 5.3
Check rodding eyes are accessible and positioned at changes of direction (AD H1)
AD H1
Confirm gullies are correctly trapped, bedded level and set to correct height (NHBC 5.3)
NHBC 5.3

Above-ground connections and stacks

Check SVPs are correctly positioned per layout drawing with fire collars where required (AD B)
AD B
Verify air admittance valves are accessible and above the flood level of the highest fitting (BS EN 12380)
BS EN 12380

Testing, surveys and adoption

Check water test or air test has been carried out on completed runs and passed (AD H1)
AD H1
Confirm CCTV survey completed and clear before backfill (report available on site) (SfA)
SfA
Check connections to adopted sewer are approved, inspected and properly benched (SfA)
SfA
Verify soakaway / attenuation tank size matches design calculations and is correctly sited (AD H3)
AD H3

Above and beyond: keeping the system clean before it is buried

Drainage snags are almost always contamination and damage during the build, not the original workmanship. No inspector will fail the visit on these — they are the difference between a plot that passes and a plot that hands over clean.

Cap every open pipe end and stack at the end of the day
One brick, one trowel of mortar or a lump of insulation in a buried run means excavating a finished driveway.
When: Every day until second fix connects.
Protect chambers and gullies from silt and washings
Mortar washings set hard in a gully trap and the whole fitting has to be dug out and replaced.
When: From installation through to the external works clean.
Bed and surround exactly as specified, then photograph it
Pea gravel bedding and surround depth is invisible after backfill and it is the first thing questioned when a run settles.
When: Before backfill, per run.
Cover manhole and inspection chamber openings with a solid, secured lid
Open chambers are the most common serious site injury on a plot and they collect rubbish.
When: Immediately on installation.
Keep the air test certificate and the CCTV survey with the plot record
A record you can produce at handover ends the adoption conversation quickly.
When: On completion of each run.
Protect finished falls from site traffic
Plant tracking across a shallow run flattens the fall and creates a standing water snag that only shows up in heavy rain.
When: Route site traffic away as soon as the run is backfilled.

Full inspection point register

51 inspection points that apply at the drainage stage, each written in our own words from openly published guidance, with how to check it on site and what counts as acceptable. Use the checklist above on the day and this register when you need to settle a detail.

Access for rodding every length
How to check
Trace each run on the as-laid drawing and confirm every length can be rodded from an access point at junctions, bends and gradient changes.
Acceptable when
Access at every junction, change of direction and change of gradient, and no straight run longer than 45 m between access points
See the measured value
Accurate setting out of drainage runs
How to check
Confirm that drainage run setting out aligns with design drawings and that any deviations have been formally approved and recorded.
Acceptable when
The setting out of drainage runs and depths must be accurately established from verified benchmarks. Any discrepancies encountered during excavation, such as unexpected ground conditions or dimensional variations, must be reported to the designer for modification and formally recorded.
Achieving drainage excavation levels
How to check
Verify trench depths, widths, and confirm that invert levels and gradients meet the design specification using surveying equipment.
Acceptable when
Excavation work for drainage must be meticulously executed to ensure that the designed invert levels and gradients are precisely achieved. Factors such as trench depth, width, and accurate setting out are critical to allow for proper flow and connection of drainage pipes.
Air or water test before backfill
How to check
Test each run before backfill and again after compaction, and record both results against the plot.
Acceptable when
Test passed and recorded before and after backfill, with no loss beyond the permitted limit
Bedding for below-ground drainage
How to check
Check that the correct depth and type of bedding material is laid and compacted in trenches before drainage pipes are installed.
Acceptable when
Below-ground drainage pipes must be laid on a suitable, stable bedding material, such as pea gravel or granular fill, to provide uniform support and prevent future settlement or damage. This bedding is installed prior to pipe laying to ensure the correct fall and protection of the pipework.
Capacity of extended private drainage systems
How to check
Verify that design calculations and investigations confirm the existing private drainage system can accommodate any extensions or increased capacity.
Acceptable when
When extending an existing private drainage system or increasing its capacity, a thorough assessment of the entire system's ability to cope with the increased flow is essential. This ensures that all components, from pipes to treatment facilities, remain adequate for the anticipated demand.
Depth of cover over the drain
How to check
Measure from the crown of the pipe to finished level at the shallowest point of each run, allowing for the final landscaping level.
Acceptable when
600 mm under gardens; 900 mm under roads and driveways, or protection provided where cover is less
See the measured value
Design of multi-home sewage treatment plants
How to check
Check that the design documentation for multi-home sewage treatment plants references and complies with BS EN 12566.
Acceptable when
Small sewage treatment works serving multiple dwellings must be designed and constructed in accordance with the relevant British and European standards. This ensures effective treatment of wastewater before discharge.
Drainage access points
How to check
Check that all planned access points are installed and correctly positioned as per the drainage layout drawing.
Acceptable when
To facilitate inspection, testing, and clearance of blockages, access points such as rodding eyes, access fittings, inspection chambers, or manholes must be strategically located throughout the drainage system. These points ensure that every section of the drainage run can be accessed for maintenance.
See the measured value
Drainage penetrations through external walls
How to check
Confirm that all drainage penetrations through external walls utilise robust ducts of an appropriate diameter, typically at least 50mm larger than the pipe.
Acceptable when
When drainage pipes pass through external walls, they must be accommodated within purpose-built ducts or sleeves that are significantly larger than the pipe itself. This allows for thermal movement of the pipe, prevents damage to the structure, and facilitates future maintenance or replacement.
Drainage pipe laying principles
How to check
Check that pipework follows the specified line and gradient, and that bedding material is correctly applied before backfilling.
Acceptable when
Underground drainage pipework must be installed precisely to the designed lines and gradients. Correct pipe bedding, sidefill, and backfill are crucial for long-term stability and performance.
Drainage pipe run design
How to check
Check that pipe runs are straight and direct, with bends only at designated access points, and ensure gradient consistency.
Acceptable when
Drainage pipe runs should be as straight as practically possible to maintain a self-cleansing velocity and minimise the risk of blockages. Changes in direction should primarily occur at inspection chambers or manholes to facilitate rodding and maintenance. Curves should be gentle enough to allow cleaning equipment to pass through.
Drainage pipe sizing
How to check
Verify that pipe diameters specified in the design match the installed pipes and are appropriate for the anticipated flow rates.
Acceptable when
Drainage pipes must be sized to accommodate the maximum expected peak flow from the connected appliances and rainfall. Groundwater drains and soakaways need sufficient capacity to handle normal weather conditions effectively. This ensures the system can cope without surcharge or flooding.
Drainage system compatibility
How to check
Review the drainage plans to ensure compatibility with the local public sewer system, verifying connections for both foul and surface water.
Acceptable when
The designed drainage system must be fully compatible with the existing main sewerage infrastructure. This includes systems with separate foul and surface water provisions, or hybrid systems where foul water connects to the main sewer while surface water uses alternative disposal methods like soakaways.
Drainage system design principles
How to check
Verify that the drainage design aligns with current regulations and considers all site-specific outfall conditions and capacities.
Acceptable when
Drainage systems must be designed according to relevant codes to effectively convey foul effluent and surface water to an appropriate outfall. Key considerations include connection rights, system compatibility, and the capacity of private or public sewers and treatment facilities.
Drainage system watertightness and testing
How to check
Ensure that appropriate tests (e.g., water or air tests) have been scheduled and witnessed for all sections of the drainage system prior to backfilling.
Acceptable when
All foul and surface water drainage systems must be constructed to be watertight. They are subject to inspection and testing as required by local authorities, sewerage undertakers, or warranty providers to confirm integrity before being put into service.
Drainage systems under buildings
How to check
Confirm that the design for drainage under buildings addresses ground conditions and movement potential, and that support is implemented accordingly.
Acceptable when
Drainage pipework installed beneath buildings must be specifically designed and supported to ensure its long-term integrity and performance, considering the anticipated lifespan of the building. Particular attention is required for support systems where ground movement is a risk, especially for pipework under suspended floors.
Drainage trench depth and refilling
How to check
Check that trench depths conform to design and that any over-excavated areas are refilled with approved materials to the correct level.
Acceptable when
Drainage trenches must be excavated precisely to the design-specified bottom levels. If a trench is over-excavated, it must be refilled to the correct level using suitable granular material or a lean concrete mix, such as GEN1 or ST ½.
Encasing pipes at movement joints
How to check
Verify that pipes passing through movement joints are correctly encased with compressible material and properly supported.
Acceptable when
Where drainage pipes pass through a building's movement joint, they must be encased in a compressible material and surrounded by concrete. This allows the pipe to accommodate differential movement without fracturing.
Field drain accommodation for treated effluent
How to check
Confirm that percolation tests have been completed and approved, and that the proposed field drain layout fits within the site.
Acceptable when
When disposing of treated effluent via field drains, the soil's percolation properties must be verified by testing. The design must ensure that the entire length of any specified field drains can be contained within the site's boundaries.
Flooding risk and drainage design
How to check
Verify that flood risk assessments have been conducted and flood authority advice integrated into drainage designs.
Acceptable when
Where a building site is identified as being at risk of flooding, the design of any drainage system must take this into account. Consultation with the relevant flood authority is essential to ensure appropriate mitigation measures are incorporated.
General principles for drainage system design
How to check
Review the drainage design to ensure it addresses ventilation, gas prevention measures, and correct siting of private treatment systems.
Acceptable when
Drainage systems must be designed and installed to prevent health hazards, which includes providing adequate ventilation to disperse foul air and preventing the ingress of gases into buildings. Careful consideration must also be given to the siting of septic tanks and cesspools, and the appropriate design of any pumped systems.
Gradient of the foul drain run
How to check
Level the invert at both ends of each run before backfill and calculate the actual fall against the length.
Acceptable when
Within the design range for the pipe size and appliances served — 1 in 80 for a 100 mm drain serving at least one WC
See the measured value
Granular bedding material specification
How to check
Check that the correct grade and size of granular bedding material is used, confirming compliance with BS EN 13242 and design specifications.
Acceptable when
The size and type of granular material used for pipe bedding must comply with relevant British Standards and be appropriate for the pipe diameter and flexibility. Recycled or secondary materials used for bedding or backfill must meet waste regulatory requirements.
Ground preparation for drainage pipe bedding
How to check
Ensure the trench bottom is free of hard points and that soft areas are properly excavated and backfilled with compacted suitable material.
Acceptable when
When preparing the trench bed for drainage pipes, any 'hard spots' must be removed to prevent stress concentrations on the pipe. Conversely, 'soft spots' must be excavated and refilled with suitable, well-compacted material to provide uniform support.
Groundwater drainage design principles
How to check
Verify that the groundwater drainage design includes an appropriate system for collecting and discharging subsurface water.
Acceptable when
Groundwater drainage systems are essential for managing excess sub-surface water and must be designed to effectively convey this water to a suitable outfall. The system should prevent waterlogging and protect foundations from hydrostatic pressure.
Groundwater drainage silt trap
How to check
Check for the correct installation of a silt trap on any groundwater drain connecting to a surface water drain.
Acceptable when
When groundwater drains connect into surface water drains, a silt trap must be incorporated on the groundwater side of the junction. This prevents the ingress of silt and debris into the surface water system, maintaining its efficiency.
Installation of flexible pipe joints
How to check
Verify that all flexible pipe joints are installed correctly as per the manufacturer's instructions.
Acceptable when
Flexible joints within a drainage system are critical for accommodating movement and must be installed strictly in accordance with the specific recommendations provided by the pipe manufacturer.
Manhole positioning and protection
How to check
Verify manhole positions align with planned landscaping and ensure they are adequately protected from construction traffic and debris.
Acceptable when
The placement of manholes and inspection chambers should be carefully planned to avoid being bisected by pathways or hard landscaping, which can compromise their structural integrity and accessibility. During the construction phase, these chambers require protection to prevent damage, contamination, or obstruction from debris.
Minimising risks in drainage systems
How to check
Verify that the drainage design addresses potential risks such as ground movement, access for maintenance, and prevention of blockages.
Acceptable when
Below-ground drainage systems must be designed and installed to minimise the risk of damage and blockages. Key considerations include ground stability, appropriate pipe runs, correct pipe sizing, suitable gradients, provision for access and connections, and protection from groundwater and flooding.
Percolation Value to Drainage Method
How to check
Verify that the proposed drainage method, such as field drains or underdrains, aligns with the site's recorded percolation test results.
Acceptable when
The determined percolation value of the ground directly influences the appropriate method for foul water drainage. Soils with specific percolation rates dictate whether field drains alone are sufficient, if underdrains are also required, or if the soil is entirely unsuitable for a sub-surface irrigation system.
Pipe bedding for uniform support
How to check
Confirm pipes are consistently supported by the correct bedding material for their full length as per design specifications.
Acceptable when
Drainage pipes must be firmly supported along their entire length to resist loads from overlying fill and traffic. The specified bedding material ensures uniform load distribution and prevents pipe damage.
Pre-backfill inspection and handover
How to check
Before backfilling, visually inspect all pipe runs, joints, and fittings for correct installation and damage; ensure any required tests are completed.
Acceptable when
Before drainage systems are backfilled, a thorough visual inspection is essential, and testing is strongly advised. At the point of handover, the entire drainage system must be fully operational, free from obstructions, and confirmed to be in good working order.
Preventing hazardous gas entry from drainage
How to check
Inspect the sealing arrangements where drainage pipes enter the building, particularly in areas identified with elevated hazardous gas risks.
Acceptable when
Where there is a risk of hazardous gases, such as radon or landfill gas, entering a building via the drainage system, specific sealing measures must be implemented. These precautions are typically applied at the point where drains penetrate the building envelope to create an effective barrier.
Private sewer capacity and design
How to check
Verify that private sewer designs conform to BS EN 752 and that the pipework installed matches the design capacity requirements.
Acceptable when
Private drainage systems must be designed and constructed to meet the requirements of BS EN 752. They must also possess sufficient capacity to handle the anticipated flow rates and effectively serve the properties connected.
Protecting drainage during construction
How to check
Ensure that protective measures, such as temporary barriers or suitable signage, are in place to prevent plant or vehicles from damaging newly laid drainage.
Acceptable when
Installed drainage systems must be protected from damage by subsequent construction activities. Heavy plant, vehicles, or significant loads should not be driven over or near unprotected drainage runs to prevent crushing or displacement of pipes. Any damaged drainage must be replaced.
Protection of buried drainage pipework
How to check
Check that all buried pipework has appropriate protection measures in place according to its location and surrounding elements.
Acceptable when
All buried drainage pipework must be adequately protected against potential damage. This includes careful consideration of pipes passing through structural elements, pipework laid beneath finished surfaces, and the provision for necessary movement joints.
Regulatory approval for drainage systems
How to check
Verify that design approval has been received from Building Control and the local sewerage undertaker for the drainage scheme.
Acceptable when
All below-ground drainage systems must comply with relevant technical requirements and obtain approval from the building control authority. Early consultation with local sewerage undertakers is crucial, especially if the system is to be adopted, as they may impose additional requirements for inspection and testing.
Septic Tank Drainage System Considerations
How to check
Confirm that all components of the septic tank drainage system, including outfall and soakaway, are designed and installed according to approved plans.
Acceptable when
The design of a septic tank system must address several critical factors for effective and compliant operation. These include ensuring suitable discharge routes, controlling flow velocity into the tank, and correctly designing soakaway systems, field drains, and any necessary underdrains.
Septic Tank Inlet Flow Control
How to check
Verify the drain gradient into the septic tank meets specifications and that rodding access is correctly installed at the connection.
Acceptable when
To prevent excessive turbulence within a septic tank, the flow velocity at the inlet should be managed. For smaller diameter drains, a gentler gradient is specified over a certain distance leading into the tank to achieve this. Provisions for rodding and cleaning must be included where the drain connects to the tank.

Most common reasons this visit fails

Flat spots between chambers

The run averages the right fall but dips in the middle where the trench bottom was not trimmed. Laser or boning rod every length, not just the ends.

High — usually means excavating a completed run.

Cross-connected downpipes

A rainwater pipe teed into the foul run is picked up on CCTV and on adoption. Colour-code the runs on site and check every connection back to the layout.

Medium to high depending on how much has been covered.

Cover level set before final levels

Chamber covers finish proud or sunk once the drive is laid. Set frames only when the finished surface level is confirmed.

High — adoption can be refused, which sits on the whole phase.

Backfilled before the test

Air testing after backfill tells you a run leaks but not where. Test each length as it is laid and record the result against the chamber reference.

Medium — but repeats across every plot if the detail is wrong.

Drainage inspection FAQs

Cap every open pipe end at the end of the day and keep chambers and gullies covered until the external works clean. Debris in a buried run means excavating a finished surface to clear it.

A minimum of 1:40 for a 100mm foul run serving fewer than about ten dwellings, and 1:80 for 150mm. Too steep is also a defect — solids can be left behind if the liquid runs away from them.

Either is acceptable under Approved Document H. Air testing is quicker and is what most sites use; water testing is more definitive and is sometimes required by the adopting authority. Record which you used, the pressure or head, and the duration.

Generally 900mm under a drive or trafficked area and 600mm under gardens and landscaping. Where you cannot achieve it, the pipe needs concrete protection or a structural slab designed by the engineer.

It can, but the crossing has to be designed — a lintel over the pipe, a flexible joint each side of the wall, and a sleeve through the masonry. An undesigned crossing is a routine Reportable Item.

Always before adoption, and it is good practice on private runs too. Do it before backfill so any defect is fixed in an open trench, and keep the report on the plot file for handover.

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Where this sits in the build

The key stage inspection sequence on a typical UK housing plot.

Other inspection stage checklists

Excavation & foundations

21 checks →

Basement / lower ground

28 checks →

Ground Floor & Slab

19 checks →

Superstructure

22 checks →

Timber Frame Erection

21 checks →

Roof

22 checks →

Windows and External Doors

24 checks →

Insulation & Airtightness

23 checks →

First Fix

28 checks →

Fire Stopping

22 checks →

Pre-Plaster

21 checks →

Second Fix

31 checks →

External Works & Pre-Handover

23 checks →

Pre-handover

22 checks →

General Quality

20 checks →

All key stage checklists

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