The three ways this job arrives
A heating engineer stands in the kitchen with a flow cup under the cold tap, watches it fill at nine litres a minute, and declines to hang the combi he was booked to fit. That is the first way. The second is a kitchen strip-out that exposes a soft grey pipe with a swelling at the joint and a scrape that goes silver, and the conversation stops being about worktops. The third is slower and less dramatic: a fifteen millimetre galvanised iron riser that has been weeping rust at the elbow behind the washing machine for two years and has finally reached the point where nobody wants to put a spanner on it.
All three end in the same place, which is a machine on the drive and a narrow trench from the boundary to the front wall. What separates them is only how much of the internal pipework goes at the same time. The heating job needs the outside run and probably the first three metres inside. The lead job needs everything lead, inside and out, or it is not really finished. The iron job needs the riser and whatever the riser has been quietly feeding rust into for a decade.
One structural fact governs the whole thing and it is worth stating in the language of the appointment diary rather than the language of ownership. From the street main to the boundary is the undertaker's pipe and the undertaker's van; from the boundary to the internal stop tap is the property owner's pipe and the property owner's digger. Two organisations, one hole in the ground, and only one of them can be booked at short notice. Everything below is arranged around getting those two to meet on the same morning.
Booking the connection before booking the digger
Apply first. Every water undertaker in England and Wales has an application route for a replacement or upgraded supply, most handle it as a form and a fixed quotation, and many run a lead replacement scheme that will renew their half at no cost or at reduced cost when the owner renews theirs at the same time. That last point is worth reading twice, because it is the difference between a new twenty-five millimetre plastic supply pipe teed onto a surviving lead communication pipe — which improves the job by about a third — and a genuinely new service from the main. The duty to make the connection sits with the undertaker under the Water Industry Act 1991, and the price and the lead time are theirs to set. Six to eight weeks is ordinary. Ten days is not.
The application also collects things the design needs. Ask, in the same conversation, whether the property will be metered as a condition of the new connection and where the meter will sit, what size communication pipe is being offered, whether the street main is programmed for replacement, and precisely what the connection crew expects to find when they arrive. That last answer is the one to write down. The pipe has to be laid, capped, pressure tested and left with the trench open at the boundary end, and a crew that arrives to find a backfilled trench or the wrong material will leave and rebook.
- Apply to the undertaker for the replacement supply and ask on the same call whether a lead replacement scheme applies to the property.
- Get the offered communication pipe size and the meter position in writing, because both change where the owner's pipe has to terminate.
- Confirm the notifiable work list with the undertaker before anything is ordered, since the Water Supply (Water Fittings) Regulations 1999 make some of this job notifiable before it starts rather than after.
- Book the connection date, then work backwards to the excavation date, allowing a clear week for the test, flush and disinfection between them.
- Have the underground services located and marked, and any trial holes dug by hand, before the machine is delivered rather than on the morning it arrives.
- Order the pipe in a single coil long enough for the whole surveyed route with slack at both ends, and check the coil on delivery for the Kitemark and the batch date.
Walking the route before the trench is priced
The route is a survey, not a straight line, and it is decided on foot with a tape and a locator. A mature tree gets a wide berth in both directions: the roots will damage the trench work and the trench work will damage the roots, and neither party recovers well. A driveway is a decision about whether to open it, duct under it, or go round it. Existing services get located with a cable avoidance tool and confirmed by hand-dug trial holes, in the sequence the HSE sets out in HSG47, and the incoming electricity service is the one that has never once been where the drawing said. Nothing about this is optional on a domestic plot: a service trench is shallow enough to feel harmless and a struck supply cable is not.
Then measure what you actually surveyed. The number that matters to the pipe is not the plan dimension from the boundary box to the front wall; it is the developed length — the trench route with its bends in it, plus the drop from ground level down to the formation at the boundary, plus the rise up through the building entry, plus the slack coiled at each end so the connection crew and the internal plumber both have something to work with. On an ordinary front garden that turns twenty-two metres of plan into thirty-something metres of pipe, and it is the thirty-something that friction is charged on.
Run that length through the friction arithmetic before the trench is priced, because going round the lime tree is a decision with a number attached to it. Take a thirty-four metre surveyed route at twenty-five litres a minute, which is a shower and a bath tap together on a house that is not being asked to do anything heroic. Through twenty-five millimetre MDPE, which has a bore of about 20.4 mm, that costs roughly 3.2 metres of head, or 0.31 bar, at 1.27 m/s. Through thirty-two millimetre, bore about 26.0 mm, it costs 0.97 metres, or 0.10 bar, at 0.78 m/s. The upsize buys back about a fifth of a bar. On a property with four bar at the boundary that is noise; on a property with one and a half bar and a first floor shower it is the whole margin.
Enter the surveyed route length rather than the plan dimension, the real internal bore rather than the nominal size, and the flow the household actually wants — the answer prices the detour round the tree before anybody digs it.
The total length of the pipe run.
The design flow rate through the pipe.
The pipe material's Hazen-Williams roughness coefficient.
The pipe's actual internal (bore) diameter.
Friction head loss
17.96 ft
They open the calculator with your figures already in it
Domestic Water Pipe Friction Loss Calculator (Hazen-Williams): 17.96 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Hazen-Williams is an empirical fit to cold water in turbulent flow, roughly 40 to 75 °F (4 to 24 °C) at velocities in the 2 to 10 ft/s (0.6 to 3 m/s) band. Outside that it drifts: glycol-charged loops, hot recirculating mains and low-flow trickles are Darcy-Weisbach problems, where viscosity enters the calculation instead of being absorbed into a single C value. The formula still returns a number for any of them; it is just not the loss you will measure.
- Head loss is one term of the pressure the fixture actually sees. What is available is the incoming main, less the static lift to the outlet, less this friction, less the fittings, and less every device in the line — a meter, a backflow preventer, a filter and a softener can take 20 to 30 psi (207 kPa) between them. A run whose friction loss looks comfortable here can still open at a shower with nothing left.
- Velocity is not reported, and velocity is often what sizes the pipe rather than head loss. Copper is normally held near 8 ft/s cold and 5 ft/s or less on hot recirculating lines, because water moving faster erodes the inside of elbows and tees over the years and makes the pipe audible in the wall. A small pipe on a short run can pass a friction check comfortably and still be the wrong size.
Twenty-five or thirty-two, settled while the ground is open
The material question is short. Below ground the pipe is blue polyethylene to BS EN 12201, in PE80 or PE100, normally SDR 11, sold in coils and carrying a Kitemark or equivalent third-party certification. It must be acceptable for contact with water intended for human consumption, which in England means Regulation 31 of the Water Supply (Water Quality) Regulations 2016 and in practice means buying from a merchant who stocks the certified product rather than the cheapest blue coil available. North American work uses the same polymer to a different document, AWWA C901, and the reasoning that follows is unchanged.
The size question is longer, because nominal size is an outside diameter and the water only sees the bore. Twenty-five millimetre MDPE at SDR 11 carries a wall of about 2.3 mm and a bore of about 20.4 mm. Thirty-two millimetre carries about 3.0 mm and a bore of about 26.0 mm. That is a bore twenty-seven per cent larger for an outside diameter twenty-eight per cent larger, down a trench that is exactly the same trench, dug by exactly the same machine, backfilled by exactly the same person. The excavation is the cost of this job and the pipe is a rounding error against it, which is the honest argument for the larger size and the only one that needs making.
Where the fixture count helps is in deciding whether that argument applies to this house. A three-bedroom property with a family bathroom, a shower room and the usual kitchen appliances comes out somewhere around twenty-six water supply fixture units on the Uniform Plumbing Code's private-use table. The number is not portable between documents and this is the place people go wrong with it: the International Plumbing Code's table runs a good deal lower for the same fixtures, and BS EN 806-3 does not count in fixture units at all but in loading units on a curve of its own. Take the count and the sizing method from the same document. Twenty-six units at the conventional 2.4 m/s ceiling wants about 23.4 mm of bore. Twenty-five millimetre MDPE does not have it. Thirty-two does.
Read that result as a direction rather than a prohibition. The 2.4 m/s ceiling is a noise and erosion limit written with pipework inside occupied rooms in mind, and a polyethylene service buried nine hundred millimetres under a lawn is neither in a room nor especially erodible. Plenty of two-bathroom houses run perfectly well on twenty-five millimetre. What the calculation reliably tells you is which way a marginal call falls, and on a long route, a third bathroom, a bath somebody wants filled quickly, or a run under a driveway that nobody will ever open twice, it falls the same way every time.
| Nominal outside diameter | Wall | Internal bore | Where it earns its place |
|---|---|---|---|
| 20 mm | 2.0 mm | 16.0 mm | A single outbuilding tap or a garden supply, and almost nothing else |
| 25 mm | 2.3 mm | 20.4 mm | The default domestic service on a short route with one or two bathrooms |
| 32 mm | 3.0 mm | 26.0 mm | Long routes, three or more bathrooms, or anything crossing hard standing |
| 50 mm | 4.6 mm | 40.8 mm | Shared or multi-dwelling supplies, where the undertaker's terms change too |
Add up the fixture units the property will have after the loft conversion rather than the ones it has today, and read the answer as a bore to compare against the table above — not as an outside diameter to order.
The sum of water supply fixture unit values for every fixture served by this pipe segment.
A calibration constant that scales the square-root approximation to your building's fixture mix.
The maximum velocity allowed in the pipe to limit noise and water hammer risk.
The pressure available where the supply enters the building.
The length of pipe from the point of supply to the furthest fixture, following the run.
How much extra length is added to represent the elbows, tees and valves in the run.
The height of the highest fixture above the point of supply.
The pressure the metering assembly loses at your design flow.
The flow pressure the furthest fixture needs at its inlet to work properly.
Which Hazen-Williams roughness coefficient the friction calculation uses.
Minimum pipe diameter
0.862 in
Velocity governs this run. The diversified demand would fit through a smaller bore on pressure alone, but sustained velocity above the ceiling erodes the pipe and is audible through the building, so the velocity limit is the binding one and the pressure budget has room to spare.
- Estimated peak demand
- 14.31 GPM
- Diameter set by the velocity ceiling
- 0.86 in
- Diameter set by the pressure budget
- 0.77 in
- Pressure lost to static lift
- 58,286.8 Pa
- Pressure lost to friction at this diameter
- 122,120.36 Pa
- Pressure left at the furthest fixture
- 198,803.83 Pa
- Equivalent length used for friction
- 147 ft
They open the calculator with your figures already in it
Domestic Water Pipe Sizing by Fixture Unit Calculator: 0.8616 in — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 0.862 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Fixture-unit methods work because fixtures are used intermittently and rarely together. That diversity is the whole basis of the sizing, and it is why the pipe is far smaller than the sum of the fixture flows would suggest.
- Hunter's curve is old, and its age biases this in one direction. It was derived in the 1940s from fixtures using several times the water modern ones do, and it is well documented as oversizing systems built with low-flow fittings — the demand factor is the handle for that, and lowering it is a judgement with consequences rather than a correction.
- Excludes continuous-demand loads such as irrigation and hose bibs, which do not benefit from diversity and are added at their full flow.
- The friction calculation assumes one diameter for the whole run. A real system steps down as branches leave it, so the true loss is somewhere between this figure and the loss of a system sized entirely at the smallest branch — this is the screening answer, and a segment-by-segment calculation is the design one.
- Fitting losses are an allowance, not a count. Each elbow, tee and valve has its own equivalent length and a push-fit insert reduces the bore as well, so the percentage is a stand-in for a takeoff nobody has done. On a run with many tight bends it will understate the loss.
- The meter figure is yours to supply and this page cannot check it. Meter loss rises steeply as flow approaches the meter's rating and a backflow preventer or pressure-reducing valve often costs more than the meter itself; entering a nominal figure where the real assembly loses far more is the quiet way this calculation goes wrong.
- Velocity limits govern independently of flow: sustained velocities above roughly 2.4 m/s (8 ft/s) cause erosion and noise regardless of what the fixture units allow.
- The result is an internal diameter, not a pipe size. Nominal designations are not bores — copper, PEX and CPVC of the same nominal size have materially different internal diameters, and a push-fit system loses more at every joint — so take the next size up whose actual bore meets this figure in the material you are using.
Four depths, and only one of them is the cover
Depth causes more argument on a service trench than anything else, because four different measurements all get called the depth and three of them are measured to different places. Cover is the one written into the rules: in England and Wales, Schedule 2 of the Water Supply (Water Fittings) Regulations 1999, as set out in the WRAS Water Regulations Guide, gives a supply pipe a minimum of 750 mm and a maximum of 1350 mm from finished ground level to the crown of the pipe. The minimum is frost protection. The maximum is less obvious and is about somebody being able to find and repair the pipe without an excavator, and it is the one people breach by accident when the ground falls away towards the house.
Everything else follows from cover rather than competing with it. The formation the machine digs to is cover plus the pipe plus the bedding beneath it. Under a driveway the governing depth is the crown of the sleeve rather than the crown of the pipe, and the sleeve is there so the drive is never opened again, not because the pipe needs the strength. Outside a maritime climate the frost line overrides the lot: the International Residential Code requires the water service below it, and the figure itself is a local table held by the authority having jurisdiction, not a national number that can be looked up once and reused.
Two separation rules and one ground condition finish the section. A supply pipe does not share a trench with a foul drain, and the two American codes get there by different routes. The International Plumbing Code asks for five feet of undisturbed or compacted earth between the water service and the building sewer, and relaxes that only where the water pipe sits on a solid shelf at one side of a common trench, twelve inches above the top of the sewer. The Uniform Plumbing Code writes no five-foot rule at all: it goes straight to the shared trench and asks for twelve inches of clearance above the drain and twelve inches of horizontal clearance from it, again off a solid shelf. UK practice reaches the same outcome by keeping the two trenches apart. Blue warning tape goes in above the pipe with enough backfill over it that a future spade meets the tape first. And where the ground is contaminated with hydrocarbons or solvents — filling stations, old works, made ground of unknown parentage — ordinary polyethylene is permeable to them and the correct product is a barrier pipe to BS 8588, which is a decision made from the site history rather than from the smell of the spoil.
| Depth | Measured to | What sets it | Who is asking |
|---|---|---|---|
| Cover | the crown of the pipe, from finished ground level | Schedule 2 of the Water Supply (Water Fittings) Regulations 1999 — 750 mm minimum, 1350 mm maximum in England and Wales | the undertaker's inspector on connection day |
| Formation | the trench floor, beneath the bedding | cover, plus the pipe diameter, plus the bedding thickness under it | the machine driver, and whoever is paying for the spoil to leave |
| Frost line | the depth to which local records say the ground freezes | the adopted code and a jurisdictional table — the IRC puts the service below it, but does not publish the figure | anyone building outside a mild maritime climate |
| Duct crown | the top of the sleeve where the route crosses hard standing | the wheel loads above and a firm intention never to break out the drive again | whoever has to resurface afterwards |
Where the pipe stops being buried
The buried run is the easy part. Every burst this installation will ever have is within a metre either side of the point where it comes out of the ground, because that is where cover stops protecting it and nothing has yet replaced the protection. The pipe should arrive through a duct — a length of sleeve cast or cored through the footing or the wall, sized so the service passes through with a gap rather than a squeeze — and that duct is then sealed at both ends. Sealed matters twice: it stops water tracking along the sleeve into the building, and on any site with a radon or ground gas requirement it is a penetration through the barrier and is treated as one.
Inside the duct the pipe rises and stops being a service pipe. Where the riser passes through an unheated void, a garage, or a suspended floor under an uninsulated ground floor, it needs lagging, and the thickness is not a matter of taste: BS 5422 tabulates insulation thicknesses for frost protection against pipe size, material and the exposure period being designed for, and the thickness that stops condensation on a cold main is not the thickness that delays freezing. Insulation on a cold service is best understood as a queue-jumping device. It decides which pipe in the building freezes last, and on a void run that is usually the whole of what is needed, because the cold snap ends before the queue reaches it. Where it is not enough — a long crawl space run, an exposed outbuilding leg — trace heating to the manufacturer's own literature is the answer, and lagging goes over it rather than instead of it.
Finish the entry with the two fittings that make it maintainable. An internal stop tap goes as close to the entry as it can be reached, on a bracket rather than hanging off the pipe, and a drain-off goes immediately downstream of it so the house can be emptied without lifting floorboards. Both want to be somewhere a person can kneel. A stop tap buried behind a fitted cupboard is a stop tap that will be reached with a claw hammer at two in the morning, and the first flood this new service causes will be nothing to do with the pipe.
The entry, from the bedded pipe up to the stop tap
- Internal stop tap and drain-off — the first two fittings anyone will ever reach for, so they belong where a person can kneel rather than behind a fitted cupboard Domestic Water Pipe Sizing by Fixture Unit Calculator
- Lagged riser — the length that is neither buried nor heated, insulated to a frost thickness rather than a condensation one Pipe Insulation Calculator
- Duct seal at the entry — closes the sleeve against tracking water and, on a gas-protected site, restores the barrier the sleeve just breached
- Entry duct through wall or footing — sized so the service passes with a gap rather than a squeeze, which is what lets the pipe be drawn out and replaced later
- Bedded MDPE service — one unjointed length from the boundary, on a bed that supports it continuously instead of letting it bridge stones Domestic Water Pipe Friction Loss Calculator (Hazen-Williams)
This counts sleeves against a measured run, which is exactly the question at the entry: total the riser, the void crossing and the garage leg, and it returns the stock sections to buy. It does not choose a thickness — take that from the BS 5422 tables for the pipe size and exposure.
SettingsSettings for this calculation
The standard allowance most suppliers and estimating guides assume for ordinary work.
The total length of pipe you want to insulate.
Sleeve lost to mitring at elbows and trimming to fit between clips.
Pipe insulation sections needed
9 x 6 ft sections
- Pipe length (with waste)
- 53.9 linear ft
They open the calculator with your figures already in it
Pipe Insulation Calculator: 9 x 6 ft sections — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The count is driven by run length alone, so it does not tell you which sleeve to buy. Tubular insulation is sized both by the pipe's outside diameter and, separately, by wall thickness, and a sleeve one bore size out will either refuse to close around the pipe or sit loose with an air gap running the length of it.
- Nothing here checks whether the insulation is thick enough for the duty. The minimum wall thickness for hot water pipes is set by energy code against pipe size and fluid temperature, and the thickness needed to hold a cold or chilled line above its dew point depends on ambient temperature and relative humidity; both are jurisdictional, and neither is a function of how long the run is.
- The waste allowance covers mitring at bends and trimming to fit, not a fitting-by-fitting take-off. Elbows, tees, valves and flanges are normally covered with pre-formed fitting covers bought separately, and a compact run with many changes of direction can eat well past the 10% default in offcuts.
- The answer counts whole stock sleeves, so the imperial and metric figures are not restatements of one another. A 15 m run comes out as 10 six-foot sleeves, which is 18.3 m of insulation, or as 17 one-metre sleeves, which is 17 m; the piece counts differ because the products differ, and metric merchants also stock 2 m lengths that this count does not assume.
- Only the sleeves are counted. Self-seal tape or ties for the split seam and end caps are extra, and the figure assumes the run can be wrapped end to end: pipe clips, hangers and the points where a pipe passes through a wall interrupt the insulation, and those breaks are where heat loss and freezing concentrate.
The joint that has to outlive everybody
A plastic service pipe reaches the house and then meets metal, and the fitting where that happens is the one nobody will look at again for thirty years. On the buried side the compression coupler wants a pipe insert in the polyethylene and a body specified for below-ground use, which in aggressive water means dezincification-resistant brass rather than ordinary brass; the copper alloy fittings themselves fall under BS EN 1254, and the approval schedules WRAS publishes are the place to check a specific body rather than a merchant's catalogue description. Above ground, the transition is either to copper or to whatever the property already has, and that second case is where the trouble is.
The classic bad pairing on this job is new copper meeting a retained galvanised iron riser. Copper and galvanised steel sit a long way apart in the galvanic series, the joint is permanently wet, and the steel is the metal that pays. It corrodes from the inside outwards, so the failure is invisible until the wall of the iron gives up, and the corrosion products migrate downstream and restrict the very pipework that was just improved. A dielectric union or an approved isolating fitting is the standard answer and most codes require one at any dissimilar-metal joint in a wet system regardless of how the pairing scores.
There is a better answer available on this particular job, which is not to make the joint at all. If the outside run is being renewed because the supply is poor, and there are still six metres of fifteen millimetre galvanised iron between the entry and the kitchen, the iron is very likely a substantial part of the complaint — its bore has been closing for forty years and no calculation done on the new plastic will predict what the old iron does to the result. Renewing to the first appliance while the floor is already up costs a fraction of what it costs as a separate visit.
One consequence has nothing to do with water and gets missed on almost every plastic service installation. A metal incoming main used to be part of the building's earthing arrangement in practice even where it was never meant to be. Replacing it with polyethylene removes that path, and BS 7671 requires main protective bonding to the metallic water installation pipework within the premises, connected at the point the metal begins on the consumer's side. Tell the electrician the service has gone plastic, before the trench closes rather than at the next periodic inspection.
Set the two metals meeting at the entry — new copper against a retained galvanised riser is the pairing to check first. Note that lead is not among its options, which is itself the answer: a lead joint is not a corrosion question, it is a removal one.
The metal on one side of the joint.
The metal on the other side of the joint.
Galvanic corrosion risk level
3 Risk Level (1=Low, 2=Medium, 3=High)
This is general reference guidance based on typical galvanic series relationships for common plumbing metals — always use a dielectric union or approved isolating fitting whenever joining dissimilar metals in a wet system, regardless of the indicated risk level, per code requirements in most jurisdictions.
They open the calculator with your figures already in it
Dielectric Union Galvanic Corrosion Risk Evaluator: 3 Risk Level (1=Low, 2=Medium, 3=High) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 3 Risk Level (1=Low, 2=Medium, 3=High) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- The two metals set the direction of attack; the AREA RATIO sets its speed, and there is no field for it here. All the current leaving a large cathode concentrates onto a small anode, so a steel nipple threaded into a copper system pits through in a season, while the same pair with a large steel body and a small brass insert sits for decades. Copper to steel scores 3 whichever way round it is entered; on site the two cases are years apart.
- Nothing happens at all without an electrolyte, and how aggressive it is changes the whole picture. A dissimilar joint on a dry gas line or in an unheated void never forms a cell; the identical joint in softened, chlorinated or hot recirculating water carries far more current, because conductivity, dissolved oxygen and temperature are the multipliers. A hot return loop is the hardest duty in most buildings and scores the same as the dry one.
- A dielectric fitting interrupts the metal path, not the water path. The water column itself conducts across the gap, so a weak cell can persist through the union, and the fitting's own steel body plus the debris that collects in its restriction is often what fails before the pipe does. Some jurisdictions now favor a length of brass transition over a dielectric union for exactly that reason.
- Galvanic attack is one mechanism, and a score of 1 clears only that one. Dezincification strips yellow brass in aggressive water, erosion-corrosion pits copper wherever velocity runs high or a fitting was left badly reamed, and stray DC from a bonded electrical system or a nearby cathodic-protection installation eats metal with no dissimilar joint involved anywhere.
Test, flush, disinfect, and only then cut over
Polyethylene does not pressure test like copper. It creeps under load, so the pressure falls during the test for reasons that have nothing to do with a leak, and BS EN 805 sets out the regime for water supply systems outside buildings that accounts for that behaviour rather than treating a falling gauge as a failure. Test before backfilling wherever the programme allows, because a joint located while the trench is open is a five-minute repair and the same joint located afterwards is the whole excavation again.
Then get the pipe clean before it feeds anything. A new service arrives with swarf, coil dust and whatever entered the open ends on site, and BS EN 806-4 covers the installation and commissioning of the internal system while PD 855468 gives the flushing and disinfection procedure for services supplying water for domestic use. Some undertakers require disinfection and a satisfactory sample before they will complete the connection, some do not, and it is worth asking rather than assuming, because a chlorination that has to be repeated after the meter is live is a considerably more awkward operation.
- Lay the pipe in one unjointed length from the boundary to the entry wherever the ground allows, and cap both ends the moment the coil is cut.
- Bed and surround the pipe on selected fine material, picking the sharp fraction out of the spoil rather than trusting the compaction plate to sort it.
- Pressure test to the regime in BS EN 805, allowing for the creep behaviour of polyethylene rather than expecting a rigid-pipe gauge trace.
- Photograph the open trench along its whole length with a tape in shot, before any backfill goes in.
- Backfill in layers and compact each one, keeping the plate off the pipe until there is enough cover over it to take the blow.
- Flush the new service at full bore to waste until it runs clear, then disinfect and sample in line with PD 855468 and whatever the undertaker requires.
- Have the connection made, prove flow and pressure at the internal stop tap with the boundary tap fully open, and only then cut the house over.
- Cap the old supply at the boundary end, leave it isolated in the ground, and mark on the record drawing that it is dead.
What gets left behind, and the lead question nobody asks
Reinstatement is judged in eighteen months, not on the day. A trench backfilled in one lift looks perfect on Friday and appears as a settled scar across the lawn by the following spring, and under a drive the same shortcut telegraphs as a crack along the whole route. Where the trench crosses a public footway the standard is not a matter of judgement at all: the Specification for the Reinstatement of Openings in Highways applies, along with the permit conditions from the highway authority, and both are considerably more prescriptive than anything that applies inside the boundary.
Leave a record that survives the owner. A sketch with the route dimensioned off two permanent features — a corner of the house and a gatepost, not a shed — plus the photographs of the open trench, plus the depth, the pipe size and the connection date. Put a copy with the property documents and another in the meter chamber if there is one. Leave the boundary stop tap key with the house rather than in the van. Every one of these takes ten minutes now and saves a day of exploratory digging for whoever owns the property when the pipe next needs attention.
Finally, the lead question, which owners rarely raise and which matters most. If the property had lead and only part of it has gone, the job is not finished and can temporarily be worse: disturbing a lead pipe and leaving a length of it in service is known to raise lead concentrations at the tap for a period afterwards, which is why the Drinking Water Inspectorate's guidance and the US EPA's Lead and Copper Rule both push towards full replacement rather than partial. Where the internal lead cannot go immediately, say so plainly, and tell the household to run the kitchen cold to waste before drawing water for drinking or cooking after any period of standing. That sentence, given honestly at handover, is worth more than the rest of the paperwork.
What to have settled before the machine is delivered
Every line here is either a measurement taken on the route or an answer the undertaker has given in writing. Order the pipe against them, not against the plan dimension between the boundary box and the front wall.
- Surveyed route length, with the drop and the rise added — The trench route with its bends, plus the descent to formation, the rise through the entry, and slack coiled at both ends.
- Fixture units the property will have, not the ones it has — Counted after the loft conversion and the second shower room, because the trench is only cheap while it is already open.
- Cover depth along every part of the route — 750 mm to 1350 mm in England and Wales, measured to the crown, and below the local frost line wherever that governs instead.
- Ducted lengths, and what the duct crosses — Under hard standing, through the footing, and anywhere a future owner might reasonably want the pipe drawn out and replaced.
- Exposed and unheated pipe lengths — The riser, the void crossing and any garage leg, measured separately from the buried run because they are a different purchase.
- The metals meeting at the entry — New pipe against whatever is being retained, so the isolating fitting is on the van rather than fetched on the day.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.