Utility diversion budgets on a constrained site

Utility diversion cost planning goes wrong in a predictable order. The layout is designed, permission is obtained, the contractor mobilises, and then a high voltage cable is found running diagonally across the footprint of block B. By that point the cost is whatever the network operator says it is, the programme is whatever their outage window allows, and neither number was in the appraisal.

None of that is unavoidable. Diversions are expensive and slow, but they are knowable at the point where the land is still being appraised, and the difference between a scheme that budgets for them and one that discovers them is usually a matter of a few thousand pounds of enquiry work.

Find the apparatus before you fix the layout

Order records from every asset owner at the earliest sensible moment, which on a site being acquired means before exchange rather than after. A single-point enquiry service will reach many of the larger networks, but it does not reach all of them, and it will not reach private apparatus serving adjoining occupiers.

Records are indicative, not accurate. Positions are commonly shown to the nearest few metres, depths are rarely shown at all, and abandoned apparatus is frequently omitted or shown as live. So follow the records with a survey.

PAS 128 gives the vocabulary for that survey and it is worth using in the instruction, because it distinguishes a desktop records exercise from site reconnaissance, from geophysical detection, from physical verification by trial hole. Instruct to the level the decision needs. A desktop exercise is enough to establish that a diversion may be required. Only verification by trial hole tells you where the cable actually is, and a diversion budget based on anything less carries a wide margin.

Then put the apparatus on the same drawing as the proposed layout, levels and drainage. That single drawing is what turns a list of constraints into a design decision.

Who owns what, and who you have to ask

Each network has its own owner, process and cost recovery regime, and the request has to go to the right one.

Two legal points shape the commercial position. Under section 185 of the Water Industry Act 1991 the undertaker must move a pipe on the request of the owner or occupier where it is reasonably practicable, and the person requesting bears the cost. The Electricity Act 1989 works in a comparable way for electric lines and plant. So the statutory right to have apparatus moved usually exists. What does not exist is any obligation on the undertaker to do it quickly or at a price you like.

Budget estimates, firm quotations and validity

Most networks offer a two-stage process. A budget estimate, produced from records and a desktop assessment, which is free or inexpensive and carries a wide tolerance. Then a firm quotation, produced after design, which is accurate, costs a fee and has a stated validity period.

Use the budget estimate for the land appraisal and the firm quotation for the construction budget, and never treat the first as the second. Budget estimates commonly move by a large proportion once the network has designed the diversion, because the design determines the route, the jointing, the outage requirement and the reinstatement.

Watch the validity dates. A quotation that expires before the scheme starts on site has to be re-priced, and re-pricing happens at current rates with current material costs. On a scheme where permission takes a year and funding takes another six months, plan to obtain the firm quotation late rather than early, and hold the budget estimate in the appraisal until then.

Ask specifically what each quotation excludes. Reinstatement of surfaces, traffic management, out-of-hours working premiums, and the cost of any highway permit or lane rental under the street works regime are all common exclusions, and on an urban site the traffic management can rival the diversion itself.

Programme risk from long lead diversions

Cost is the number the appraisal notices. Programme is the one that hurts.

High voltage cable diversions, large diameter mains and anything requiring a planned network outage are routinely programmed in months rather than weeks, and the undertaker's own outage windows may limit the work to particular seasons or to periods of low demand. A diversion that has to happen before any groundworks can start therefore sits on the critical path from day one.

1. Identify which diversions are enabling works and which can happen alongside construction.
2. Ask each undertaker for an indicative programme at budget estimate stage, in writing.
3. Establish whether an outage is needed and what notice the undertaker requires for it.
4. Check whether the work is in the highway, since a street works permit and its conditions will add time.
5. Sequence the design so that the diversion design is issued for firm quotation before the main contract is let.
6. Build the diversion into the construction programme as a named activity with a float allowance, not as a note.

A Construction Management Plan submitted with the application is a useful place to record the enabling works sequence, because it forces the question early and it gives the authority something concrete to condition.

Build over and build near as alternatives

Where the apparatus is a public sewer, diversion is not the only option. A build over or build near agreement with the sewerage undertaker allows construction over or close to the pipe, subject to conditions about foundation design, access provision, pipe condition and future maintenance.

It is normally faster and less expensive than a diversion, and it is refused more often than developers expect. The undertaker will look at pipe material and condition, depth, diameter, whether it is a rising main, whether manholes remain accessible, and whether the proposed foundations transfer load onto the pipe. A CCTV survey of the pipe is usually required and sometimes reveals that the pipe needs relining first, at the developer's cost.

Design the foundations for the agreement rather than seeking the agreement for the foundations. A piled or bridged solution over the pipe, with a clear zone either side, is far more likely to be accepted than a strip footing that happens to miss it.

Watch the transferred drains. Many private sewers became public in 2011, and a drain shown on an old survey as private may now be the undertaker's, which changes who you have to ask and what you have to agree.

Easements, wayleaves and what they cost you in land

Apparatus that stays carries rights with it. An easement or a wayleave over part of the site restricts what can be built there, and the restriction is usually expressed as a corridor either side of the apparatus within which no building, no tree planting and sometimes no change of level is permitted.

That corridor is developable area you do not have. Establish it at appraisal, draw it on the constraints plan, and test whether the scheme still works with it excluded. A 6 metre easement across a small site can remove a plot, and discovering that after the land has been valued on a unit count is an expensive way to learn it.

Where a diversion creates a new route, a new easement will be required over the new line, sometimes from a third party. Negotiating that consent is a separate workstream with its own timescale, and a neighbouring owner under no obligation to agree.

Holding a contingency that survives the appraisal

A Utilities Assessment setting out existing apparatus, required diversions, proposed connections and the enabling works sequence is the document that keeps all of this in one place. Where the scheme goes to a Viability Assessment, diversion costs sit in the abnormals, and they have to be evidenced by the undertakers' own estimates rather than by an allowance, because a reviewer will ask for the correspondence.

Illustrative example. A 0.4 hectare brownfield site with an 11 kV cable crossing one corner and a transferred foul sewer running beneath the proposed access. The budget estimates cover the cable diversion and a build over agreement for the sewer. The cable diversion is enabling work requiring a planned outage, so it is programmed ahead of groundworks with float. The sewer CCTV survey finds a cracked length that needs relining before the agreement is granted, which is priced as a separate item. Both figures sit in the abnormals with the correspondence appended. These figures and stages are illustrative rather than drawn from a real scheme.

Hold a contingency on the diversion line specifically, rather than relying on the general contingency, and set it by reference to the quality of the information. A budget estimate from records deserves a wide allowance. A firm quotation against a verified survey deserves a narrow one. Our notes on the real cost of an invalid planning application and on levy instalment policies cover the other cash-flow items that tend to be underestimated at the same stage.

This is general guidance, not legal advice; check the position with each statutory undertaker and a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

See PlanScope pricing if you want fixed-cost drafts of the utilities and construction management documents for a constrained site.