Sewer infrastructure.
Where depth changes everything.

What we estimate

We price the full range of sewer infrastructure work, from straightforward subdivision reticulation through to deep main construction in built-up areas:

Pipe sizes from DN150 to DN900. Materials per design specification.

Materials we price

As with water, material choice is made by the designer, in line with the WSA Code and the relevant authority specification. We price what’s specified, with awareness of why each material gets chosen where it does.

For sewer, broadly:

• PVC SN8 — standard sewer reticulation, light-to-medium loading conditions
• PE — flexibility, butt-welded or electrofused joints, common in rising mains and trenchless installations
• DICL — higher loading, larger diameters, where strength and durability demand it
• VC (vitrified clay) — older spec residential reticulation; less common in new design but still encountered in replace-and-upgrade work
• OPVC / MPVC — oriented PVC variants where specified

Each material has its own joint family, its own bedding requirement, its own testing protocol. Sewer mains require select bedding material (typically blue metal), at the right depth below the pipe and above, before backfill.

Where most estimates go wrong — the manhole story

A drawing shows “1 x manhole” as a single circle on the plan. The reality is something we’ve seen across years of pricing this work — that circle hides a stack of components, each of which has its own line in a defensible estimate.

Take a DN1050 manhole (DTC 2203) — the smallest standard size:

• A reinforced base slab with SL81 mesh laid before the walls go up
• Dowel bars placed around the full circumference at the concrete joint between base and wall
• The first 3-metre lift of wall, poured against formwork
• More dowel bars at the joint between that lift and the next
• A second 3-metre lift if depth requires it (and another row of dowel bars at the next joint)
• A tapered top section — because the manhole cover is 600mm, but the chamber is 1050mm. The taper transitions the geometry up to the access opening
• The manhole cover itself — light-duty, Class B, or Class D depending on whether the location takes traffic loads

That’s one symbol on a plan. Seven or eight separate cost lines on the estimate — and we haven’t yet factored in the formwork hire, the labour to build and strip it, the concrete supply, the testing per concrete load, or the shoring required around the manhole excavation itself.

A DN1200 manhole (DTC 2200) is similar in principle but specifies plain concrete walls in one variant and fully reinforced walls in the other (the base is always reinforced). The estimator has to read the design correctly — pricing a fully reinforced manhole when the design only requires plain walls is a substantial cost overrun built into the bid. For the full breakdown of every manhole size we estimate — DN1050, DN1200, DN1500, DN1800, larger and custom-designed structures, including the protective liner rule and 3m lift sequence — see our manholes deep-dive page.

This is the level of attention sewer work needs. Every line item, broken down to its real components, with the right reinforcement, the right joint detail, the right testing allowance. The cost of building this capability in-house is one of the reasons specialist estimating exists.

The same logic applies to concrete encasement. A 12U encasement isn’t just “concrete around the pipe”:

• 100mm of concrete below the pipe
• 150mm of concrete above the pipe
• AG pipes running along the encasement to drain any water that would otherwise build up in the cradle
• Blue metal bags under the pipe so the concrete flows underneath rather than getting blocked
• A next-day backfill — the encasement must cure before any load goes over it

And per current Sydney Water specification, every concrete load requires 3 test cylinders and 1 slump test for compliance, sampled by the concrete supplier. That’s its own line item. Multiplied across every truck on a long encased run, it’s a real cost most generalist estimators miss.

What changes the cost on every sewer project

Sewer estimating has the same condition-stacking as water, but depth amplifies everything.

The depth ladder:

• Beyond 1.5m — trench support required (benching where space allows, shoring boxes where it doesn’t)
• 3m and beyond — for Sydney Water projects, Level 1 Geotech supervision is mandatory. Other authorities have their own requirements; we estimate to the actual authority spec on the project, not to a generic rule
• Up to 6m — workable with a 30-tonne excavator dug directly from surface level
• Beyond 6m — the technique changes. A standard 30-tonne excavator can’t reach below 6m from surface, so the work runs one of two ways: either a long-reach excavator is brought in, or the work area itself is benched down first so the machine starts from a lower surface and digs the remaining depth from there. Either way, a dedicated topside coordinator is required throughout, handing materials and managing communication so the crew below isn’t climbing in and out. Productivity drops noticeably at this point

The machine-size ladder:

• 5-tonne excavators can technically reach about 3m, but they’re inefficient on production runs at that depth
• 23-tonne to 30-tonne classes are the practical workhorses for sewer trenches at typical reticulation depths
• 35-tonne and larger for deep work, manhole excavation, and lifting shoring boxes in and out
• The wrong machine size doesn’t just cost more in plant hire — it costs in lost productivity, and on long runs that compounds quickly

Other variables stacking on top of depth:

• Live road — lane closures or underbore decisions, traffic management plans, road opening permits, reinstatement costs, extended traffic control days when work runs over
• Overhead power lines — a real cost and safety consideration on deep digs. A 30-tonne excavator with a long boom near an overhead line needs extra spotters, restricted working zones, and sometimes a method change
• Underground services — the same shallow-zone problem as water work, but worse because sewer runs deeper, meaning more potential service crossings per metre of excavation
• Live sewer flow — every connection into an existing main requires bypass setup before any cutting starts
• Spoil disposal — deeper trenches generate more spoil, and contaminated material disposal triples the cost per cubic metre
• Ground conditions — rock, clay, sand, groundwater — each one prices differently and most plans don’t tell you which to expect

Sewer bypass — the line item that hides cost

A line on a plan that reads “temporary sewer bypass” can mean anything from a small portable pump on a quiet line through to a multi-week engineered bypass on a high-flow main. The cost variance between those scenarios is enormous, and the difference comes from properly understanding the FIFM (Flow Isolation Flow Management) requirements that govern any work on live sewer.

When we estimate a sewer bypass, we account for:

• Pump redundancy from the start. A live sewer bypass cannot tolerate a single point of failure. If the working pump goes down mid-shift, the flow doesn’t stop — and there’s no “pause the job and call the supplier.” The job runs with a second pump on standby from day one, ready to take over immediately. This is how live bypass actually works; it’s how we price it.
• Pump capacity matched to the flow rate — undersized pumps don’t just risk overflow; they fail authority audit
• Hosing and discharge route — diverting the upstream flow to a downstream manhole or to a tanker, depending on distance and access
• Duration and stand-by costs — the bypass runs until the connection work is complete and tested. A two-day connection can extend to a week if anything is wrong with the existing structure
• Power supply — generator hire if mains power isn’t accessible
• Monitoring — for high-volume flows or longer-duration bypasses, continuous monitoring may be required by the authority
• FIFM compliance documentation — the records and protocols the authority needs to sign off the bypass work

This is the kind of line that’s easy to drop a placeholder number into. We don’t.

What we deliver beyond the obvious

A complete sewer estimate is more than pipe, manholes, and connections. It includes the costs that buyers and head contractors regularly underestimate or miss entirely:

• Trench support — benching allowance OR shoring box hire, freight, setup, multiple box sets for longer runs
• Geotech supervision — Level 1 for depths beyond 3m on Sydney Water work
• Compaction testing — every 150mm layer of backfill, sampled and tested
• Concrete testing — cylinders and slump tests per load, with independent lab reporting
• CCTV inspection — post-installation defect inspection, recorded and reported to authority
• Hydrostatic testing — pressure or air testing of the line per spec, before any handover
• Bypass setup and management — when live connections are involved
• FIFM compliance — documentation, monitoring, authority sign-off
• Sewer odour management — for connections in built-up areas
• Traffic control — when the alignment is in a live road
• Vacuum excavation — when working near live services that can’t tolerate machine excavation
• Tipping fees and contaminated spoil disposal — measured per cubic metre, by category
• Reinstatement — roads, footpaths, driveways, landscaping, private property restoration where the lead-in runs through it

Every estimate includes a thorough assumptions and exclusions register — explicit about what’s been priced in, what’s been qualified out, and what the head contractor still needs to confirm. The price by itself is useful; the price with its assumptions is defensible.

Authority fluency

Sewer specifications are even more rigorously enforced than water, because the consequences of getting them wrong are public-health-grade. Reading the right authority’s spec correctly is core to how we estimate. We estimate to the actual authority spec, not a generic template:

• Sydney Water — full Design and Construction Specifications, including the DTC catalogue (DTC 2200 for DN1200 manholes, DTC 2203 for DN1050 manholes, 12U/12R encasement codes), Section 73 framework
• Hunter Water — Lower Hunter region specifications, with their own manhole and encasement requirements
• Coliban Water and GWM Water — regional Victoria, MRWA-aligned conventions, with regional ground-condition considerations
• Melbourne metro retail water businesses — MRWA-aligned sewer specifications for the metropolitan area
• Regional Queensland councils — council-managed sewer networks with their own procurement frameworks

Each authority has its own current revision of standards, its own preferred materials list, its own acceptance criteria. We work to the right one — not a guess about what might apply.