Drawbridge Designs · Civil Estimating · Residential Subdivisions
Practical insights, hard-won lessons, and honest opinions on estimating earthworks, pavements, and stormwater — from someone who's spent years in the trench.
Thoughts & Notes
Monday 9am sales calls — don't do it
Everyone is trying to start their week. Their inbox is full, their calendar just loaded, and you're the third person to call before they've had coffee. There's a reason it never converts — and it's not your pitch.
Underpaying consultants — you're just overpaying in the long run
Squeezing a consultant's fee feels like a win on paper. But the real cost shows up later: in corners cut, in gaps missed, in the good ones quietly walking out the door. The maths doesn't work the way clients think it does.
Deleting quantities from the BOQ before issuing for tender — why?
It's a common practice and a genuinely puzzling one. Stripping quantities out of a bill of quantities before tender doesn't protect anyone — it just shifts risk in ways that usually come back to bite the client. Here's the case against it.
Picking contractors based on preliminary SOR pricing
Using a schedule of rates at early tender stage to shortlist contractors sounds efficient. In practice, it selects for whoever priced the SOR most aggressively — not who will actually deliver. A few thoughts on what to look at instead.
The most common scope gaps in residential subdivisions
After reviewing enough civil estimates, the same items keep falling through the cracks — temporary works, line marking, adjustments to existing infrastructure, and a handful of others that seem obvious in hindsight. Here's the list worth checking before you tender.
Client wants to manage utilities — watch what your subcontractors exclude
When a client takes on utility coordination directly, it sounds like one less headache. But subcontractors notice — and they price accordingly. Knowing what gets quietly dropped from scope is half the battle at tender adjudication.
Estimating Services
Need a number you can actually defend? I provide independent civil cost estimates for residential subdivision projects — from early feasibility through to tender review.
Cut/fill volumes, bulk excavation, import/export, compaction, benching, batters, and retaining structures.
Subbase, base course, asphalt, kerb and channel, footpaths, and driveways to council standards.
Pit and pipe networks, detention basins, OSD systems, headwalls, and drainage infrastructure.
Early-stage order-of-magnitude estimates, concept budgets, and independent tender price reviews.
How Long Does a Detailed Estimate Take?
A detailed civil estimate for a 30-lot residential subdivision is a 10-day process when done properly. Here's how that time is actually spent.
Document Review & Scope Assessment
Reading through all DA and scope documents, reviewing geotechnical reports, pavement designs, and Remediation Action Plans. Identifying gaps and requesting additional information — including TIN files for earthworks quantities.
2D Quantity Take-Offs
Measuring pavement areas, kerb and channel lengths, footpaths, driveways, and all linear infrastructure from design drawings. The foundation that everything else builds on.
3D Earthworks Quantities — Including Rock
Running the 3D earthworks model using TIN files, calculating cut and fill volumes, and assessing rock allowances from geotech data. Swell, shrinkage, and import/export quantities calculated here.
Stormwater & Retaining Wall Quantities
Pit and pipe schedules, detention basin volumes, headwall quantities, and retaining wall take-offs. These items carry significant cost risk and deserve dedicated time rather than being squeezed into a general take-off day.
Requesting Subcontractor Quotes
Issuing scopes and drawings to subcontractors for specialist items — concrete, pipelaying, retaining structures, landscaping, and services. Scope documents prepared from the quantity take-offs completed in prior days.
Compiling & Reviewing Quotes
Receiving and reviewing subcontractor quotes — checking scope coverage, exclusions, and assumptions. Chasing missing quotes and making adjustments where quotes are incomplete or clearly out of range.
Pricing
Building the full cost plan in Benchmark — applying rates, entering quantities, pricing preliminaries, and reviewing the estimate line by line. Sense-checking totals against per-lot and per-m² benchmarks before the report is drafted.
Programme & Finalisation
Producing the construction programme, finalising the cost report, writing the assumptions and exclusions schedule, and issuing for review. The programme informs the preliminaries — both should be completed together.
Total Estimate Duration
30-lot residential subdivision · detailed tender estimate
Resources
Steel Reinforcement (Reo) Calculator
Calculate steel reinforcement quantities by bar size, spacing, and layout for slabs and walls. Includes cost estimation by bar type. Rates sourced from ARC.
Gradework Procedures Guide
Step-by-step procedures for setting up and running earthworks models in Agtek Gradework — from project creation and surface import through to volume calculation and anomaly finding.
Gradework Hot Keys — Searchable Reference
All Agtek Gradework keyboard shortcuts in a searchable, filterable format. Covers mode switching, view controls, data editing, and print preview.
Getting Started with Benchmark Estimating
A practical walkthrough covering project setup, rate libraries, BOQ structure, quantity entry, pricing, preliminaries, and producing a cost report — tailored for residential subdivision work.
Sample MS Project — Residential Subdivision Programme
A ready-to-use Microsoft Project template for a typical residential subdivision, covering civil works from bulk earthworks through to practical completion and defects. Coming soon.
Get in Touch
Whether you need an estimate, a second opinion, or just want to ask a question — drop me a message and I'll get back to you within a couple of days.