How Bilby works
Understand your budget, the evidence behind each score, and how to use the site planner and house builder.
Getting started
Budgets and assumptions
Groundworks and foundations
How Bilby calculates groundwork costs
Excavation, replacement, fill, transport and shared work beneath and around the house.
How Bilby calculates foundation costs
Structural foundation prices for a slab, crawlspace, piers or basement, and what remains separate.
How slopes and house placement affect groundwork costs
The selected house pad, cut and fill, reused material and the difference from a plot-wide terrain score.
Rock excavation and blasting costs
Estimated rock volumes, blasting setup, inspection and monitoring without counting the same rock twice.
Piling and ground improvement costs
Weak-soil allowances, alternative treatment strategies and the reference calculation for pile metres.
Geotechnical investigation costs
When an investigation allowance is included in groundworks and how to replace it with a scoped offer.
Site clearance and preparation costs
Vegetation, trees, demolition, temporary access and services, and conditional remediation allowances.
Drainage and water-management costs
Dewatering, foundation drainage and local stormwater measures, with separate municipal charges.
How Bilby estimates retaining-wall costs
Structural retaining needs, wall face area and design allowances versus decorative boundary walls.
Garden and outdoor costs
How Bilby calculates driveway costs
Six driveway surfaces, measured area, minimum charges and extras outside ordinary construction.
Lawn and levelling costs
Four lawn choices, topsoil, seed or turf, terrain grading and shared mobilisation.
Deck, railing and gate costs
Net timber surfaces, raised supports, skirting, railings, gates and real coating work.
Patio and garden-path costs
Six patio materials, three path materials, net geometry, base preparation and raised fill.
How Bilby calculates outdoor stair costs
Four stair materials, resolved tread count and width, landings, guarding and provisional geometry.
Fences, boundary walls and gates
Net fence length, gates, timber finishes and the difference between a boundary wall and a retaining structure.
Trees, shrubs and hedges
How supplied plant size, hedge length and width affect planting allowances.
Garden beds, growing boxes and planting
Prepared soil, timber frames, flowers and mixed planting, with edging and irrigation explained separately.
Pools and hot tubs
Pool area, extra depth and installed spa allowances, including what the surrounding deck adds.
Secondary buildings and equipment
Garage costs
Cold and insulated garages, shell, slab and groundworks without counting included components twice.
Carport costs
Roof, posts, footings and optional screens, with the parking surface budgeted separately.
Greenhouses and other outbuildings
Greenhouse size tiers, prepared ground and separate allowances for storage buildings and fit-out.
Outdoor furniture, equipment and lighting
Furniture sizes and installed product allowances for dining, lounging, play equipment and light points.
Connections and services
Municipal water and wastewater
Municipal tariff calculations, reference allowances, service choices and included on-plot work.
Private well costs
Regional well allowances, national fallback prices and what nearby boreholes can and cannot tell you.
Private wastewater system costs
Installation ranges, municipality application fees and evidence that calls for a specialist assessment.
Electricity connection costs
The nearby-building analysis and the separate distance-based budget reference, with 2026 fee bands.
Fibre connection costs
Project-specific connection prices, fallback allowances and separate conduit and subscriptions.
Trenches, pipes and cables on the plot
One shared trench, individual service materials, terminations and the editable assumed route length.
House costs
House package prices and options
Actual house prices, turnkey scope, supplier inclusions and percentage or area-based option reserves.
House delivery, crane and assembly
Delivery loads, billable crane hours and erection area for work outside the house package.
House completion and installations
Finishes, kitchen, bathrooms, heating and other installations, reconciled with the supplier package.
Purchase, approvals and finance
Land registration and mortgage deeds
Lagfart and pantbrev formulas, existing deeds, rounding and provisional reserves when values are missing.
Plot purchase and subdivision
Actual plot prices, optional property formation and purchase-administration allowances.
Permits, maps, setting-out and location checks
Understand local municipal fees, separate survey services and Bilby’s national fallback allowances.
Design, drawings and energy calculations
See how drawing adaptation, technical design hours and energy calculations enter the budget.
Control manager, inspections and testing
Separate the control manager’s assignment from inspections, airtightness and ventilation tests.
Completion protection and construction insurance
Understand premium reserves, covered contract values and insurance already included by a supplier.
Construction-loan interest and fees
Calculate temporary credit costs from the credit limit, average use, duration, interest and fees.
Deposit, borrowing and monthly mortgage costs
Understand own contribution, lender valuation, funding gaps, amortisation and the higher-interest scenario.
Contingency and additional allowances
See which construction costs form the contingency base and how reserves differ from estimate ranges.
Waste, cleaning, temporary housing and moving
Understand waste loads, cleaning hours, extra accommodation months and moving allowances.
Scores and recommendations
Understanding your Build suitability score
Why plot detail, coordinate analysis, projects and older listings can display different aggregate scores.
How the soil and ground score works
Follow the soil family, depth bands, evidence modifiers and conservative limits behind the ground score.
Soil depth and nearby boreholes
How SGU’s model and nearby well observations are blended, with a range and separate confidence.
Terrain score and suggested build area
Understand terrain cells, candidate areas, slope thresholds, boundary assumptions and selected house pads.
How the planning score works
Read the six weighted planning criteria, neutral unknowns, evidence coverage and confidence correctly.
How utilities are scored
Compare combined water, wastewater and electricity scoring with the electricity-only coordinate assessment.
How Bilby recommends a foundation
Understand the displayed foundation categories, site evidence, internal ranking and specialist-review triggers.
Related data
Nearby places, distances and travel times
How nearby amenities are found and why straight-line distance differs from walking, cycling and driving time.
Local weather and seasonal temperatures
Distinguish current forecast context from Bilby’s seasonal averages of nearby SMHI station observations.
Understanding local reported-crime statistics
Read municipality offence rates, police-region comparisons and category shares without treating them as a safety score.