Understanding your Build suitability score

Read the score together with its source

Build suitability summarises the available analysis on a 0–100 scale. Higher generally means fewer identified constraints. It is not a probability of receiving permission, a contractor quotation or a substitute for site investigation. Bilby currently has several aggregate paths, so a score in a listing, a plot detail page and a saved project need not be identical.

Listed plot detail: weighted available components

The plot-detail overview calculates (3 × soil + 3 × terrain + 2 × planning + 1 × utilities) ÷ the sum of weights actually available, then rounds to a whole point. Each included component is limited to 0–100. An unavailable component is omitted along with its weight, rather than being treated as zero. Planning’s neutral 50 can still be present even when planning evidence is absent; read its coverage separately.

Fictional example: soil 90, terrain 60, planning 50 and combined utilities 80 give (270 + 180 + 100 + 80) ÷ 9 = 70. With utilities unavailable, the result is 550 ÷ 8 = 68.75, displayed as 69. The detail overview labels 75–100 “Favourable”, 45–74 “Needs attention” and 0–44 “High concern”; no available score is “Assessment pending”.

Coordinate analysis and coordinate projects: equal mean

Coordinate analysis currently averages available soil, terrain and electricity-only utility scores equally, rounding to a whole point. Its planning lookup does not supply the full listed-plot planning score, and water/wastewater are not silently inserted into the utility component. A project based on a coordinate-analysis snapshot uses the same equal-weight approach.

Fictional example: soil 90, terrain 60 and electricity 80 give (90 + 60 + 80) ÷ 3 = 77 after rounding. If electricity is unavailable, (90 + 60) ÷ 2 = 75. If all three are missing, there is no aggregate. “Complete” electricity evidence only refers to electricity, not all services.

Saved listed assessments and older listing values

A listed-plot project summary can display the stored assessment’s aggregate and version. It deliberately does not recompute that value from the visible component rows. Fictional example: a saved assessment with aggregate 72 and components 90, 60, 50 and 80 continues to show 72 in that project summary; the live detail calculation above would show 70. The assessment date and origin explain the distinction.

Listing/map helpers first use an available stored numeric Build or legacy risk/buildability value, rounded and limited to 0–100. Fictional example: a stored 81.6 displays as 82. If no numeric value exists, legacy risk text can map low risk to 87, medium risk to 68 and high risk to 42. Those are label-based fallbacks, not reconstructed weighted analyses. Unrecognised or missing text leaves no score.

What to compare

Compare like-for-like scopes and dates before comparing points.

Score and confidence answer different questions

The score describes assessed conditions; confidence and coverage describe the evidence behind them. A high result based on one available component is not a comprehensive site approval. Changing the chosen house or a budget override does not directly alter these overview formulas. Updated source data can change components. Foundation rankings, selected-pad terrain calculations and the internal groundworks cost-burden classification are different methods; they are not extra components to add to Build suitability.

Method and review

The displayed aggregate paths and their callers were reviewed on 18 October 2026. The weights and legacy fallback values are Bilby product methods. SGU, terrain providers, municipalities and utilities provide inputs; they do not publish or endorse this combined score. Open the individual score articles below to inspect their evidence, thresholds and limitations.