How Bilby works
Lawn and levelling costs
Choose how much of the ground to change
Existing-slope grass follows the current ground; gently levelled grass and maximum-flat grass add grading; prepared-for-grass stops before grass establishment. Bilby uses net lawn area after higher-priority surfaces and overlapping objects, so drawing grass through a house or deck does not intentionally buy lawn twice.
Seed and turf are different specifications
The terrain-aware finished-lawn method assumes seed, delivered topsoil and installation. It adds incremental grading, rock and transport where needed. Its mobilisation is charged once, sometimes owned by house groundworks. The reference fallback uses topsoil, fine grading and a turf finish; prepared-for-grass omits that finish. Structural retaining is excluded from the native lawn scope. Retained-edge appearance does not currently price a supporting wall.
Net plan area and sloping surface
The terrain-aware method uses surface area, which can exceed horizontal plan area. Difficult soil changes topsoil depth. The reference path uses a disclosed depth and, without terrain, an assumed grading volume.
| Input | Unit | Where from? |
|---|---|---|
| Lawn type and net area | m² | Drawn polygon minus shared-surface exclusions |
| Surface area and slope | m², % | Terrain sampling or slope fallback |
| Topsoil depth | m | Native standard 0.10 / 0.15 / 0.20; difficult 0.15 / 0.20 / 0.25 |
| Grading, imports and exports | m³ | Terrain balance or explicit assumption |
| Mobilisation owner | scope | Lawn or house groundworks |
Establishment plus additional grading
Native establishment = surface area × topsoil depth × 1.2 settlement factor × 1.3 t/m³ × delivered rate + surface area × installation rate × slope factor. Delivered rates are SEK 290 / 425 / 560 per tonne; installation 45 / 60 / 85 per m². Slope factor starts at 1 below 5% and rises by bands. Grading and shared mobilisation are separate. Without terrain, reference gently levelled and maximum-flat grading can assume 0.10 or 0.30 m³ handled per m²; this is not proof of feasibility.
Illustrative level 100 m² lawn
For standard soil, 100 m² surface and slope factor 1, native seeded establishment is SEK 9,024 / 15,945 / 25,972. Expected topsoil is 100 × 0.15 × 1.2 × 1.3 = 23.4 tonnes; 23.4 × 425 + 100 × 60 = 15,945. This excludes mobilisation and grading. The reference existing-slope turf package at 100 m² with 15 m³ topsoil instead totals SEK 19,250 / 34,000 / 58,500, including its setup and fine grading. Do not compare these as identical products.
What changes and what stays separate
Resizing, slopes, soil preparation and grading alter cost. Extra topsoil or levelling outside the base scope can be separate; avoid adding its existing base quantities again. Cosmetic edge choices do not prove retention is funded. Missing terrain routes work to a provisional reference. Confidence expansion can widen the native final range beyond component totals.
Method and review
Reviewed 18 October 2026: lawn cost/rates version 1 and reference catalogue researched 16 September 2026. Native seed and fallback turf are retained as distinct implemented assumptions. Contractor material and labour evidence is not a surveyed earthwork quantity Sanmab.
The review date covers this explanation and its implemented method. Price and data dates are stated separately in the article.