How Bilby works
How Bilby estimates retaining-wall costs
A retaining structure holds ground back
Terrain calculations can estimate structural retaining where the proposed levels need support. That is different from a decorative or boundary wall. A budget label mentioning outdoor retaining walls can currently refer to a non-retaining stone boundary model; check the described scope, not the label alone.
Structural terrain ownership
Native retaining belongs to selected-area terrain and combined house groundworks. It uses estimated wall face area and a severity-dependent construction and design allowance. A garden wall or lawn edge is not automatically the same structure. The lawn retained-edge appearance currently adds no priced retaining structure, so a visible edge does not mean structural support is funded.
Height matters as well as length
Terrain edge level changes drive the estimated retained area. An ordinary grading allowance is distinguished from greater support needs.
| Input | Unit | Where from? |
|---|---|---|
| Edge level differences | m | Terrain versus proposed formation |
| Retained face area | m² | Derived from edge geometry |
| Severity | class | Estimated maximum retaining height |
| Contract ownership | scope | Terrain/house groundwork package |
| Detailed wall design | specification | Not established by planner appearance |
Area rates and design allowance
Native low/expected/high face rates are SEK 2,500 / 3,250 / 4,000 for minor, 4,000 / 5,250 / 6,500 for moderate, 6,000 / 8,000 / 10,000 for significant and 7,000 / 10,000 / 13,000 for major retaining. Design allowances are respectively 0 / 0 / 5,000; 0 / 7,500 / 15,000; 7,500 / 15,000 / 30,000; and 15,000 / 30,000 / 60,000. Scenario face quantities can also vary. A standalone structural reference instead uses fixed 10,000 / 20,000 / 40,000 plus area × 3,500 / 6,000 / 10,000.
Illustrative moderate retaining
For a native moderate case with face quantities 8.5 / 10 / 11.5 m², the retaining components are SEK 34,000 / 60,000 / 89,750. Expected is 10 × 5,250 + 7,500. These component amounts precede whole-terrain rounding and confidence expansion. They are not added again if already in the counted terrain package.
Appearance is not engineering
Moving the house or changing formation level can change support height and cost. Selecting a stone texture does not design a retaining structure. Footings, drainage, surcharge loads, access and stability need a site-specific solution. Without terrain, a wall-face assumption remains provisional. Keep boundary-wall and structural-retaining quotes separate.
Method and review
Reviewed 18 October 2026: terrain rates version 2 and national reference catalogue researched 16 September 2026. Values are Bilby allowances including a design provision, not a contractor guarantee. Geological context can flag conditions requiring specialist assessment SGU.
The review date covers this explanation and its implemented method. Price and data dates are stated separately in the article.