How Bilby works
How Bilby calculates outdoor stair costs
Treads, width and attached scope
Bilby prices each outdoor staircase from material, resolved tread count and effective width. A stair may attach to a house, deck, pool terrace or path. Landings and guarding can add scope beyond the flight, and entrance steps require checking the house supplier’s inclusions.
Four materials, separate additions
Choose timber, concrete, natural stone or galvanised steel. Native installed flight models use fixed work, tread-width quantity and a minimum. Resolved landings are separate surface area. Above 0.60 m height difference the adapter adds a provisional two-sided timber guarding allowance; that does not certify the required barrier design. Steel and natural-stone landings currently use a concrete-patio surface reference and need specification review.
Native flight specifications
These low / expected / high figures apply before landing or guarding additions. A permitted coordinated setup waiver needs explicit contract context; a normal planner result does not automatically waive it.
| Material | Fixed | Per tread-metre | Minimum |
|---|---|---|---|
| Timber | 5,000 / 8,000 / 12,000 | 800 / 1,400 / 2,200 | 10,000 / 15,000 / 25,000 |
| Concrete | 12,000 / 20,000 / 30,000 | 1,700 / 2,900 / 4,200 | 20,000 / 35,000 / 50,000 |
| Natural stone | 0 / 0 / 0 | 2,916.67 / 4,583.33 / 6,250 (display rounded) | 20,000 / 35,000 / 50,000 |
| Galvanised steel | 15,000 / 25,000 / 40,000 | 2,100 / 3,300 / 5,000 | 25,000 / 40,000 / 65,000 |
Resolved versus assumed stairs
The geometry method uses preliminary exterior proportions: target rise 0.165 m, maximum rise 0.18 m and tread depth 0.28–0.38 m. These are planning rules, not approval of a stair.
| Input | Unit | Where from? |
|---|---|---|
| Tread count and width | count, m | Resolved attachment and terrain |
| Material | choice | Your selection |
| Landing | m² | Resolved length × width |
| Guarding | m | Assumed two sides of flight plus landing |
| Unavailable geometry | tread-m | Fallback five treads × requested width |
Flight formula and precedence
Native timber flight = max(minimum, fixed + tread count × width × rate): fixed SEK 5,000 / 8,000 / 12,000, rate 800 / 1,400 / 2,200 per tread-m, minimum 10,000 / 15,000 / 25,000. Each other material has its own coefficients. Resolved non-house flights can retain native results. A house-attached or unresolved flight receives a disclosed reference instead; its timber reference uses fixed 3,000 / 6,000 / 12,000 plus tread-m × 1,800 / 3,000 / 5,000. The two formulas are alternatives.
Illustrative five-tread timber flight
A fictional resolved flight with five treads and 1.2 m width has 6 tread-metres. Native standalone pricing is max(10,000, 5,000 + 6 × 800) = SEK 10,000 low, 16,400 expected and 25,200 high. The separate five-tread reference is SEK 13,800 / 24,000 / 42,000. These examples exclude landing and guarding. A 1.2 m-long landing at the same width adds 1.44 m² of separately priced surface.
Review attachment and height
Moving a stair or its parent can change rise and tread count even at unchanged width. Missing terrain can trigger assumed geometry. A supplier-included entrance must not be bought twice. The fixed-cost waiver available to explicitly coordinated models is not automatically used by every planner stair. Check the receipt, loading, foundations and actual guarding before procurement.
Method and review
Reviewed 18 October 2026: staircase geometry, installed models active from 4 September and reference catalogue researched 16 September 2026. A manufacturer describes steel stair products, but that does not establish Bilby’s installed labour allowance Weland. Material-specific quotes remain necessary.
The review date covers this explanation and its implemented method. Price and data dates are stated separately in the article.