Perimeter-based conceptual estimating for building works (Which method is appropriate when costs scale with boundary length such as fencing or facade periphery?)

Introduction / Context:
Some building elements scale with perimeter length rather than floor area or volume. Conceptual estimates should therefore use a metric aligned to the primary driver to avoid bias and underestimation.

Given Data / Assumptions:

• Work category: perimeter-driven (e.g., site fencing, boundary walls, facade periphery).
• Scope definition is preliminary; detailed BOQs are unavailable.
• Unit costs per linear metre are available from benchmarks.

Concept / Approach:
Estimating accuracy improves when the cost metric matches the physical driver. For perimeter works, cost per linear metre captures the dominant scaling, enables quick scenario testing (changes in layout), and integrates easily with allowances for gates, corners, and height variations.

Step-by-Step Solution:
1) Identify the principal cost driver (boundary length).2) Apply a benchmark rate per linear metre, adjusted for height, materials, and site conditions.3) Add allowances for fittings (gates, posts), foundations, and contingencies.4) Cross-check against comparable projects' perimeter costs.

Verification / Alternative check:
When the driver is area (floor finishes) or capacity (HVAC tonnage), other methods fit better; perimeter items consistently correlate with length, validating the linear-metre approach.

Why Other Options Are Wrong:
Base unit, function, area, or volume methods misalign the cost driver and can distort early budgets for perimeter-heavy scopes.

Common Pitfalls:
Ignoring corner and gate premiums; not accounting for terrain or access constraints; omitting demolition or tie-ins to existing works.

Final Answer:
Cost per linear metre method