3. What a Global Variable Is

A Global Variable is a project parameter that other calculations in the model depend on. Rather than entering hundreds of quantities and rates directly, the user defines a comparatively small set of variables that describe the project at a level a client or design lead would naturally think in. Representative examples include:

• Site area and building footprint
• Structural grid dimensions and number of floors
• Floor-to-floor heights
• Target construction budget
• Structural system and foundation type
• Building use classification (e.g. office, residential, hotel)
• Financial assumptions (contingency percentage, escalation, financing basis)

Each variable is referenced by one or more formulas elsewhere in the model. Changing a single variable — for instance, increasing floor-to-floor height, or switching the structural system from a concrete frame to structural steel — propagates through every formula that depends on it, and the model recalculates the affected quantities, durations, fees, and costs. This is the mechanism that allows a feasibility study to be revised in minutes rather than rebuilt over days.

This extends the Global Variables feature already available within Methvin’s Estimating module — where a variable is set once and applied everywhere it is referenced — into a full feasibility methodology: a defined library of formulas that connects those variables to geometry, structure, programme, and a resource-based cost plan, rather than to a single estimate line.

The variables above are illustrative; the specific set used varies by project type and sector.

4. From Inputs to a Connected Project Model

Once the Global Variables are set, the model derives a series of outputs across six broad categories. These are not independent calculations — a change in one category typically affects several others, since geometry drives structural quantities, structural quantities drive programme duration, and programme duration affects preliminaries and financing cost.

4.1 Building geometry

• Gross floor area and gross building area
• Building footprint and perimeter
• Overall building height
• Basement area, where applicable

4.2 Structural quantities

• Column and beam quantities, derived from the structural grid and floor count
• Structural frame volumes
• Foundation pile quantities and total pile length
• Retaining wall requirements, where site conditions require them

4.3 Building services

• Lift and stair quantities, sized to building height and occupancy
• Water main sizing
• Allowances for core service infrastructure

4.4 Interior planning

• Space allocation by function — office, residential, hotel accommodation — according to the building use classification
• Occupancy calculations

4.5 Programme and delivery

• Design duration and construction duration
• Indicative start and completion dates
• Total project delivery period

4.6 Professional services and client-side provisions

• Architectural, structural, civil, and geotechnical fee estimates
• MEP design, environmental, and sustainability consulting allowances
• Contingency, insurance, and legal provisions
• Furniture, equipment, and operational allowances
• Financing cost, where a financing basis has been defined

Because these categories are cross-linked, the model behaves as a single feasibility engine rather than a set of separate spreadsheets stitched together after the fact. A revision to the structural system, for example, changes column and beam quantities, which changes the resource-based cost build-up, which changes the total budget — and the change is visible immediately rather than after a manual re-estimate.

5. The Dependency Chain: How a Variable Becomes a Cost

The mechanism underlying all of this is a dependency chain that runs from a Global Variable, through a formula, to a quantity, a resource, a cost, and ultimately a position in the programme. In outline, for a structural element, that chain runs as shown below.

Two things follow from this structure. First, cost and programme are not produced by separate exercises that are reconciled afterwards — they are derived from the same resource quantities, so a change to a structural quantity moves both together. Second, the chain can be read in either direction: forward, from variable to total cost, to build the estimate; or backward, from a total cost, through the resource and quantity that produced it, to the formula and Global Variable it depends on, to review the estimate. That reverse path is what makes the model auditable rather than simply automated.