Expenses in Modules

In Darwin, expenses represent costs that are real, recurring, and necessary —
but are not materials or labor.

They capture the “everything else” that makes construction possible: permits, stipends, logistics, mobilization, inspections, and similar items.

Modeling expenses correctly is essential for realistic estimates.

What Are Expenses?

Expenses are non-material, non-labor costs that are associated with a module or scope of work.

Common examples include:

Permits and fees
Mobilization and demobilization
Stipends and allowances
Temporary facilities
Transportation and logistics
Site access or inspection fees
Environmental or regulatory charges

These costs often depend on context, not quantities alone.

Why Expenses Belong Inside Modules

Expenses are rarely isolated line items.

They usually belong to a specific scope of work: a foundation module, a structural package, an MEP assembly, etc.

By placing expenses inside modules:

Costs stay tied to their technical scope
Reuse becomes consistent across projects
Estimations remain complete and realistic
Future estimates can reuse reviewed expense logic

Modules become full representations of how work is actually delivered.

Types of Expenses in Darwin

Darwin supports multiple ways to model expenses, depending on how the cost behaves.

1. Amount Expenses

Amount expenses use a coefficient × unit price. Inside a module, their charge basis decides whether they apply once per module occurrence or scale with the module quantity.

Examples:

Permit fee
Inspection fee
One-time mobilization cost

Example:

Building permit → $2,500
Site inspection → $800

Use PerModule for a one-time amount and PerUnit when the amount scales with module quantity. Entering “$2 per m²” as PerModule charges $2 in total, not $2 for every m².

2. Percentage-Based Expenses

These expenses scale relative to the cost of materials, labor, or the entire module.

Examples:

General overhead
Insurance
Contingency
Administrative fees

Example:

Overhead → 5% of materials + labor + amount expenses
Insurance → 2% of labor cost

This is useful when the expense grows as the scope grows.

Each expense type has one of seven calculation codes:

Code	Calculation
`A`	Amount: coefficient × unit price
`D`	Direct amount: coefficient × unit price
`S`	Subcontract amount: coefficient × unit price
`T`	Percentage of materials + labor + amount expenses in its scope
`M`	Percentage of materials in its scope
`L`	Percentage of labor in its scope
`E`	Percentage of amount expenses in its scope

Percentages do not compound on other percentages. A module expense uses its module’s scope; standalone direct percentage expenses use standalone direct lines, while indirect percentage expenses use estimate direct totals (T also includes indirect materials, labor, and amount expenses). All seven codes use the Expense margin, including M: a percentage of materials is still an expense.

3. Distance-Affected Expenses

Some expenses depend on project location or distance.

Examples:

Transportation of crews
Per diem or stipends
Equipment hauling
Remote site logistics

When an amount expense is linked to a Transportation Rate, its unit price includes rate per km × distance. Review that rate and project distance before relying on the amount.

This allows the same module to behave differently depending on where the project is executed.

Choose the Module Expense Charge Basis

Choose the charge basis on each recipe line in the module editor:

Basis	What the estimate charges	Example at 100 m²
PerModule	coefficient × unit price, once per module occurrence	$200 mobilization remains $200
PerUnit	coefficient × unit price × module quantity	$2 haulage per m² becomes $200

Manually added lines default to PerModule. Material-linked and AI-generated lines default to PerUnit, because their coefficients are per module unit. Review those defaults before saving.

Existing expense lines kept PerModule when charge basis was introduced; their totals were not changed automatically. Review older recipes that were intended as per-unit costs. Changing a catalog recipe does not change an existing estimate on an ordinary save; explicit recalculation picks up the reviewed changes.

Inside a composite/bundle, each bundle unit contains an occurrence of its child modules, so both kinds of child expense scale with bundle quantity. When merging modules, PerModule amounts are added once and PerUnit coefficients scale with the selected source quantities; source modules stay unchanged.

Read Fixed and Variable Costs

Fixed/Variable describes whether a cost scales with the owner’s quantity. It is separate from Direct/Indirect, which describes cost nature.

Materials, labor, and PerUnit amount expenses are variable.
PerModule amount expenses are fixed relative to module quantity.
M/L percentage expenses are variable; E/T split according to the fixed and variable parts of their base.
Fixed subtotal + variable subtotal equals the total.
Effective rate is total ÷ quantity, including fixed amounts spread over that quantity. It can fall when quantity increases even though the variable unit cost stays the same. At zero quantity, unit rates are shown as —, not zero.

Use the fixed/variable breakdown when reviewing a quantity change. Composite rows scale with bundle quantity and therefore have no fixed component at that level.

Standalone Expense Pricing

Standard / Lump Sum pricing mode applies to standalone expense lines, not module recipes. A standalone Lump Sum is charged once and has quantity 1. Module expenses use Standard pricing plus the charge basis described above. Percentage expenses use the ls unit; that unit does not itself decide cost behavior.

Typical Expense Examples in Real Projects

Here are common patterns estimators model using expenses:

Crew stipend → fixed daily amount, affected by distance
Mobilization → fixed amount per project
Permits → fixed per module or per project
Logistics surcharge → percentage-based
Remote site allowance → distance-adjusted

These costs are often forgotten in early estimates — Darwin ensures they’re consistently included.

How Expenses Behave Across Projects

Once defined inside a module:

Expenses are reused automatically
Percentage logic remains consistent
Distance rules apply per project
Catalog changes become available to new estimates and explicit recalculation, not automatic updates to existing estimates

This is where Darwin reduces risk:
expenses stop being “remembered manually” and start being systematically applied.

Best Practices

Keep repeatable scope expenses inside modules; use standalone lines for project-specific costs
Use fixed amounts for permits and one-time fees
Check PerModule / PerUnit on every amount expense, especially older recipes and AI drafts
Use percentages for overhead-type costs
Use distance logic for logistics and stipends
Review expenses carefully in your first project
Benefit from reuse and consistency in future projects

Expenses and Reusability

Expenses are part of why the second project is faster.

Once you’ve modeled:

permits
stipends
logistics
overhead

You don’t rebuild them — you reuse them.

Review the reused expenses against the project’s scope so you can identify anything missing or charged on the wrong basis.

Summary

Expenses allow modules to represent real-world construction costs, not just quantities.

They account for:

Context
Location
Scale
Operational reality

By modeling expenses correctly, Darwin becomes a true cost intelligence system — not just a quantity calculator.

Next Steps

Review expenses in your first project modules
Adjust them until they reflect reality
Reuse them in your next project
Observe how consistency and speed improve

Expenses are not an afterthought — they are part of the system.