Check void deductions against their own concrete component.
Why can a correct total void still produce an invalid takeoff?
Use the matching calculator
Use this decision sequence
- Assign each void to the component that physically contains it.
- Calculate that component’s gross geometry before deductions.
- Check its deducted volume against its own gross volume.
- Combine only valid net components and keep overlap deductions distinct.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Component gross volume | The local ceiling on a void deduction. |
| Combined project volume | Cannot justify an oversized void in one component. |
| Overlapping voids | Need a union calculation rather than two full deductions. |
Worked comparison
Suppose one component has 0.2 m³ gross volume and another has 1 m³. A 0.3 m³ void assigned to the first component is impossible within that component, even though the combined 1.2 m³ is larger than the void. The correct response is to fix the assignment or measurements, rather than accept the positive grand total of 0.9 m³.
Check before using the estimate
Known voids must be geometrically justified; they are not a substitute for choosing construction specifications.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.
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