By JLG Estimating · Published October 15, 2026
1. Lock the original estimating baseline
Record the drawings, specification issue, schedules and addenda included in the original takeoff. Save the workbook version that corresponds to that set. A file labelled final can still be ambiguous if nobody knows which drawing issue it measures.
When a new bulletin arrives, record its number, issue date, received date and requested bid deadline. Identify the sheets and specification sections it replaces. Read narrative instructions as well as drawings; a scope change may be described without a new symbol on the plan.
2. Compare more than the highlighted revision cloud
Use a drawing comparison or overlay as an aid to finding changes, not as the sole decision-maker. Reconcile revised plans with risers, one-lines, schedules and written specifications. A changed equipment tag can affect another trade even if that trade's plan was not reissued.
Classify each difference: a new item, a deletion, a relocation, a material change, a changed capacity or an unchanged item shown on a replacement sheet. Relocation may change route length and labor conditions even when the equipment count stays the same.
3. Track both added and deleted quantities
Use separate original, added, deleted and revised quantity columns. Keep units consistent and explain which drawing controls the change. A net difference alone can conceal a substantial reroute where old work is removed and new work is added.
In the example below, 30 LF was added and 10 LF deleted. Reporting only the 20 LF net increase loses the scope history. If demolition, installation or procurement costs differ, those distinctions may also affect the priced revision.
4. Check the trade interfaces
A revised mechanical unit can change electrical connection requirements, piping trim, controls, support details or access needs. Record the affected interfaces and confirm responsibility from the current documents. Do not assume that another trade's unchanged sheet means no change to its package.
Identify missing information in a clarification log. Include the drawing reference, the question and the estimating assumption awaiting confirmation. Keep owner decisions, design questions and contractor pricing choices distinguishable.
5. Revisit quotes and labor inputs
Quantity changes do not capture every cost change. A different equipment specification can invalidate a previous quotation. A revised installation phase can affect access or working conditions. Check quote revision dates, scope, freight, validity and the supplier's response to the changed specification.
Do not automatically carry the original labor rate or productivity assumption into a materially different scope. Preserve the original basis, describe the changed condition and ask the contractor which input should govern the revised bid.
6. Agree the revised deliverables and deadline
Confirm whether the request is a delta-only review, replacement takeoff sheets or a complete repriced workbook. State which unchanged scopes were carried forward. Agree any additional fee and delivery milestone before treating an expanded drawing set as included work.
At handoff, identify the new baseline and list open clarifications. Ask the receiving estimator to acknowledge the drawing issue used for the final tender. An organized revision record helps the team compare like-for-like numbers; it does not guarantee the design is complete or the bid will be awarded.
- Original and revised document registers
- Added, deleted and revised quantities
- Cross-trade impacts and unresolved clarifications
- Updated quotations and pricing assumptions
- Revised workbook/version and agreed delivery
Quantity-delta example
Illustrative pipe quantities, not a completed client revision.
| Original | Added | Deleted | Revised | Net change |
|---|---|---|---|---|
| 120 LF | +30 LF | −10 LF | 140 LF | +20 LF |
Revised quantity = 120 + 30 − 10 = 140 LF. Preserve the 30 LF addition and 10 LF deletion as separate records even when the summary shows a net increase of 20 LF.
Apply the guide to your bid package
Compare this checklist with your current drawings, specifications and agreed trade scope. For bid estimating support, send the relevant documents and note any assumptions you want reviewed. The fee and scope guide explains questions to confirm before authorizing an estimate.
See the illustrative deliverable layouts for workbook organization. The examples in this guide are educational inputs, not verified client results or a substitute for the project team's design and bid decisions.
Discuss an estimating requestReferences and further reading
These publisher resources provide background on the named tools or classification methods. They do not establish the requirements for a particular bid set or certify this estimate.