Guide · Bidding and tendering · 4 min read · Updated September 18, 2026
Tender vs. construction drawings: how to find what changed after award
You priced one set of drawings and you will build from another. The differences between them are where scope, cost, and schedule arguments start, so find them early and write them down.
Tender drawings are the set bidders price; construction drawings, issued for construction (IFC), are the set the contractor builds from. They often differ because addenda, tender answers, and design finished after the tender all land in the construction set, so compare the two sheet by sheet, record each difference with references on both sides, and raise the ones that change scope through the contract's change process before its notice periods run out.
Tender and construction drawings at a glance
| Tender drawings | Construction drawings | |
|---|---|---|
| Purpose | Price the work on a common basis | Build the work |
| Typical label | Issued for Tender, For Bid, Bid Set | Issued for Construction (IFC), For Construction |
| Level of detail | Enough to price; some details may still be developing | Complete for the work shown, including answers issued during the tender |
| Changed by | Addenda and tender clarifications before award | Revisions, instructions, and change orders after award |
| Contract role | Usually part of the documents the price rests on | The documents the contractor is instructed to build from |
In US practice the construction set should be the conformed documents: the construction documents with addenda and accepted alternates incorporated.[1] The Ontario Association of Architects puts it more strictly: the IFC set should be identical to the contract documents, and the risk is a set that leaves agreed changes out or quietly adds new ones.[2] On many projects, especially outside North America, the construction drawings are a further stage of design, so some difference is expected and the contract decides who carries it.
Why the construction set differs from the set you priced
- Addenda and answers to tender queries are folded in, sometimes with edits of their own.
- Design that was incomplete at tender is finished: details, coordination between consultants, and specialist design.
- Scope agreed during negotiation, such as value engineering, alternates, or omissions, is drawn in.
- The client asks for changes after award.
- Permit or authority comments require revisions.
- Errors are corrected, which can add scope without anyone calling it a change.
These are common sources of dispute. HKA's analysis of disputed North American projects found a change in scope on 27% of US and 35% of Canadian projects, and design errors on 20% and 31%.[10] Finding the differences early does not settle who pays, but it keeps the question inside the contract's time limits.
What each contract calls a change
| Contract | What a change is called | What to watch |
|---|---|---|
| JCT (UK) | Variation, instructed by the architect or contract administrator; called a Change in design and build forms | Valued at contract rates where the work is similar, otherwise at fair rates[3] |
| NEC4 (UK and international) | Compensation event, for example a project manager's instruction that changes the Scope | Notify within eight weeks of becoming aware of the event, or in most cases lose the claim[4] |
| AIA A201-2017 (US) | Change Order, Construction Change Directive, or order for a minor change | Claims generally start within 21 days of the event or of first recognizing it[11] |
| AS 4000 (Australia) | Variation directed by the Superintendent | The 2025 edition treats a direction that resolves a discrepancy between documents as a variation[5][6] |
| CCDC 2-2020 (Canada) | Change Order or Change Directive; a Supplemental Instruction changes neither price nor time | Report errors and inconsistencies you find, and do not proceed with the affected work[7] |
This is orientation, not legal advice. Read the notice and valuation clauses in your own contract, including any amendments.
How to compare the tender set with the construction set
- Fix the baseline. The baseline is what you priced: the tender drawings plus every addendum, tender answer, and agreed adjustment. Check which documents the contract actually names. In one thread on an NEC users' forum, a contractor had priced drainage at about 1.5 m deep and received construction drawings showing about 4 m; the first question was which documents the contract data listed as the baseline.[9]
- Align the two drawing registers. List matched, added, removed, and renumbered sheets. Added sheets often take a suffix, such as D6A, and a renumbered sheet can hide real change.[8] The drawing register template works for both sets.
- Compare every sheet pair, not just the clouds. Overlay the pairs or compare them side by side, discipline by discipline.
- Compare schedules, notes, and specifications line by line. A changed rating in a door schedule or a new specification clause can cost as much as a moved wall, and it is harder to see.
- Log each difference. Record the tender and construction references, what changed, the package affected, and the possible effect. The free tender-to-construction change log has the columns.
- Sort and act. Mark each difference as no effect, a clarification, or a possible change. Give notice of possible changes under the contract, send RFIs for unclear ones, and pass differences to the affected subcontractors so they can price or confirm them.
Why revision clouds are not enough
- Deletions are often not clouded. Washington State DOT's plans manual, for example, records deletions in the revision block instead of clouding them.[8]
- Heavily revised sheets may carry no clouds. The same manual calls for a replacement sheet when clouds would cover more than half of it.[8]
- One change ripples. A moved opening can affect architectural, structural, and mechanical sheets that were not revised together.[8]
- Revision blocks describe what the designer chose to describe, not every difference on the sheet.
- Specifications and schedules change without a cloud on any drawing.
Example from a published review
In Groundbook's mixed-use residential review, the set had moved through permit and tender revisions, and two structural schedules carried different requirements without a clear governing version. The same problem appears between a tender set and a construction set: if nobody records which version governs, different teams price, detail, or install against different requirements.
Where Groundbook fits
Groundbook AI's drawing version comparison, available to beta users on request, takes the two PDF sets, matches sheets by number, lists added and removed sheets, and organizes the changes for review with the source on each side. You can also run a full document review of the construction set itself. It does not price changes or decide entitlement; your team verifies each difference and decides what to raise.
Sources
- AIA Contract Documents, B101-2017 instructions, section 4.1.1.14 (conformed documents)
- Ontario Association of Architects, Issued for Construction Documents
- Ramskill Martin, Back to basics: variations and change under the JCT
- NEC, Compensation events: an introduction for new NEC users
- Turtons, How to claim a variation under AS 4000
- HWL Ebsworth, The new and improved AS 4000:2025 general conditions of contract
- CCDC 2-2020, Stipulated Price Contract, definitions and GC 1.1
- Washington State DOT, Plans Preparation Manual M 22-31, Appendix 5
- ReachBack NEC forum, Tender vs construction drawings (NEC3 Option A)
- HKA, Designs on better outcomes: CRUX insight on time and cost overruns
- AIA Document A201-2017, General Conditions of the Contract for Construction, Article 7 and section 15.1.3
Keep reading
Related pages
Questions, answered
Frequently asked questions
Is the contractor paid for differences between tender and construction drawings?
It depends on the contract and on what the tender set showed. A change instructed after award is usually valued as a variation, change order, or compensation event, but completing details that the tender set already implied may not be. Most contracts also set notice periods, so raise differences promptly.
What is a conformed set?
The contract documents with every addendum, accepted alternate, and agreed change incorporated. In US and Canadian practice it is often issued as the construction set, so it should match what the contract says was priced.
Who should compare the sets, the general contractor or the subcontractors?
Both. The general contractor needs the full list to manage notices and the owner, and each subcontractor knows its own scope best and should confirm the differences that affect it.
What if the construction set has no revision clouds?
Compare every sheet. Clouds show what the designer chose to mark; a full comparison finds deletions, schedule edits, and changes that were never clouded.
How is this different from reviewing an addendum?
Addenda change the tender documents before award, and every bidder sees them. The construction set arrives after award, only the awarded contractor works from it, and differences go through the contract's change process.
Can Groundbook compare two drawing sets?
Yes, in a beta available on request. It matches sheets, lists added and removed sheets, and organizes changes with their sources for your team to verify. It does not calculate the cost of a change.
Compare your construction set with the set you priced
Set up a review yourself, or book time to talk through your project.