As-built drawings and redlines: from the mark-up in the field to the drawing the plant runs on
What an as-built drawing is and what it is not, what a redline has to carry to be usable, the seven steps from a field mark-up to an issued revision with a check at each end, which documents go as-built and what changes on each, and why as-builts continue for the life of the plant rather than ending at handover.
Key takeaways
- An as-built drawing shows what was built. The issued-for-construction drawing shows what was intended. The plant is operated, maintained and modified from the first, and a plant that only has the second is run from drawings that are wrong in ways nobody has written down.
- A redline is the raw material: a hand mark-up in red on a print of the current revision, clouded, with what was done, why, who and when. It is not a document the plant runs on, and nothing is built or maintained from it.
- The redline becomes an as-built through a path with checks at both ends: the engineer confirms the mark-up is what was built and was authorised, the drafter incorporates it at a new revision, the engineer verifies the drawing against the mark-up, and document control issues it and withdraws the old revision.
- As-builts are not a project close-out task. Every modification for the life of the plant produces redlines, and management of change is not closed until they have been drawn up.
- The usual failure is not bad drafting. It is redlines made and never collected, sitting in a ute, a site office or a box, while the plant runs on the revision they corrected.
A fitter isolates a pump from the P&ID and finds a bypass line the drawing does not show. An electrician lands a cable on the terminal the loop diagram gives and it is the wrong one, because the panel was rewired at commissioning and the mark-up is in a folder in a site office that was demobilised in 2021. A design for a new feeder is drawn from the single line and the breaker it needs was replaced with a bigger frame three years ago. Each of those is the gap between what was intended and what was built, and that gap is exactly where the problems are.
As-built drawings close the gap. The issued-for-construction drawing says what was meant to be built. The redline says where the field differed. The as-built incorporates the redlines at a new revision and becomes the drawing the plant runs on. The idea is simple and the path from red ink to an issued revision is where it fails, because the path has seven steps and most of them belong to people who have other things to do.
This guide sets out what an as-built is and what it is not, what a redline has to carry to be usable, the path from the mark-up to the register with a check at each end, which documents go as-built and what typically changes on each, how as-builts are produced during a project and after every modification for the rest of the plant's life, and where the process breaks. It sits beside the document control guide, which covers the register and the states a drawing passes through.
What an as-built is, and is not
A controlled drawing passes through states, and the two that matter here are issued for construction and as-built. The first is the design, approved and issued to build from. The second is reissued after the work, at a new revision, to show what was built, verified by the discipline engineer against the field mark-ups. The plant is operated and maintained from the as-built, every later modification starts from it, and the issued-for-construction revision is superseded the day it is issued and never used again.
The words vary by discipline and contract. The table sets out the ones in use and what each means where it is used precisely. The one to be careful of is record drawing, which in some contracts means a drawing the designer prepared from the contractor's mark-ups without checking them in the field. That is a redline that has been drafted, not an as-built, and the plant should know which it holds.
| Term | What it means |
|---|---|
| Redline | A hand mark-up on a print showing what differs from the drawing. Raw material, not a document the plant runs on |
| As-built | A reissued drawing incorporating the redlines, showing what was built. The revision the plant runs on |
| As-constructed | The same thing, used on civil and structural work and in some contracts. Not a different state |
| Record drawing | The owner's term for the as-built held in the archive. In some contracts a drawing prepared by the designer from the contractor's redlines, with a note that it was not verified in the field |
| As-installed | Vendor and electrical usage for the as-built of a package or an installation |
| Issued for construction | What was intended. Superseded by the as-built, never used after it |
What a redline has to carry
A redline is a hand mark-up on a print, and it is only useful if the drafter can incorporate it without going back to the field and the engineer can check it without guessing. The rules in the table are what make that possible, and the first and the fourth are the ones most often broken. A mark-up on an old revision creates a second change nobody asked for, because the drafter has to work out what in the mark-up is new and what the old print was already missing. A mark-up with no source, no punch item, change number or design query behind it, is a modification that nobody reviewed, found at the drafting stage, and the question of whether it should have been made at all is asked a year late.
The last rule matters too. A redline records what was built. A better idea for how it could have been built is a change request through management of change, and a drafter who incorporates a suggestion as if it were built has put something on the drawing that is not in the field.
| Rule | Why |
|---|---|
| The base | A print of the current issued revision, with its number and revision visible. A mark-up on an old revision creates a second change nobody asked for |
| The cloud | Every change clouded, so the drafter finds all of them and incorporates nothing that is not clouded |
| The words | What was done, in the same terms the drawing uses: the tag, the size, the rating, the routing. Not 'as per site' |
| The reason | The punch item, change number or design query that authorised it. A redline with no source is a modification with no review |
| The author and date | Who marked it and when, so a question has somewhere to go |
| One per drawing | A change that touches three drawings is three redlines, each closed on its own |
| Nothing speculative | Only what was built. A suggestion for a better arrangement is a change request, not a redline |
Red ink on a current print, clouded, with what, why, who and when. Anything less is a sketch.
From the mark-up to the register
The path has seven steps and two checks, one at each end of the drafting. The first check, before drafting, is that the mark-up is what was built and was authorised. The second, after drafting, is that the new revision matches the mark-up, line by line, so that an error in drafting does not become the drawing the plant runs on. Between them the drafter does the work, and the revision note says what changed and why, with the source, so that the history of the drawing can be read from its title block.
The collection step is the one that decides whether the others happen at all. Redlines are made by people in the field during the work, and if nobody collects them against a register, by drawing number, with a status per drawing, they stay where they were made. The register is small: the drawing number, whether a redline exists, who holds it, and where it is on the path. It is kept by commissioning during a project and by document control afterwards.
1Mark up
The person who made or found the difference
Clouds the change on a print of the current revision, in red, with what was done, the date and their name
A redline, one per drawing
2Collect
Commissioning or the document controller
Gathers every redline against a register, by drawing number, so none stays in a ute or a site office
The redline register, with a status per drawing
3Check
The discipline engineer
Confirms the mark-up is what was built, that it was authorised (a punch item, a change, a design query) and that nothing is marked that was not done
A checked redline, or a query back to the field
4Draft
The drafter
Incorporates the redline into the native drawing at a new revision, with the revision note saying what changed and why
A draft as-built revision
5Verify
The discipline engineer
Checks the new revision against the redline, line by line, and signs the title block
An approved as-built revision
6Issue
Document control
Issues the revision to the register, withdraws the superseded revision from every point of use, and tells the people who hold copies
The as-built on the register, the old revision marked superseded
7Close
The project or the change owner
Closes the redline against its source: the punch item, the change or the design query
A closed redline, traceable to why
→ Red ink is raw material. Nothing is built or maintained from it
The plant runs on the drawing from here
| Step | Who | What they do | What it produces |
|---|---|---|---|
| Mark up | The person who made or found the difference | Clouds the change on a print of the current revision, in red, with what was done, the date and their name | A redline, one per drawing |
| Collect | Commissioning or the document controller | Gathers every redline against a register, by drawing number, so none stays in a ute or a site office | The redline register, with a status per drawing |
| Check | The discipline engineer | Confirms the mark-up is what was built, that it was authorised (a punch item, a change, a design query) and that nothing is marked that was not done | A checked redline, or a query back to the field |
| Draft | The drafter | Incorporates the redline into the native drawing at a new revision, with the revision note saying what changed and why | A draft as-built revision |
| Verify | The discipline engineer | Checks the new revision against the redline, line by line, and signs the title block | An approved as-built revision |
| Issue | Document control | Issues the revision to the register, withdraws the superseded revision from every point of use, and tells the people who hold copies | The as-built on the register, the old revision marked superseded |
| Close | The project or the change owner | Closes the redline against its source: the punch item, the change or the design query | A closed redline, traceable to why |
Which documents go as-built
Any document the plant will be operated, maintained or modified from, which is most of the engineering set. The table lists the usual ones, what typically changes on each between the issued-for-construction revision and the field, and who owns the as-built for content. Two are often forgotten. The cable schedule, because the cables as pulled differ from the design in size, route and length on every project, and the schedule is what the next cable is sized from. And the control system configuration, which is as-built as a backup taken at the end of the site acceptance test rather than as a drawing, and is the baseline every later change is made from.
| Document | What typically changes | Owner |
|---|---|---|
| P&IDs | Added or deleted instruments, bypasses, drains and vents, changed valve types and line sizes | Process engineering |
| General arrangements and layouts | Equipment positions, platform and access changes, pipe and cable routes | Mechanical and civil |
| Loop diagrams and schematics | Terminal numbers, cable cores, junction boxes, changed IO addresses | Electrical and control |
| Single line diagrams | Breaker and feeder changes, protection settings, added distribution | Electrical |
| Cable schedules | Cable sizes, routes and lengths as pulled, spare cores | Electrical |
| Instrument index and IO list | Tags added, deleted or re-ranged, the addresses as commissioned | Control |
| Control system configuration | The logic, the alarm settings and the HMI as tested at the SAT: a backup, not a drawing | Control |
| Datasheets | The equipment actually supplied, where it differed from the specified item | The discipline |
| Civil and structural | Footing levels, set-out, steelwork modified on site | Civil and structural |
During the project and for the rest of the plant's life
On a project the as-builts are produced as each system reaches mechanical completion, not at the end. The people who built the system are there, the differences are fresh, and the commissioning team needs the as-built P&ID and loop diagrams for the loop checks and the SAT. A project that leaves as-builts to close-out produces them from memory, after the contractor has demobilised, by the people with the least interest in getting them right. The as-built set is on the handover list, and operations do not accept a system without it.
After handover the plant keeps changing, and the as-builts have to keep up. Every modification produces redlines on the drawings it touched, and the management of change is not closed until they have been drawn up, issued and the old revisions withdrawn. The document register lists the drawings by the equipment tags they describe, which is how the list of drawings to redline is made from the record rather than from memory. A site where the as-builts stop at handover is run, five years later, from drawings that are wrong in every place the plant was improved.
A change is not finished when the plant runs. It is finished when the drawing says what the plant is.
Where it breaks
- Redlines made in the field and never collected, so the as-builts are drafted from memory or not at all.
- Mark-ups on old revisions, so the drafter cannot tell the new change from the old gap.
- Mark-ups with no source, so modifications nobody reviewed reach the drawing a year later, or are quietly dropped.
- As-builts left to project close-out and produced by a demobilising contractor from what they remember.
- Record drawings prepared from the contractor's mark-ups without field verification, and held as if they were verified.
- The as-built revision issued but the superseded prints left on the wall of the switchroom and in the folder in the cabinet.
- The control system backup not taken at the end of the SAT, so the as-built configuration is whatever is running.
- As-builts treated as a project deliverable, so the first modification after handover is never drawn up and the set is out of date within the year.
Common questions
What is an as-built drawing?
A drawing reissued after construction, commissioning or a modification to show what was actually built, incorporating the field mark-ups made during the work, as distinct from the issued-for-construction revision that showed what was intended. It carries a new revision with a note saying it is as-built, is verified by the discipline engineer against the mark-ups, and is the revision the plant is operated, maintained and modified from.
What is a redline drawing?
A print of the current issued drawing marked up by hand, conventionally in red, to show where what was built differs from it. Each change is clouded and annotated with what was done, the reason it was authorised, who marked it and when. A redline is the record from which the as-built is drafted. It is raw material, not a controlled document, and nothing is built or maintained from it.
What is the difference between as-built and record drawings?
Often nothing, and the difference is worth checking in the contract. On most sites a record drawing is the owner's term for the as-built held in the archive. In some construction contracts a record drawing is one the designer prepares from the contractor's redlines without verifying them in the field, and it carries a note saying so. As-constructed and as-installed are the same state under other disciplines' names. Whatever the word, the question is whether someone verified the drawing against what was built.
Who is responsible for as-built drawings?
The person who made or found the difference marks it up. The contractor or the commissioning team collects the mark-ups against a register. The discipline engineer checks each one is what was built and was authorised, and later verifies the drafted revision. The drafter incorporates it. Document control issues the revision and withdraws the old one. After handover the owner's engineering function owns the drawings for the life of the plant, and every modification repeats the path. A contract that says the contractor provides as-builts has to say what that means and who verifies them.
When should as-built drawings be produced?
At three points. During construction, as each system reaches mechanical completion, so the redlines are made while the people who built it are still there. At handover, when the as-built revisions are part of what operations accept. And after every modification for the life of the plant, where the management of change is not closed until the drawings have been reissued. The first and third are the ones projects and sites skip, and both produce the same result: a plant run from drawings that are known to be wrong.
Which drawings need to be as-built?
Any drawing from which the plant will be operated, maintained or modified, which in practice means the P&IDs, general arrangements and layouts, loop diagrams and schematics, single line diagrams, cable schedules, the instrument index and IO list, datasheets where the supplied item differed, and the civil and structural drawings where set-out or levels changed. Control system configuration is as-built too, as the backup taken at the end of the site acceptance test rather than as a drawing.
Key terms
Plain-language definitions from our glossary for the concepts this article leans on.
Standards and further reading
- IEC 81346-1:2022 Industrial systems, installations and equipment: structuring principles and reference designations (IEC)
- IEC 61082-1:2014 Preparation of documents used in electrotechnology, part 1: rules (IEC)
- ISO 7200:2004 Technical product documentation: data fields in title blocks and document headers (ISO)
- ISO 15489-1:2016 Records management: concepts and principles (ISO)
- IEC 62337:2012 Commissioning of electrical, instrumentation and control systems in the process industry: specific phases and milestones (IEC)
Related case studies and tools
- Operational readiness for a new plant asset (case study)
Related reading
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