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What Are Redlines on Construction Drawings?

Last reviewed: November 2026

Redlines are markups drawn on a printed or PDF drawing, traditionally in red, that show corrections or changes to make. Engineers and architects redline check sets for drafters to pick up before issue, and contractors redline field sets to record how the work was actually built for as-built and record drawings.

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What you're looking at

Floor Plan Review, annotated

A review set with redline markups: clouded changes, notes, strike-outs, and questions back to the designer.

  1. 1Clouded area with a requested change
  2. 2Markup note from the reviewer
  3. 3Item struck out for removal
  4. 4Field verification request
Drawn by
Engineers, architects, checkers, and contractors in the field
Drawn on
Check prints, PDF sets, and the job site set
Common colors
Red to add or correct, green to delete, yellow highlight once picked up
Picked up by
The drafter or modeler who owns the file
Field redlines feed
As-built and record drawings at closeout
Required by
AIA A201 Section 3.11 and Division 01 record document sections

Definition

Redlines

A redline is an instruction to change a drawing. Until someone picks it up in the CAD or BIM file, clouds it, and issues the revised sheet, the drawing of record has not changed. Redlines come in two main kinds. Design redlines are a reviewer's corrections on a check set, such as move this tag, add a GFCI note, or this dimension string does not close. Field redlines are the contractor's marks on the job site set showing deviations, such as a rerouted conduit or a relocated valve, and they become the basis for as-built and record drawings.

In depth

Picking up redlines is a discipline of its own

The drafter works through the check print mark by mark, makes each change in the file, and highlights the mark in yellow so nothing is done twice or skipped. Marks that cannot be picked up as drawn, because the note conflicts with another sheet or the handwriting is unclear, get circled and sent back with a question.

The reviewer then back-checks by comparing the new plot against the marked print and confirming every highlight has a matching change. A single sheet can carry 30 marks after a thorough check, and the back-check is where a dropped mark gets caught.

After issue, a picked-up redline becomes a clouded revision

Once a set has been issued, changes made afterward are clouded and tagged with a revision number that matches the title block. Redlines picked up before the first issue usually are not clouded, because there is no prior issue to compare against.

After issue, every picked-up redline that changes the documents should map to a cloud, and every cloud to a line in the revision history. A dimension changed without a cloud is a silent revision the contractor will never look for.

Field redlines are the raw material for as-builts

On site, the contractor marks the set as work deviates from the drawings: a duct dropped below a beam, a panel moved to the opposite wall, a sleeve added through a slab. AIA A201 Section 3.11 requires the contractor to keep the documents at the site marked currently to record field changes, and project specifications often add requirements in Section 01 78 39, Project Record Documents.

Field redlines lose value quickly when they wait until closeout. Marks made from memory months later miss the depths, offsets, and concealed routing that an owner needs for the next renovation.

An unclear redline creates the error it was meant to fix

A mark that could mean add or delete, an arrow that lands between two tags, or a dimension written without units invites a guess. Good redlining writes the full note, points precisely, and uses the color convention the office agreed on.

Scanned hand markups bring their own problems, because a faint pencil note can drop out of the scan and red ink over red linework can vanish. PDF markups avoid most of that, though comments can stack on top of each other and markups can be left off the flattened PDF that gets sent.

Track redlines like any other open item

On a large set, a redline log lists each sheet, the number of marks, who picked them up, and who back-checked. Without a log, a sheet that was marked but never picked up looks identical to a sheet that came back clean.

Redlines that raise design questions should leave the drafting loop and go to the engineer or architect. A drafter should not settle a sizing or code question by picking the more convenient reading of a mark.

Examples

Redlines on a real project

  • 01

    An engineer redlines E-101 with 22 marks, including two receptacles to add in an apartment living room to meet NEC 210.52(A) spacing. The drafter picks up 21 and returns one with a question about a conflicting furniture layout.

  • 02

    A plumbing foreman redlines the field set to show a cleanout moved 3 feet east, and the change appears on the record drawings at closeout.

  • 03

    A checker marks a dimension string that does not add up to the overall dimension, and the drafter corrects both the string and the matching enlarged plan.

Tooling

Picking up redlines in your DWGs

Nomic reads scanned hand markups and PDF markups, edits the DWG files, clouds and tags every change, updates the title blocks, plots the set, and writes the transmittal. Marks it cannot read are flagged for a person instead of guessed.

Your team back-checks the revised sheets against the marked set, and the engineer or architect of record decides any mark that raises a design question.

Best AI for redline pickup

Best AI for Redline Pickup in 2026

FAQ

Frequently asked questions

Redlines are markups on a drawing that show changes or corrections. Reviewers redline check sets before issue, and contractors redline the field set during construction to record deviations from the drawings.

Redlines are the marks on a set. As-built or record drawings are the revised drawings produced after the field redlines are picked up into the CAD or BIM files at closeout.

A common office convention is red for additions and corrections, green for deletions, and blue for comments that are not to be drafted. Drafters often highlight marks in yellow once picked up. Conventions vary, so check the office standard.

It means making each marked change in the drawing file, highlighting the mark as done, and returning the revised sheet for a back-check against the marked set.

Keep reading

Related terms and workflows

What Is a Revision Cloud?

A revision cloud is a scalloped line drawn around the part of a sheet that changed, with a revision number or letter that matches the title block. It tells the reader what is different from the previous issue, and it leaves the rest of the sheet alone.

What Are As-Built Drawings?

As-built drawings are the marked-up set showing what was actually constructed, including every deviation from the original design. They are produced by the contractor during construction and handed over at closeout as part of the permanent record of the building.

What Is a Record Drawing?

A record drawing is a drawing the design professional issues at closeout, incorporating the changes and the contractor's field markups so the sheet shows the work as constructed. The contractor's marked-up set is the as-built information. The record drawing is the design team's compiled document. Specs often require both, and they are not interchangeable.

Best AI for redline pickup

Tools that carry scanned and PDF markups back into the DWGs, ranked.

As-built drawings

Field redlines drafted into record DWGs at closeout.

What Are Redlines on Construction Drawings? | Nomic