As-Built Drawings vs New Construction Drawings
As-built drawings record a building that already exists, measured in the field, and their job is accuracy against reality. New construction drawings describe a building that does not exist yet, and their job is to be complete and unambiguous enough to build from. That difference changes everything downstream: as-builts are constrained by what you can physically access and verify, while construction drawings are constrained by what the design has actually decided. Neither converts cleanly into the other.
Clients frequently ask for one and describe the other. Someone renovating a building says they need construction drawings, when what has to happen first is an as-built record of what is there. Someone documenting a property says they need as-builts, when the actual requirement is a permit set for the work they intend to do. The distinction is worth getting right before any drafting work starts, because the input requirements diverge immediately.
As-built drawings: working backward from the building
An as-built set documents current conditions. The source is measurement, whether that comes from a field survey, a laser scan, an existing drawing verified in place, or some combination. The essential property is that every dimension traces back to something that was checked.
What constrains the work is access. Concealed structure, framing inside finished walls, and services above a hard ceiling cannot be measured without opening something up, so a competent as-built set marks what was verified and what was inferred rather than presenting both with equal confidence. In our practice, that distinction is the most useful thing on the sheet, because the next consultant needs to know which dimensions they can build from.
Typical uses are renovation planning, leasing and area calculation, code and compliance review, facilities records, and establishing a base for a design that will modify the building.
New construction drawings: working forward to a building
A construction set describes intent. Nothing is measured because nothing exists. Every dimension is a decision, and the set is complete when a builder can price and construct from it without having to guess.
What constrains the work here is not access but resolution of the design. A construction set cannot be finished ahead of the decisions it documents. If the stair detail is unresolved, the drawing cannot be, and drafting further will only produce work that has to be redone.
Typical uses are permitting, bidding, construction, and coordination between the architect, the engineers and the trades.
Where the two sets differ in practice
- Direction of truth. As-builts are judged against the building. Construction drawings are judged against the design intent.
- Tolerance. An as-built carries real world variation, out of square walls, floors that are not level, dimensions that do not add up. A construction drawing is drawn to nominal dimensions.
- Inputs. As-builts need field data. Construction drawings need decisions.
- Failure mode. An as-built fails by being wrong about what exists. A construction drawing fails by being incomplete about what is intended.
- Revision behavior. As-builts are revised when the building changes. Construction drawings are revised throughout design, which is most of their cost.
Renovation needs both, in order
This is the case that causes the most confusion. A renovation project needs an as-built record first, because the new design has to attach to real conditions, and then a construction set that describes the change. Attempting to draft the renovation without verified existing conditions produces drawings that fit a building nobody has measured, and in our experience the discrepancy surfaces on site, which is the most expensive place to find it.
Because the two sets are sequential rather than interchangeable, they are scoped separately. The as-built documentation is its own deliverable with its own inputs, and the construction set builds on top of it.
Which one to ask for
The test is a single question: does the building exist? If yes and you need a record of it, you need as-builts. If no, or if it exists and you are describing a change to it, you need construction drawings, and if you are describing a change you need both.
What the finished construction set has to contain is covered in what belongs in a permit set, and the accuracy question specific to as-builts is covered in drafting accuracy and tolerance standards.
Tell us whether the building exists and what you need the drawings to do and we will tell you which set you need and what it takes to produce it.