As-built drawings

No project is built exactly as designed. Services get rerouted, setout moves, variations add or remove work and RFIs change details. As-built drawings capture those changes so the final record matches what is in the ground and in the walls.

The usual process starts on site. Trades and site engineers mark changes on a set of construction drawings as the work happens, often in red pen, which is where the term red-lines comes from. At the end of each trade's scope, those markups go back to the drafter or designer, who updates the CAD files or model. For civil works and underground services, a surveyor often picks up the actual positions and levels so the WAE drawings show real coordinates and depths. Each revision should be dated and tied back to the RFI, variation or site instruction that caused it.

Most head contracts and subcontracts require as-built or WAE drawings as part of the handover documents, and many make them a condition of practical completion or of releasing retention. Common requirements include:

• Building services. Mechanical, electrical, hydraulic and fire services as-builts for the owner and facility manager.

• Structure and architecture. Updated plans where the built layout differs from IFC.

• Civil and stormwater. WAE plans with surveyed levels, often required by councils before accepting assets or releasing bonds.

• Utilities. Water, sewer and electrical authorities generally require WAE information before they take over new assets.

The specification usually sets the format, such as PDF and native CAD or BIM files, and who must certify them.

IFC drawings show what the designer intended. Shop drawings show how a trade will fabricate and install its part. As-built drawings record what was actually done once the work is finished.

In a BIM project the same idea applies to the model. The as-built or record model is updated to reflect installed conditions so the owner can use it for facilities management.

The practical difference shows up years later. When a tenant wants to cut a new penetration or a plumber needs to find a buried valve, nobody looks at the IFC set or the shop drawings. They look at the as-builts, and if those are wrong the owner pays for exploratory work, damaged services or a redesign.

• Leaving it to the end. Trying to reconstruct changes from memory at handover produces inaccurate drawings. Mark up as the work is done.

• No survey for buried services. Without surveyed positions and depths, underground as-builts are guesswork.

• Ignoring subcontractor scope. Each trade should provide its own as-builts, and the head contractor needs to chase and check them.

• Unchecked drawings. A quick walk through with the drawings in hand catches obvious errors before they are handed over.

• Wrong format. Delivering scanned PDFs when the contract requires native CAD or model files can delay final payment.