As-Built BIM for Renovation: De-Risking Existing Buildings

How to scope an existing-building survey and BIM model for renovation, record uncertain areas and check the information before design.

Spetia Engineering·February 1, 2026·2 min read
Discuss your project
Residential exterior with timber accents and planting
Existing residential building exterior with timber accentsTopic illustration
On this page

Overview

  • Check existing records against measured site information before designing alterations.
  • Capture the areas and interfaces that the renovation depends on; a full-building survey is not always necessary.
  • Record survey dates, tolerances and concealed areas so designers know what they can rely on.

A renovation needs a dependable picture of what is already there. Record drawings, site measurements and scan data can each help. The team needs to know where they agree and where information is missing.

Check the existing records

Look for later fit-outs, rerouted services and changes to structural openings. Compare critical locations with current survey information. Keep reliable record information, but label anything that has not been verified.

Survey what the new design depends on

  • Identify the proposed work area and its connections to the rest of the building.
  • Specify the elements, geometry, attributes and tolerances needed for each design decision.
  • Record occluded spaces and concealed services. Agree further investigation where a design relies on them.
  • Check installation clearances and critical interfaces separately before fabrication.

Scope the existing-conditions model

Spetia can prepare a survey-based BIM model for the agreed renovation scope. Share the record drawings, available scans and proposed alterations. We will identify the inputs and checks needed before confirming deliverables and timing.

Technical references

Sources for the definitions and design context discussed here. Check the applicable edition and project requirements before using them in design.

  1. 01
  2. 02

Frequently asked questions

What is as-built BIM?+
It is a model intended to represent the recorded existing or constructed condition. Its reliability depends on the survey and records used, their date, the modeled scope and the checks completed. The label alone does not guarantee accuracy.
Why not just use the existing drawings for a renovation?+
Record drawings may not include later changes to walls, services or structure. A survey-based model helps identify differences before design progresses. It still has limits: occluded areas, concealed services and survey tolerances need to be recorded, with further investigation where necessary.
How detailed should a renovation model be?+
Specify the information needed for the alterations and their interfaces. A context area may need less detail than a new equipment connection. Set tolerances and verification requirements separately from LOD.

Keep reading

Leica HDS-3000 terrestrial laser scanner on a tripod
Scan-to-BIM

Scan-to-BIM Cost Per Sqft: Scope & Quote Guide

Laser-scan cutaway showing the rooms and walls of Tudor Place
Scan-to-BIM

Point Cloud to Revit: The Scan-to-BIM Workflow Explained

Structural building model showing reinforcement and framing
BIM & VDC

BIM LOD 100 to 500 Explained: What Each Level Actually Means

Image: Tudor Place interior laser scan, CyArk, CC BY-SA 3.0. Resized and cropped. Not a Spetia project.

Image: Leica HDS-3000 laser scanner, David Monniaux, CC BY-SA 3.0. Resized and cropped. Not a Spetia project.