Survey

Existing conditions modelling

CAD and PDF drawings, archive drawings, acceptance test reports: from the documents that already exist, completed with survey data where needed, the BIM model of the asset as it is.

At a glance

B1P Group's existing conditions modelling rebuilds an existing building or infrastructure asset in BIM from the documents available: CAD and PDF drawings, archive drawings, acceptance documents and building permits, completed where needed with the data of the survey carried out by the appointed surveyor. The model states for each element which source it comes from and how reliable it is, and it is the basis for refurbishment, technical due diligence and asset operation.

Definition

How does it differ from BIM modelling from survey data?

BIM modelling from survey data starts from a point cloud: it measures the asset as it is today, with known tolerances. Existing conditions modelling starts from the documents: it rebuilds the asset from what was drawn and approved, and uses the survey only where the documents are not enough or need confirming.

The two approaches are often combined: archive drawings provide structure, hidden building services and data that a point cloud cannot see; the survey confirms geometry and changes. The choice depends on the uses of the model and on the quality of the documents, and it is made before starting.

Deliverables: BIM model of the existing conditions in Revit or Civil 3D, IFC export, register of sources with the reliability of each element, list of the checks to carry out on site, 2D drawings from the model if requested
Standards: UNI 11337-4 for the levels of development of objects, ISO 19650, the client's information requirements
Sources: DWG and PDF drawings, scans of paper drawings, structural calculations and acceptance test reports, building and cadastral records, building services data sheets, survey data where available

Existing conditions modelling

Which documents are the starting point?

Everything that describes the asset: CAD drawings, PDFs of designs and variations, digitised paper drawings, structural calculations and acceptance test reports, building and cadastral records, manuals and data sheets of the building services. The first step is a list of the sources with their date and how up to date they are, because an asset changes over time and the documents do not always follow it.

Where documents are missing or contradict each other, we tell the client which measurements or which additional survey to ask the appointed surveyor for, only for the parts that the uses of the model require.

Existing conditions modelling

How is the uncertainty of archive drawings handled?

By stating it. Every element of the model carries a parameter with the source it comes from (drawing, report, survey, assumption) and a reliability level; the parts rebuilt by analogy are shown in a dedicated view. Whoever uses the model knows what can be taken as certain and what needs checking.

With the model we deliver the list of checks to carry out on site, ranked by importance for the intended uses: it is the cheapest way to arrive at a reliable model.

Existing conditions modelling

What is the existing conditions model for?

For the design phase of a refurbishment or an upgrade, which starts from a coordinated base instead of separate drawings; for technical due diligence and property valuations; for permit applications that require floor areas and uses; for asset operation and the digital property portfolio.

The level of detail is chosen from these uses: due diligence needs volumes, floors and areas; the detailed design of a refurbishment needs structure, partitions and the main building services.

Levels

Which model is needed, and from which sources?

Three typical configurations; the actual one is defined in the offer, based on the uses of the model and the documents available.

Model use	What it includes	Typical sources
Due diligence and valuation	Volumes, floors, areas and uses	Design drawings and cadastral records
Refurbishment design	Architecture and structure, partitions, openings and levels	Archive drawings, structural calculations, survey of the parts to be confirmed
Asset operation	Spaces, main building services and maintainable components with their data	Building services data sheets, manuals, acceptance documents

Related services

What does it combine with?

Frequently asked questions

Frequently asked questions on existing conditions modelling

Is a survey always needed?

No. If the documents are complete and up to date they are the starting point, and the survey only confirms the uncertain parts. The survey is carried out by the surveyor appointed by the client; B1P Group indicates what to measure and brings the data into the model.

What happens if the drawings do not match what was built?

Differences found in the documents or in the checks on site are recorded in the model and in the register of sources: the model follows the asset as it is, not as it was drawn.

Can we start from paper drawings?

Yes: the drawings are digitised, scaled and used as the base, and the model states that the source is an archive drawing.

In what format is the model delivered?

In Revit or Civil 3D depending on the type of asset, with IFC export and, if needed, 2D drawings extracted from the model.

Contact

Do you have an existing asset and only its drawings?

Send us the list of documents and tell us what you need to do with them: we will propose the level of detail, the checks to carry out and the timing.

Request a meeting B1P Group's BIM consultancy