Expert article
The digital twin: not the model but the history
A design model shows how it is meant to turn out. A digital twin shows how it did turn out — and how it looked on every day before that.
Expert article by Open Experience GmbH. · As of: September 2026
What is a digital twin in construction?
A digital twin is the continuously updated digital representation of a real building. It consists of design data — geometry, specified finishes, costs, dates — and of actual data from the site: 360° captures, photos, webcam and sensor data, inspection and defect processes. What sets it apart from the BIM model is not the way it looks but the time axis: the twin is kept up to date and therefore also holds conditions that no longer exist today.
Legal framework: Germany (Civil Code BGB, construction contract rules VOB/B, fee schedule HOAI). Other countries have different rules, and contractual agreements take precedence over the standard periods named here.
BIM model, point cloud, digital twin
The three terms are often used interchangeably and describe very different things.
| What it is | Relation to time | What it is good for |
|---|---|---|
| *BIM model* | Intended state, one design status | Designing, tendering, coordinating |
| *Scan / point cloud* | Actual state, one point in time | Measurement, surveying the existing fabric, checking geometry |
| *Digital twin* | Actual state over time | Tracing, checking, proving, operating |
A twin that is not kept up to date is a scan. A twin with no link to the design is a collection of pictures.
What the twin is made of
The data sources differ in effort and in how much they contribute. For the construction phase, four of them carry most of the load.
- 360° walkthroughsThe core: a complete capture of the accessible area at fixed points in time, located on the floor plan or in the model.
- Photos and defect processesThe targeted addition — close-up shots with a description, a deadline and someone responsible.
- Stationary sourcesA site camera and weather data supply the history even when nobody is on site.
- Design dataThe floor plan or IFC model gives the whole thing its structure — without it, all that remains is a chronology without order.
What the twin is needed for during the construction phase
The benefit does not come from the display but from the four questions it answers — questions that can otherwise only be settled by memory or by opening up a building element.
- What did it look like before it was closedService runs, waterproofing, reinforcement: the most common reason why somebody has to open a wall later on.
- When was what installedThe series of captures shows the date of installation — the basis for notices of obstruction, variation claims and invoice checking.
- Does actual match intendedElement present, in the planned position, in the planned detail — checkable on screen, without travelling.
- What belongs in the as-built fileAfter acceptance the history becomes the documentation that is actually used for refurbishment, maintenance and warranty.
An example: checking invoices
One use case makes the difference tangible. Traditionally an interim invoice is checked against measurement and memory, and in case of doubt with an extra visit to site. With an actual condition that is kept up to date, the capture of the same area from the same week sits next to the invoice item. The discussion then shrinks to the cases where there really is disagreement.
Taken further — and a subject of research, not part of the delivered scope — progress can be derived from the images themselves. Today the gain is plainer: the picture sits next to the item.
What a digital twin is not
Not self-sustaining
Without a fixed walkthrough rhythm no history emerges, only a gap with two edges.
Not real-time control
The twin shows the last condition captured — not the present moment.
No substitute for measurement
360° captures do not produce dimensions fit for a contract.
No substitute for expert inspection
Whatever calls for touching, measuring or opening up remains a visit to site.
Not a data graveyard
Captures without positioning and without evaluation create costs and no benefit.
But
It is the only form of documentation that also contains what nobody was looking for.
Data protection and access
A complete capture also records people at work — which makes it personal data. That is manageable, but not a side issue: people and faces are pixelated automatically before the capture moves into the project store; access is granted per project and per role; transmission is encrypted. What remains afterwards is the condition of the building — and that is exactly what should remain.
The twin is created on the normal site walk
DIGIBAU 360 is an attachment for a standard hard hat: a mini computer with a 360° camera, Wi-Fi, lighting and sensors for temperature and humidity. In manual mode you pick a point on the floor plan and take the capture; in automatic mode capture runs alongside without any input. The site walk that happens anyway thereby becomes the continuously updated actual condition.
Frequently asked questions
Do I need a BIM model for a digital twin?
No. Floor plans are enough to locate captures. An IFC model improves the allocation and allows positioning in three dimensions, but it is not a prerequisite.
How does the twin differ from photo documentation?
In completeness and rhythm. Photos show what somebody thought was important; a 360° walkthrough shows the room — including the places where nobody suspected a problem at the time of capture.
How large do the data volumes become?
They grow with area and frequency, but they stay manageable: resolution and compression can be set per project. Storage is central, not on end devices.
Is it only worthwhile above a certain project size?
The benefit depends less on size than on how much is closed up and how long the building will later be operated. Refurbishment of existing buildings often benefits more than new build.
What happens to the twin after completion?
It becomes part of the as-built documentation. For maintenance, refurbishment and warranty cases, the capture taken before closing up is often the only reliable source.
Is this the same as a digital twin in operation?
Related, but not the same. In building operation, live sensor data is added. During construction the value lies in the documented history — it is the basis on which an operational twin can later be built.
Sources and legal basis
The legal statements in this article are based on the primary sources listed below. The article is not a substitute for legal advice in an individual case.
The construction history you will need later.
45 minutes on a real project: a 360° walkthrough, the time axis and the jump back to the spot that was built over long ago.