A specification for a 3D survey fits on one page, but it must fix 8 points: the exact scope, the level of development (LOD), the expected accuracy, the deliverables and their formats, georeferencing, access constraints, lead times and acceptance criteria. If any one of these is missing, the offers you receive will not be comparable, and the lowest price will often be the one that understood the least of what you asked for. This guide goes through each point, with the usual values for a building in French-speaking Switzerland, then gives you a checklist to copy and paste into your next tender.
Want a budget figure first? Our quote configurator prices your project in 2 minutes; the detailed ranges are in our article How much does a 3D survey cost in French-speaking Switzerland?.
Why a specification, even for a “small” survey
When an architecture practice or a property management firm sends out a request that simply reads “3D survey of building X, please quote”, it receives offers ranging from one to three times the price. Not because the providers are dishonest, but because each one has filled in the blanks in their own way: one prices a raw point cloud, another an ArchiCAD LOD 300 model with an SIA 416 area schedule. Both are right; the request did not decide.
A one-page specification is enough to make offers comparable line by line, as in any conventional tender. Here is what it must contain.
The 8 points your specification must fix
1. The exact scope: interior, exterior, attic, basement
This is the first source of price variation. Specify:
- Interior: every room, or only certain floors? Are occupied flats included?
- Exterior: all four façades? The roof (from the ground, by drone, or not at all)? External works and the land (a strip of a few metres, or the whole plot)?
- Attic and basements: often left out of the request, then demanded at delivery. If they are inaccessible or cannot be visited, say so; the provider will make an assumption or a reservation.
- Plant rooms, ducts, crawl spaces: include them explicitly if your project needs them (MEP, asbestos removal, compliance upgrades).
Attach a site plan and, if you have them, the old drawings: even when wrong, they help size the job.
2. The expected LOD, and for what use
The LOD (Level of Development, 100 to 400) defines what the model contains. In practice, in French-speaking Switzerland:
- LOD 200: volumes and main elements; enough for a feasibility study or a sales file.
- LOD 300: precise geometry of every element; the standard for a conversion project and a building permit application.
- LOD 350–400: interfaces between elements, openings and recesses; for construction and MEP coordination.
The right reflex: state the use (“model intended for a conversion project with a building permit application”) rather than a LOD on its own. A serious provider will confirm or correct the level. To choose with full knowledge, see our guide LOD 100–400: which level of detail for your model?.
3. Accuracy and tolerances, in centimetres
Two separate figures, often confused:
- Point cloud accuracy: a terrestrial laser scanner measures to ±2–5 mm per point. This is the raw material; it is rarely the problem.
- Modelling tolerance: the accepted deviation between the model and the cloud. An old building has neither plumb walls nor level slabs; the model simplifies. Usual values: ±1 cm on new or regular structural elements, ±2 cm on older buildings, up to ±3 cm on heavily deformed surfaces (vaults, roof timbers).
Require the offer to state this tolerance, and require the provider to be able to prove it at delivery (see point 8).
4. Deliverables and their formats
List precisely what you want to receive, with format and version:
| Deliverable | Format | To specify |
|---|---|---|
| Point cloud | E57 (open standard) | Density, split by floor, coloured or not |
| BIM model | RVT (Revit) or PLN (ArchiCAD) | Software version (e.g. ArchiCAD 28), template supplied or not |
| Interoperable export | IFC (2x3 or 4) | Useful for engineers and building management systems |
| 2D drawings | DWG / PDF | Plans, sections, elevations: scale and level of annotation |
| Areas | SIA 416 report | Schedule per room and per floor (SP, SU, etc.) |
Also state whether you want furniture and MEP equipment included, and who owns the source files at the end of the engagement (recommended answer: you).
5. Georeferencing: LV95/LN02 and surveyor control points
By default, many surveys are delivered in a local coordinate system: perfectly usable for an interior conversion, insufficient as soon as the project touches the plot, its boundaries or a building permit application.
If your project requires it, ask for georeferencing in MN95 (LV95 coordinates) with LN02 heights, fixed on control points supplied by a licensed land surveyor (3 well-distributed points are usually enough). Specify who commissions the surveyor, you or the provider, and include that cost when comparing offers.
6. Access constraints and occupancy
The provider is also pricing its days on site. State:
- Is the building occupied (tenants, shops, offices)? Who arranges access to the flats, and with how much notice?
- Who hands over the keys, and to whom (property manager, caretaker, owner)?
- Are there restricted areas (roof without guardrails, rooms containing asbestos, boiler room)?
- Any imposed hours (scanning a shop outside opening hours, for example)?
A building with 15 occupied flats may need two or three visits instead of one: that is price and lead time. Saying so from the outset avoids change orders.
7. Lead times, separating fieldwork from modelling
Ask for two dates, not one: the date of on-site acquisition (a team scans roughly 400 m² per day: one day for a detached house, a few days for an apartment building) and the date of model delivery (modelling takes most of the lead time, around 100 m² per day per modeller). Orders of magnitude, all in: 7 to 9 working days for a detached house, 11 to 14 working days for an 850 m² building, 16 to 20 working days for a 1,500 m² apartment building; beyond that, the team scales with the project to hold the schedule. If an external deadline exists (permit submission, signing, co-owners’ meeting), write it down: it separates the providers who can deliver from those who merely promise.
8. Acceptance criteria for the model
This is the point most often missing from tenders, and the most profitable. Include a clause along these lines:
“The model will be checked by overlaying it on the point cloud. Deviations beyond the stated tolerance will be corrected at no extra charge. The area schedule will be spot-checked on [X] rooms. Delivery is deemed accepted after written approval by the client, no later than [X] days after receipt.”
Without acceptance criteria, “delivered” means “sent”. With them, it means “compliant”. Our article Checking that a scan-to-BIM model is fit for use details the checks to carry out on receipt, even if you are not a BIM specialist.
Questions to ask the provider
Beyond the specification, three questions during the tender reveal a great deal:
- “Who does the modelling, and where?” Scanning is sometimes local while modelling is subcontracted without oversight. That is not disqualifying in itself, but you need to know who answers for quality and who corrects deviations. At Studio BIM, every model is checked and approved by our architects before delivery.
- “What is your quality control before delivery?” A good answer cites, at minimum, a systematic model-to-cloud overlay and a review by a second person. “We check that everything lines up” is not quality control.
- “Do you carry professional liability insurance, and for how much?” A survey error can propagate all the way to construction. Ask for the certificate, as you would with any other consultant.
Other useful questions: references on comparable buildings, equipment used (static scanner, mobile scanner, drone), and what happens if a room turns out to be inaccessible on the day of the scan.
The common mistakes we see in tenders
- Comparing a point cloud with a model. An offer at CHF 3’000 for a raw cloud and an offer at CHF 8’000 for scan + LOD 300 model are not answering the same question.
- Reusing an existing point cloud without auditing it. We saw this on a barn in the canton of Vaud: the owner had an E57 file and asked for “just” the modelling. The cloud was too patchy to be used, and a new survey was needed. Have the file audited before tendering on that basis.
- Forgetting georeferencing, then discovering the need when assembling the permit application. Realigning a model after the fact costs more than 3 surveyor control points at the outset.
- Asking for LOD 400 everywhere “to be safe”: you pay for a level of detail the project will never use. LOD is chosen by use, sometimes by package (structure at LOD 300, finishes at LOD 200).
- Making no provision for acceptance: without written criteria, the balance of power at delivery sits with the provider.
The specification to copy and paste
Subject: 3D survey and BIM modelling, [address, municipality] 1. Scope: [floors, interior/exterior, façades, roof, attic, basement, land: X m strip] · building [occupied/vacant], access via [property manager/caretaker] 2. Use & LOD: model intended for [conversion / sale / operation], LOD [200/300/350]; provider’s proposal welcome 3. Accuracy: cloud ±5 mm; modelling tolerance stated in the offer (expected: ±1 to 2 cm depending on elements) 4. Deliverables: E57 cloud · model [RVT version X / PLN version X] · IFC export · plans, sections and elevations in DWG/PDF · SIA 416 area schedule · source files owned by the client 5. Georeferencing: [local / MN95-LV95 + LN02 on 3 control points from a licensed land surveyor, commissioned by X] 6. Constraints: [hours, restricted areas, notice to tenants] 7. Lead times: acquisition before [date] · model delivery on [date] · external deadline: [permit submission / signing] 8. Acceptance: model-to-cloud overlay, correction of out-of-tolerance deviations at no extra charge, written approval within [10] days Attachments required with the offer: comparable references, professional liability certificate, name of the person responsible for modelling, description of quality control
FAQ
Is a specification needed for a small building (detached house, flat)? Yes, in a short version: scope, use, deliverables, lead time. Even for a detached house, the difference between “cloud only” and “LOD 300 model with SIA 416 areas” doubles the price.
How much does a 3D survey with a BIM model cost? From CHF 1’350, which is the minimum order for a survey + modelling (CHF 740 for modelling only on a supplied cloud, CHF 610 for a scan only). As a reference point, an 850 m² building in survey + modelling comes to around CHF 5’350, or roughly CHF 6.30/m²; the rate decreases as floor area increases. Detailed ranges by floor area and by product are in our pricing article, and the configurator prices your case in 2 minutes.
Can I ask for Revit and ArchiCAD in the same tender? Yes, but choose one main format (the one your practice uses) and ask for IFC alongside. Requiring both native formats increases the price with no real benefit.
Is LV95 georeferencing mandatory? No. It becomes so in practice as soon as the file touches the cadastre or a building permit application. For a strictly interior conversion or a sales file, a local system is enough.
Who should own the source files? You, as the client: write it into the specification. A provider who keeps the source files ties you to them for every future change.
Tender with a budget in mind
A precise specification gives you comparable offers; a budget figure tells you which ones are serious. Our configurator gives you both: an indicative price in 2 minutes, based on our public rate card, the same one we use for our quotes.