Construction quantity surveyor in the BIM era: Revit model quantities you can check
A construction quantity surveyor who works from a Revit model, an engineer or a registered building technician like Yaakov Avital, starts by checking the model, not by exporting tables. A model is built to design and to coordinate, so before you rely on its quantities you need to know what is in it, what is missing from it and how it is built. This check decides whether the quantities will hold up when the bill of quantities (BOQ) reaches the contractors.
What a construction quantity surveyor checks in the model before measuring
- Which disciplines exist. Architecture, structure, plumbing and building services, and how many files there are in each discipline.
- What was modelled and what was not. Sometimes the walls and floors are fully modelled, while the finishes, the waterproofing or the external works appear only on the drawings.
- How the elements were defined. A wall modelled as one layer or as several, a floor that does or does not include its covering. The definition changes the quantity.
- Floors and levels. Whether every element is assigned to the right floor, so that the quantities can be broken down by floor.
- Existing, demolished and new. In an existing building and in TAMA 38 projects (Israel's national plan for strengthening existing buildings against earthquakes, usually with added floors), I check whether the model distinguishes between what exists, what is demolished and what is built, because each of them goes into a different chapter of the BOQ.
- Revision and date. Which version each file was measured from, so that when a new version arrives it is clear what changed.
The number of files matters too. Working on one architectural file is one thing; opening five files in each discipline is a different scope of work. That is why I ask for the list of files and their names already at the quote stage.
Multiple files, twin buildings and typical floors
On large projects the model is made up of linked files. A twin tower, for example, is sometimes the same file linked twice. It is measured once and multiplied, not measured twice. But that identity has to be proven: a shared project ID is not proof that it is one model. The proof is when the same file is linked twice and both instances show the same elements.
Repetition is handled in two separate layers: identical buildings, and typical floors within a building. Each layer is shown on its own, together with what is left to calculate afresh, so every deduction can be checked. A whole project is not split in two just because two towers look alike, and basements or floors with a different area are not deducted.
Quantities with evidence for every element
The big advantage of working from a model is traceability. A quantity measured from the model rests on specific elements in it, and when a question comes up you can go back to the element itself instead of arguing about a number. The evidence is recorded for each building and each file, and a line without evidence stays empty; it does not get a zero.
This traceability is especially useful when a new version arrives. When the quantities are linked to elements, an element that was added, deleted or redefined shows up directly in the comparison, and the items it affects are marked. Instead of an argument about a total, there is a list of changes that can be checked one by one.
The model is part of the design material, and its correctness is the responsibility of the designers and consultants. My job is to know what I am relying on, to complete from the drawings and specifications whatever was not modelled, and to mark this in the BOQ. I worked this way, for example, on a residential building with piles and shoring and on a project where the quantities were taken from three models. The full list is on the projects page.
The model files for each discipline and their names, the area tables from the building permit, the current set of drawings in PDF and the specifications. There is no need to produce new material especially for the quote: send what exists, and note what has not been prepared yet.
When there is no model, or only DWG
Not every project has a model, and that is fine. If you need a construction quantity surveyor for a project designed only on drawings, you can still get a BOQ: the takeoff is done from DWG or PDF files, in the scope agreed in the quote, and this is stated in the document. The work is more manual, so it is important to receive area tables and current revisions right at the start. Sometimes only an IFC file arrives from other software. I can work from that too, as long as its limitations are known and it is checked against the drawings.
In every case the method is the same: a source for every quantity, written assumptions and marked gaps. You can read about the measurement itself, step by step, on the page about quantity takeoff for construction projects, and about the principles of the field on the page quantity surveying: the field, the methods and the tools.
What a professional quantity surveyor adds here. A good model still does not tell you what is missing from it. A quantity surveyor who comes from the field, an engineer or a registered building technician who worked on site, like Yaakov Avital, compares the model with the details and the specification. For example, the model defines one type of steel section while the detail shows another, or quantities that came out of the model do not match the PDF drawings. A professional check marks the gap as a question for the designer instead of passing it into the BOQ. More on the quantity cross-check page.
Even when the quantities come out of a Revit model, a quantity takeoff is checked against the drawings, because the model shows only what was drawn in it.
Frequently asked questions
Do you need a Revit model to work with me?
No. A model shortens part of the measurement and allows tracing by element, but a full BOQ can also be prepared from DWG or PDF drawings.
Our model is not finished yet. Can we start?
Yes. I measure what has been modelled, complete the rest from the drawings and mark which parts will be updated. When a new version arrives, I compare and mark what changed.
Are quantities from a model better than quantities from drawings?
They are more consistent and easier to trace, but they are only as good as the model itself. That is why the model check comes before the measurement, not after it.
What is the difference between a construction quantity surveyor and exporting tables from Revit?
Exporting tables gives you numbers. A quantity surveyor gives you a method: a check of the model, a structure of chapters and stages, item descriptions and units, and control of repetition and double counting. If you are looking for a quantity surveyor for construction projects who works from models, you are welcome to send the list of files. Contractors pricing a tender work this way too, as explained on the quantity surveyor for contractors page.
Have a project? Tell me briefly what the project is and what already exists. When the project is a good fit, I usually reply with focused questions and a written quote.
Contact me for a quote* Created with AI for marketing, for illustration only. Not reviewed by Yaakov Avital and not professional advice. Every project must be checked on its own by a professional quantity surveyor and an engineer.