BIM model enrichment: how much it helps, and what goes into the model to run a BOQ on it
BIM model enrichment is the work that turns a Revit model built for drawings into a model you can run a bill of quantities (BOQ) on. Every element gets a consistent type, a chapter and item assignment, a material, a floor and a room, and only then does the quantity come out of the model and get checked against the drawings. I have experience in taking off quantities from Revit models and in preparing them for a BOQ, in architects' models and in engineers' models.
What BIM gives a quantity surveyor, and what it does not
In a BIM model every element carries data: type, dimensions, material, floor and sometimes a room. For a quantity surveyor this means that quantities that take hours to measure on drawings come out of the model quickly, and that all the designers work from the same source. In coordination between the disciplines, for example in Navisworks, clashes are found, such as an air-conditioning duct running through a beam, before they become a variation on site. When every element is linked to an activity in the construction programme you get a fourth dimension, and when it is linked to a price you get a fifth dimension, cost. Information management itself has an international series of standards, ISO 19650, which defines roles, stages and methods of delivery.
What BIM does not give on its own: methods of measurement, waste, and works that were not modelled as elements, such as waterproofing, fill or ancillary works. A model built for drawings often holds one wall for two floors, one slab for all its layers, or a generic type called "Wall 20" with no material. Hence the need for enrichment.
| Data | In a model built for drawings | After model enrichment |
|---|---|---|
| Element type | Sometimes generic, like "Wall 20" | A consistent type with material and layers |
| Chapter and item | Usually none | A chapter and item code on every element |
| Floor | Sometimes one element for two floors | A separate element for each floor |
| Room | Spaces without a room, or not enclosed | Every space with a room, a name and a number |
| Unit of measurement | Not defined | m², m³, m or each, according to the item |
| Duplicates | Overlapping elements | Deleted, or flagged for checking |
BIM model enrichment in practice: six actions
- Merging types: the same block wall sometimes appears under three names. They are merged into one type with a material and a thickness, so that all of its quantity goes into the same line.
- Classification by specification chapter: every element gets a parameter with a chapter and an item. In the General Specification for building works (Israel's inter-ministerial specification), for example, chapter 02 is cast-in-situ concrete, chapter 04 is masonry, chapter 09 is plaster and chapter 10 is flooring and wall tiling.
- Materials and layers: an external wall is built of layers of internal plaster, block, insulation and cladding. When the layers are defined, each one is measured separately.
- Floors and rooms: elements are split by floor, and rooms are closed with a name and a number. Flooring, plaster and paint all rely on the rooms.
- Parameters for the bill: an item code, a unit of measurement and a location, such as building, floor and flat, so that the bill can be split by construction stages.
- Clean-up: duplicates are deleted and the joins between walls, slabs and columns are fixed, so that the junctions are not counted twice.
The add-in I developed for Revit has a button for most of these actions: "Create rooms", "Update room names", "Assign flats", "Link items to elements", "Finishes and waterproofing completions", "Live BOQ" and "Select unlinked", which selects in the model the elements that no rule has caught. The flow in short: model for drawings → model enrichment → running the BOQ on the model → check against the drawings → final bill. How to calculate from there, element by element, is explained on the model quantity takeoff page.
Example: a typical floor before and after BIM model enrichment
The numbers are for illustration only, but their kind is familiar from every model that comes from drafting:
| Check | Before | After |
|---|---|---|
| Elements on the floor | 1,240 | 1,212 |
| Elements without an item code | 410 | 0 |
| Overlapping duplicates | 28 | 0 |
| Walls that run through two floors | 36 | 0 |
| Spaces without an enclosed room | 9 | 0 |
410 out of 1,240 is about a third of the elements: a third of the floor that would not have gone into any item. The 28 duplicates are the difference between 1,240 and 1,212. If these are block walls 2.8 m high with an average length of 4 m, that is about 314 m² of blockwork that would have been counted twice: 28 times 4 times 2.8. In a rendering this error is invisible. In the price it is very visible.
Readiness check before running a BOQ on the model
Before running it, I go through a short list. A model that fails it is not thrown away: whatever is missing is recorded as missing, not as zero, and checked by hand.
| Check | How to check | Passes when |
|---|---|---|
| Item code | A filtered list of elements without a code | No element without a code |
| Duplicates | A check for overlapping elements in the same location | No overlaps |
| Floors | Every element is assigned to one floor | No element on two floors |
| Rooms | Every space is enclosed, with a name and a number | No space without a room |
| Units | One unit for each item | No total that adds up different units |
| Match with the drawings | Floor area and wall lengths against the plan | Every difference is explained |
The last line is worth doing every time, even with an excellent model. How to cross-check numbers between sources is explained on the quantity cross-check page. If you work from 2D drawings, you can link them to the model as well, as described on the AutoCAD quantity takeoff page.
The rule: a model without enrichment gives a number. A model after enrichment gives a number you can explain: which element it comes from, in which unit, and under which item.
An enriched model shortens the quantity takeoff, but it does not replace the check against the drawings and the specification.
Frequently asked questions
Is every Revit model suitable for a BOQ?
Not without preparation. A model built for drawings suits drawings; to suit quantities it needs enrichment, and sometimes also the addition of elements that were not modelled, such as finish layers or waterproofing.
What is the difference between BIM model enrichment and MEP coordination?
MEP coordination looks for clashes between the disciplines. Model enrichment adds to the elements the data that the BOQ needs. Both are done on the same model, and in a well-run project in the same round.
Can you work from an IFC file?
Yes. An IFC file carries elements and properties, and the properties have to be mapped to chapters and items. More on extracting quantities from Revit is on the quantities from a Revit model page.
Who does the enrichment?
The modeller or the BIM coordinator, together with a quantity surveyor for construction projects who knows what the bill needs. That way the enrichment is done once, according to the items.
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.