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From a Revit or IFC Model to a Cost Estimate
How do I turn the quantities in a Revit or IFC model into a priced cost estimate?
Take an IFC model exported from Revit and turn its quantities into a cost estimate in OpenConstructionERP. We use a duplex model to inspect elements, extract quantities, apply unit rates and review what changes when the model is revised.
You will produce
Priced estimate lines built from the quantities of an IFC duplex model, with quantity rules that update when a new model version arrives.
Transcript
0:00 Why IFC
A 3D building model already knows how big every wall in it is. Today I'll turn that into a priced line in an estimate, for free, without a single plugin. This is for you if a designer sends you a model and you're the one who has to price it: estimators, small contractors, trade subs, owners checking a bid. Maybe you don't own the design software, so you end up measuring printed plans by hand anyway. By the end you'll open the model in a free app, pull a quantity out of it, and turn it into a priced line in your estimate. When the model changes, you'll update that line without starting over. All you need to start is the model saved as an IFC file. Four words first. BIM, building information modeling, means the design is a 3D model made of real parts, and each part carries data: what it is, which floor it's on, how big it is. IFC is an open file format for those models. A quantity takeoff, or QTO, is the count of what has to be built. And a bill of quantities, or BOQ, is the list of priced lines, each one a quantity times a unit rate. This app calls it the Bid Schedule. IFC isn't owned by any one software company. It's an international standard, ISO 16739, written so that different programs can share the same model, and it has a standard place for quantities. Revit has IFC export built in, under File, Export. That file is all you need. Sharing data is worth real money. A study for NIST, the US standards agency, put the cost of software that can't share data at $15.8 billion a year, across US building and industrial facilities, back in 2002. Owners and operators carried about two-thirds of it. Here's the model for the project: the Maple Street duplex, the same building we priced in the earlier videos. Two homes side by side under one roof, two storeys, 40 feet by 30, and it comes as an IFC file. Watch it come apart into the groups an estimator cares about: walls, floors, roof, doors, windows and stairs.
2:14 Model to quantity
In the app, open Takeoff in the sidebar and choose BIM 3D Takeoff. Drop the IFC file on the upload box and press Upload and Process. The box lists Revit files too, but I'm sticking to IFC, the open format. When it's done, the model opens in 3D, right in the browser. You can turn it, zoom in, and click any part. The app found 95 elements on 3 levels. A level is a floor of the building, named the way the designer named it. Open Filter and Group. By level, the parts sit on Level 1 and Level 2, and the roof has a level of its own. By category you get 24 walls, 20 windows, 12 doors, 4 slabs, 2 stairs and 1 roof. The 32 opening elements are the holes cut in the walls for the doors and windows. You don't buy a hole, so they never get a price. Click a wall, and its properties open: its type, its level, and further down, the quantities the file carries. Gross side area, 390. Net side area, 300. Those are square feet, straight from the file. The model is set up in feet, so there's nothing to convert. A wall can carry two areas. Gross is the whole face of the wall, 390 square feet here. Net is what's left after the window and door openings are cut out, 300. Siding is usually priced on the net area, so before you price anything, check which of the two your unit rate expects. To get that number for every outside wall at once, the app uses a quantity rule. A rule is a sentence: take every wall marked as exterior, read its net side area, add them up, and put the total on one line in the estimate. Write it once, and it runs again when the model changes. Open Quantity Rules under Takeoff and add a new rule. I name it Exterior walls, siding. The element type is IfcWall, the IFC name for a wall. I add a filter so only walls marked as exterior count, and for the quantity I pick the net side area from the file, in square feet. Then I test it: 8 walls match, 2,425 square feet in all. Save it, and the preview opens on its own. It's a dry run, so nothing is written yet: 8 elements matched, 1 rule, 1 new line. That's what I expect, so I press Apply. The estimate now has a line called Exterior walls, siding, tied to those 8 walls.
4:53 Quantity to price
The new line has a quantity but no price yet. It needs a unit rate, the price for one square foot. A good rate is built from resources: the material, the labor hours times the wage, and any equipment, added up for one unit. The Cost Database holds rates built that way. I search for siding. The closest match is metal siding on a metal frame with insulation, built from 10 resources, at $447.79 per 100 square feet. Per square foot, that's $4.48. It's a starting point, so set it to what you actually pay where you build. In the Bid Schedule, the new line sits at the bottom with its quantity already in, and a badge that says it came from the model. I type 4.48 as the rate, and the line comes to $10,864. Now the payoff. The architect moves the back wall out 2 feet, and a new file arrives. On the BIM page I add it as a new version of the same model. Open it, and the app offers to re-apply the rule. Nothing changes until you accept. The review shows the change: plus 107 square feet, worth $479.36 on this line. I accept, and the line now reads 2,532 square feet.
6:13 Checks and next steps
Plenty of firms already work this way. In a 2023 survey by RICS, the surveyors' professional body, about half of the respondents said they share data for takeoff and cost estimating through digital models. About one in five said they don't share it that way at all. A model only knows what the designer drew. Anything that wasn't modeled won't be counted, and anything modeled twice gets counted twice. A wall filed under the wrong category, or not marked as exterior, lands on the wrong line or on none. And if a rule test says skipped, no quantity, the file doesn't carry the number you asked for, so pick one the properties panel actually shows. Back in the estimate, the line from the model sits next to the rest of the job. Before it, the total was $191,869. Now it's $206,049, because the estimate adds overhead, profit and a safety margin called contingency on top of every line. One important note. Prices and quantities in cost databases and benchmarks are approximate, a guide only. Check every price and every quantity carefully yourself. We can't be responsible for errors. Before you trust a model takeoff, run four checks. Measure one element by hand and compare: the front wall on the first floor is 39 feet by 10, 390 square feet, just like the file says. Count the doors and windows against the schedules on the drawings. Choose net or gross on purpose. And list what the model leaves out, then price that by hand. You can do all of this with your own models, for free. OpenConstructionERP is free and open source, and the install video is right here. It walks you through setup, all the way to your first estimate.
