- Understand to process to generate Quantity TakeOff from the model in order to generate the project budget.
- Understand how to use preliminary Cost Estimates to study different project design options by comparing conceptual masses estimates.
- Understand workflow to generate Quantity TakeOff from Model without using any other Software than Revit and Excel Office ©.
- Understand that Quantity TakeOff can be bi-directionally from model to external schedules and if necessary from them to the model with extra information.
- User has basic skills in BIM modelling with Revit Software, and understands the language used.
- User fully understands data structure in models (category > family > type > instance)
On this Guideline we will describe the workflow from Revit Material TakeOff and Quantity Schedule to .txt file exported that can be opened with a Microsoft Office© tool like Excel©.
We will explore how to use a model-based estimating workflow to provide useful cost feedback to the project team and inform decisions during all phases of design, from inception through construction.
First step in the project is to get conceptual estimates and compare the cost of proposed alternatives, and prepare preliminary estimates based on quantities of key building elements to confirm cost feasibility and evaluate proposed design changes.
1 Creating Quantity or Material TakeOff Schedules
When using a Revit model to generate Quantities you need to have developed a consistent model with enough construction elements definition. All through the modelling process you should be thinking about quantity TakeOff for budget so you take coherent decisions, Revit families and elements should be thought to be measurable and budgetable.
To generate all the quantities there are two differentiated options:
- Quantities Table: it can measure different categories elements and its parameters. Using quantities table is not a good a idea to select Multi-Category table because you will only be able to add common parameter to all Revit categories (which are very few).
- Material TakeOff: this option allows to measure all different materials included in a certain category or even all Revit categories by a Multi-Category table. You need to be careful using this kind of table and ensure materials are correctly applied to families and categories.
2 Schematic Design Cost estimates
During the early planning stages of a building project, you can analyze the conceptual design in several ways and for various purposes:
- The best mix of uses (such as retail, residential, and office space) for the building
- Rough cost estimates for the exterior of the building, based on linear dimensions or surface area.
Cost analysis is most beneficial in the early design stages of a project, when design decisions have the less impact on the project and they are easier to implement. For this reason, cost estimates based on the area or volume of a proposed conceptual design and comparison to historical data for facilities with similar functions and programming are especially valuable for confirming that the design is accurate and in accordance with the owner’s proposed project budget.
A easy way to generate a first approach to cost estimation is to create building spaces and add a new space parameter you can name Cost per Unit Area, and then a calculated value which will be the result of multiplying this new parameter (defined by established cost tables estimations) and the area of the spaces.
You can also do this operation using the spaces volume in which case the cost value will be more accurate.
In addition, to generate a quick building cost estimates you can use conceptual mass to create a simple model which allows us associate mass construction elements to a tabulate key quantities to generate first approach to budget.
You can use mass floors to divide a mass based on defined levels. For each mass floor, the software calculates the floor area, exterior surface area, volume, and perimeter. This information is stored in the instance properties for mass floors. You can include these values in schedules and tags.
- Select the mass and create Mass floors for every level in the model.
- After that, you can create a mass floor schedule to get a preliminary area of the building. Go to View > Create > Schedule/Quantities and make a new schedule for Mass floors
- To start, choose Level and Floor area from available fields. Add Grand Total and allow Floor area to calculate totals, in Formatting tab. Go back to fields selection and add a Calculated Value. Name it as Net area, choose Area as Type and create the Formula: Floor Area * 0.85.
- Add another Calculated Value. This time, you can name it as Ratio by Level and choose Percentage.
- After you have designed masses to explore a conceptual design for a building and you want to analyze the most cost-effective or profitable mix of uses for each floor of the building. So you need to assign usages to them as well. In this case you can calculate the percentage of floor space devoted to each usage and use this information to your benefit.
- Other great advantage of the software using both masses or any other method, is the conditional format to get visual results for checking.
Is not mandatory to start working with a 3D model to fit the program. We can start as we
were in AutoCAD but with the power of Revit. We can use Room separation lines under
Architecture > Room & Area to make closed polylines and make a room inside its bounds.Quite similar to the first option :Spaces.
Create a new Room schedule with the fields Name and Area. In a further step, you can draw walls on top of each line and begin to create geometry.
Once you have all rooms and it department, which could be useful to add, you can use color scheme tool to get a visual image and some useful data.
Design Options to compare results
You can create design options and use schedules to quickly compare the preliminary cost impacts as you vary the size, shape, and types of the model elements in each option.
- Create duplicate of the preliminary cost estimate schedules for each design option and use the visibility graphics overrides to display the appropriate data for each option.
- Place the preliminary cost estimate schedules for several options side-by-side on a sheet to easily compare the estimates for the different alternatives.
(See Key Schedules guideline)
Other tool that Revt offer us to help in cost estimation is the Key Schedule. It works exactly the same as if we add a Cost per unit area parameter in the type properties of each element. However, in this case you could have some key schedules stored in your Revit Template with the common finishes, materials or whatever from your common suppliers.
The problem with this workflow could be the human error. With the Type parameter option, once you have added it to a type, it will apply to every single instance from this type, so there isn’t any possible error. On contrast, using this tool, the person (that is not a machine) should apply the key schedule to the elements.
Of course you can group elements by type and apply the properties in one click, but each time you draw any new wall, you should do it again.
There are also other some tools that can make this repetitive tasks for us without any mistake like dynamo. If our project is huge, and the number of wall types is enormous, the task of filling cells is not very pleasant and repetitive, so we can use our computer to do it for us.
It is an example and it depends on the naming and coding standards to filter elements, but in essence could be like the following image.
Once you have the definition structure, you could apply to different model elements like floors, walls...and even use it for established construction ratios.
3 Detail Design Cost estimates
As the building design matures and construction details are accurately modeled, precise quantity takeoffs can be extracted from the BIM model to compute very detailed cost estimates that factor in the planned construction process and consider the labor, materials, equipment, and subcontractor costs for all building elements.
If we have started our model choosing the masses option, we can add now some model elements as floors by face, wall by face...to get a cost estimation at this step of the project, which is a little more accurate than the previous one.
Using construction elements
Once you have created the general building model, next step is to create either a Material TakeOff schedule or a Quantities Schedule. If you choose second option you will need to create one schedule for each category on the model: Wall schedule, Floor schedule, Curtain Panel schedule and Roof schedule.
In order to be able to calculate items cost you need to add cost parameter value either on the Type Properties Palette of the category or directly at the created schedule.
The basic Schedule you need to create an estimate cost will list parameter: Family and Type, Area, Cost and a calculated value you can named Cost Item and that will be the result of multiplying Cost by Area on each schedule category. You will get a schedule that looks like this:
This a quick way to generate an estimate cost of a project. Once you have all cost defined and schedules generated you need to export this table to a .txt file you will be able to open later with Excel.
4 Execution Model Cost estimates
As the level of detail for each element in the model increases, the level of costing detail can grow with it. So, as the design evolves and more details are specified, our cost estimates grow more and more precise.
Measuring structure steel weight
When measuring some kind of Revit categories we will need something more than areas, volumes or length. For steel structure usually you need weight, you can get this value either using steel density value or either
5 Exporting Schedules & Importing to Excel
Once you have learn how to generate appropriate schedule to export them: Revit > Export >Report > Schedule to create a .txt file you can then open with other softwares, on this case we are going to explain the process by using Office Excel.
Choose the destination folder and file name.
In this case, uncheck Export title and Export group headers, footers, and blank lines, and let the rest of the options as it is.
Open Excel. Go to Data tab and click on Get external data > From text . Select the file you have exported from Revit and check My data has headers.
In the next step, leave it as it is.
In the last step, click on Advanced and set the Decimal separator to “ . ” if you are not using an English version of Excel. Click on finish and choose where to put the data in your spreadsheet. You can let the default value to start in the first cell.
To better understand the values, we are going to make a Pivot table. Select any cell within the data imported. Go to Insert > Pivot table Click on OK with the default values. On the new palette in the right hand side of your window, drag Level and Department to Rows and Area to Values.
It is important to export all units without any symbol and itemize all elements if you are going to use Pivot Tables.
When you import a txt following those steps, there is a connection between both files, so if you update your revit and export it again, you will have the new values by refreshing (Data > Connections > Refresh all). Everything will update, both the RAW data and the Pivot table.
- When possible all modelled elements belong to a Revit category you should respect and not modelling all kind of things like generic model just because is quicker.
- Walls need to be modelled from one floor level to another, so you can break down it easily to create a correct measure approach.
- Finish layer when model is properly defined should be modelled as a separated but join independent element in order to have to most accurate measure possible.
- Connection between structural elements should be correctly modelled.
- Some detail elements are not worth it to be modelled and be defined only by detail drawings. You can get this elements measure by other elements parameter which define its number or quantity.
- If you have worked with Design Options to get the the draft which best fits with your area requirements or budgets estimations, you can duplicate the Schedule and change the Design option in V&G. It offers you to compare as much results as design options you have developed.
Some elements of a building project have a much greater impact on the total project cost than others. So, rather than estimating all elements with an equal level of detail and effort, it is better practice to identify the key building elements that drive total cost and focus design and estimating attention on them.
- Parameters Guideline
- Scheduling Guideline
- Masses Guideline
- Key Schedules guideline