GRADING FOR ARCHITECTS
Do architects consider grading while designing the site? Yes, of course!
Do architects consider site drainage? Yes, of course!
Do architects concern themselves with cut and fill requirements to ensure minimal impact on the site and budget?
Do architects break out the calculator to ensure all the items above are met? Well, not so much… it is easier to estimate these items, and hand it off to the Civil Engineer.
What if Revit could automatically generate calculations for you? What if you could make informed decisions regarding finished floor elevations? What if cut and fill was analyzed automatically? Good news – Revit can perform these functions! Simply follow the steps as detailed below.
Property Line & Building Footprint
First, we will establish our plan layout with a property line and building footprint. The property line command is accessed through “Massing & Site > Modify Site > Property Line”. If you are creating this from a survey, you may create the boundary by entering distances and bearings. Alternatively, you may create the property line by sketching, which is the method explored in this example. We will assume a 300’ square property (approximately 2 acres); and a simple rectangular house, that is 5,000 square feet.
We will not create the actual building pad yet, rather define its extents with detail lines. If you have already drafted the building in Revit, then simply use the building outline itself, detail lines are not required. To keep the view clean, it is recommended to hide any categories that do not specifically pertain to the site plan.
Second, we will create the topography, which defines the surface of the site in three dimensions. The Toposurface command is accessed through “Massing & Site > Model Site > Toposurface”. For this example, we will draw the surface to directly align with the property. Some prefer to model the surface several feet beyond the property line, which is completely acceptable as well. The toposurface command will bring the user to sketch mode and ask for points. If you have a site plan or survey in DWG form (or other vector-based applications), you may quickly create the topography by referencing that file. For this example, we will select the four corners of the site, with an elevation value of 0’-0”. This will result in a 3-dimensional plane we may come back and edit it using “Modify I Topography > Edit Surface”.
Seeing as we do not have a DWG, we will fake in some contours to indicate a fall in elevation of 15 feet from one end of the site to the other. This is achieved with “Place Point” while indicating the “Elevation” in the Options Bar. You may notice some other lines automatically drawn while placing points. The toposurface will automatically interpolate the rest of the site while using any information that has been entered. In general, more points produce less interpolation. Fewer points will typically result in undesirable triangulation. Upon completion of all point modifications, the user will be left with a sloped surface with no thickness.
If you would like to see the variation in thickness underneath the surface, this may be achieved with “Section Box” from the Properties Bar. The default material for the section cut is Earth, however this may be revised to any material in the Settings. Note, the section box must be within the toposurface boundary. If the extents are outside the toposurface, the thickness will not be indicated.
Graded Region & Building Pad
Revit “Phases” may be assigned to Toposurfaces, just like any other element in the Revit environment. The existing site (before construction) shall have the Phase assignment “Phase Created – Existing” and “Phase Demolished – None”, which will inherit any Phase Filters as established in Phasing Settings. Site modifications will be documented using “Massing & Site > Modify Site > Graded Region”, which will indicate changes during the construction process. This command provides a couple options: “Create a new toposurface exactly like the existing one” or “Create a new toposurface based on perimeter points only”. The first option is more precise, while the second allows areas to be smoothed.
Either option will result in two toposurfaces. One existing, and one for new construction. The new surface will possess the Phase assignments “Phase Created – New Construction” and “Phase Demolished – None”. The original toposurface will be automatically be revised from its original assignment to “Phase Created – Existing” and “Phase Demolished – New Construction.”
Now a building pad may be modeled with the shape of your building footprint. This command is accessed in “Massing & Site > Model Site > Building Pad”, which will automatically initiate sketch mode. Verify your Phasing setting for the View is set to “Phase Filter – Show Complete” and “Phase – New Construction”. You will notice a void has been cut out of the toposurface in the shape of the building. In addition, a solid has been created for the actual building pad, with the thickness and material assigned in the Type Properties. The height of the building pad is specified in Instance Properties. Thus far, no contours have been modified with the exception a vertical cut or fill that falls directly in line with the building outline.
Modified Grading Around Building Pad
Next, we may address the grading around the building that responds to the flat slab on grade (or sloped grade if applicable). Edit the surface via “Modify I Topography > Edit Surface”. Draw a sweeping rectangle around the building and approximately 10 feet beyond. Delete these points, which defaults to contour interpolation based on other points outside the rectangle. Next, add points around the perimeter of the building as required by the wall sections. For example, if the detail shows grade 6” below finished floor, then add the points accordingly. The contours will automatically update to the new elevation points. If the automated contours are not desirable, add more elevation points which will provide more control of the grading.
Toggle between plan views and 3 dimensional views to ensure the result meets expectations. At this point, you may revise the Phasing to “Phase Filter – Show Complete” and override the Topography Category “Transparency” to 100. Your Site Plan will begin to look like a Grading Plan where new and undisturbed contours are solid lines, while modified contours are indicated as dashed lines.
Typically, it is best to equalize the cut and fill, so the contractor is neither hauling loads of soil off site, nor hauling loads to the site. A Revit schedule may automatically calculate the cut and fill in effort to produce a net zero result. A schedule may be produced via “View > Create > Schedule/Quantities” and selecting the “Topography” category. As always, the available fields are determined by the category. The fields “Cut” and “Fill” are available, however, you may also select “Net Cut/Fill”. The Revit schedule dialog has many other settings to assist with data population or visualization. For this purpose, we recommend the following:
Fields > Phase Created, Phase Demolished, Net Cut/Fill
Filter > None
Sorting/Grouping > Check “Grand Totals”, Select “Totals Only”
Formatting > Net Cut/Fill > Calculate Totals
Appearance > As Desired
Modify Finished Floor Elevation
At this point, we have a schedule that calculates the net value for all cut and fill of the entire site. If you have a positive number, then your current design would require dirt to be hauled off site. If your calculation indicates a negative number, then your design will require soil be brought to the property. Hence, if your schedule reflects a large positive or negative value, you may consider raising or lowering the building pad? Or perhaps altering another portion of the site? As the grading is modified, the schedule will continue to monitor the overall outcome.
Paving and Documentation
Now we have a property that shows grading to minimize cut and fill, based on the finished floor elevation of the building pad. But, what about paving or other site elements that need to be incorporated into the design? For these items, Revit utilizes “Massing & Site > Modify Site > Subregion”, which enables the user to define an area within the toposurface that will receive another material, like concrete, or brick pavers. Note, it does not create another element, it simply modifies the topography in place, which ensures the paving will follow the same contours.
As grading is finalized the user may begin to consider the best way to communicate this information in the Construction Documents. A Site Plan may be produced utilizing “Phase Filter – Show Complete” and “Phase – New Construction”. In addition, the Grading Plan is also available with “Phase Filter – Show All” and “Phase – New Construction”. Verify the Topography category is set to 100% Transparent, and the Building Pad is hidden in view. Finally, document the elevation of each contour with the tool “Massing & Site > Modify Site > Label Contours.”
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