FIGURE 11 Once we have established a scope of assessment and Tally’s project browser appears, we’re ready to start defining materials. Now it may seem at first glance that materials are already accounted for by virtue of this being a building information model. While this is partly true, we will see that in many cases we need to do a bit of work to translate from the abstract representation of materials found in a BIM model into the literal quantities of materials required for conducting life cycle assessment. In some cases we may also need to account for accessory materials like adhesives, coatings, and hardware, which are not typically modeled but should be accounted for.

If this were the first time we had used Tally on this project, all of items in the project browser would appear gray, which simply means that we have yet to build Tally definitions for those items. But since Tally saves all of the definitions we build back to the Revit model, it has retained a number of definitions from a previous session, which appear in green. Yellow items correspond to family types and categories with materials that remain undefined(). If we click on one of the green items, we will see details about the selected entry as well as the total weight of its constituent material. Below this total is a description of how Tally interprets the Revit takeoffs to determine that mass. In this case, we have modeled the ceiling layer to account for the true material thickness of insulation, so modeled volume is selected.

Defining MaterialsDetailed walkthrough of the Tally workflow.

TallyTM Tutorial: Defining Materials©2014 KT Innovations

FIGURE 12Later on, if we add, delete, or modify any instances of this family type, or even modify the thickness of the insulation layer, we could simply click the Refresh button or start a new session of Tally, and new totals would automatically be recalculated.

To see how definitions are built, I’ll edit the undefined entry for gypsum wallboard. This brings up a view of the Tally database. We can either navigate through Division 9 to find wallboard or use the textbox to quickly filter the entries.

FIGURE 14In many cases a membrane layer may be modeled with zero thickness, so using modeled volume would not be an option. Fortunately, Tally contains standard thicknesses and area densities for many sheet goods, including vapor barriers. In the event that such a layer has not been modeled at all, one can manually add it as an accessory layer.

Some materials, like metal studs, are modeled only implicitly by way of a void space, within which we know sections ought to be placed at regular intervals. Such items can be accounted for by defining the weight or area of the section and the spacing interval.

FIGURE 13Once we select standard gypsum wall board, we’re presented with a dialog that asks how Tally should calculate the total quantity and what finish it should apply. If we didn’t trust that the wallboard thickness was modeled accurately, we could use the modeled area method instead, and specify a thickness from a number of predefined options, or we could enter a manually-defined value. If we select a painted finish, then Tally knows to use the modeled area and simply asks for an application rate.

Each of the materials in the Tally database contains a default service life. This figure determines the number of times that material is replaced over the life of the building, so they have a significant influence on the environmental impacts incurred during the “maintenance and replacement” life cycle stage. For certain materials, such as structural steel and concrete, the default value is set to the building life. For other materials like gypsum and paint, we would expect them to be replaced periodically. The service life of a material is highly contingent upon its function in a building, so Tally allows us to adjust these figures independently for each family. If this were a wall surface in a dormitory or commercial interior, we might expect re-painting to occur on a more frequent cycle, but in the case of a ceiling we may set it to 15 years.

After we click save, the project browser item now appears green and displays the total mass of both drywall and paint that are required for the roughly 1700 square feet of this Ceiling type, along with the takeoff methods and service lives that we have selected.

FIGURE 15You will notice that when we save this definition, Tally automatically identifies all other instances of the same Revit material in the Ceilings category and asks whether we would like to apply them here as well. Since both ceiling types use a 2-1/2” stud section, we’ll go ahead and save ourselves the trouble of having to define this twice.

FIGURE 16Likewise after plywood sheathing has been defined in one ceiling type, we can copy that definition to other instances of plywood sheathing in other ceiling types.

FIGURE 17Some materials, such as aluminum mullions, may be modeled to account for their proper length, but may oversimplify the cross section. If we’re uncertain how one of these is modeled, we can make use of Tally’s visibility feature to temporarily isolate the mullion category or particular family type in the Revit view.

In this case the mullions have been modeled as solids, meaning a volumetric takeoff would drastically overestimate the quantity of aluminum required for construction. Tally provides several common mullion sections as well as many standard aluminum and steel sections to use in these circumstances. In this case, a reference table of perimeters can be used to determine the coverage area for various aluminum finishes.

FIGURE 18In the event that there is a Revit material with no environmental impacts, such as airspace, or a material whose impacts are covered by another entry, we can exclude it from our scope by assigning it as a dummy material. Unlike unassigned materials, dummy materials are treated as known entities, so a family type should turn green if each of its materials is either defined or a dummy.

FIGURE 19Once we have completely defined the materials in the model, the top level item should turn green. Since all of the definitions we have built up in this session are cached in the Revit model, we want make sure to save the Revit model to ensure that these definitions are retained.

At this point we’re ready to proceed with reporting.