1.8: Assemblies Cost Estimating

Learning Objectives

After reading this chapter, you should be able to:

• Describe the benefits and limitations of the assemblies estimating approach
• Develop an assemblies estimate for a building project
• Calculate the approximate cost differentials for selecting various system options for a project

Introduction

Once a project design progresses to a level where systems are defined, the team can continue with estimates that leverage the system information. If we refer back to our design phases, this level of estimates is primarily aligned with design development, when the systems are being designed, although some systems may be designed prior to this phase. These systems could include items as simple as the number of lavatories or toilets. It could also be more complex such as an assemblies estimate per square foot of building area for a mechanical system, such as rooftop units. It is important to note that some of the quantities used to develop the assemblies are straightforward, such as number of units for the lavatories, although others are more abstract, such as the square footage of the building for the mechanical system. An estimating team within a construction firm may have their own assemblies costs that they have historically tracked and categorized. This chapter will focus on using the Gordian guide for assemblies as a public source of cost information.

Assemblies estimates for commercial building projects are typically organized by CSI Uniformat 2 categories (see Figures 1 and 2) since they align with the overall building systems. This classification system is focused on building systems such as substructure (A), shell (B), interiors (C), services (D), equipment and furnishings (E), special construction and demolition (F), and building sitework (G) (see Figure 1 and 2 for the more detailed level 2 and 3 for each of these main – level 1 – categories).

Figure 1: Uniformat II – Categories A to F

Figure 2: Uniformat II – Element G for Building Sitework

To develop a full assemblies estimate for a project, an initial takeoff of the quantities for each type of building system is needed, along with an understanding of the type of building systems. The Gordian Assemblies Estimating Guide contains directions regarding the information provided for each assembly. Figures 3 and 4 contain the descriptions for the different information that is published for each of the assembly categories within the Gordian Assemblies Guide with RS Means data.

Each assembly is defined within the Gordian guide with a unique identifier along with a clear description of the detailed items within the assembly. For example, the stair construction assembly (A1010) shown in Figure 4 is developed by combining six more detailed items for a cast-in-place (C.I.P.) foundation wall. These six items are shown in the System Components section (noted with the number 5 in the image). These detailed items include formwork, reinforcing, reinforcing material handling, concrete, and finishing. It is important to note that you can read more details about what is included, and what is not included, in the description. For example, in Figure 4, we can see that excavation and backfill are not included in the foundation wall assembly. This assembly will be estimated with the unit of ‘cost per linear foot’ of the wall (see number 4 in Figure 4). It is important to note that you can not see the details for every assembly, but instead, you only see the details for one typical assembly per page. This one example is highlighted with its unique 12-character identifier (see number 1 in Figure 3 for example and the reference in number 2 in the same figure). For the remaining assemblies, you may need to assume the specific detailed items included, or you may have access to this information if you use the online version of the cost guides.

Figure 3: Description of Gordian Assemblies Guide information per Assembly (Source: Gordian Assemblies Estimating Guide)

Figure 4: Description of Gordian Assemblies Guide information per Assembly (cont.) (Source: Gordian Assemblies Estimating Guide)

Steps to Complete an Assemblies Estimate

Figure 5: Description of Steps to Complete an Assemblies Estimate (Source: Gordian Assemblies Estimating Guide)

Figure 6: Example of an Assembly in the Assemblies Estimate (Source: Gordian Assemblies Estimating Guide)

Figure 7: Summary of CSI MasterFormat Categories

Review Questions

 

References

Gordian. (2018). Assemblies Estimating Cost Guide.