Understand the process
Unless you are a cost estimator for a specialty trade contractor, chances are you will need to do cost estimating for cast-in-place concrete. Also, for those using unit pricing cost estimating for concrete works, here is a breakdown of how the cost is considered and calculated.
First things first. To properly determine the cost of concrete, we need to understand the process of concrete placement for any given project. No project is identical. The factors influencing the cast-in-place concrete cost are related to the type of project, weather conditions, geographical location, type of structural element, placing methodology, the size of each concrete pour, curing and finishing requirements, embedded items, access, type of form-work, type of hoisting required/available, skilled labour availability, etc. And among all, a cost estimator needs to be confident he/she understands how the concrete structure will be built. If you do not have the confidence that you understand the process of construction, reach out to someone who can guide you: a construction manager, site superintendent, crew foreman, etc. No question is a silly question. Make sure you ask them all to get the information you need.
Quantity take-offs
You might use an on-screen take-off software, or you do manual measurements of the printed drawings, the principle is the same: measure all elements that will be included in the cost.
Before attempting to do any measurements:
- review all the drawings for all disciplines. Most projects have structural, mechanical, electrical, and architectural interfaces. Concrete pipe supports, electrical equipment housekeeping pads, door concrete aprons, etc. These are examples of concrete elements found in other than structural drawings,
- review the project specifications, all sections on concrete, embedded metals, finishing, general conditions, schedule, etc.
- Remember that not all concrete standard specifications are included in the drawings. All standard requirements for concrete works must be followed and accounted for in the cost. Examples: placing and treatment of joints, finishing requirements, placing requirements (mass concrete, walls, slabs, etc.).
- understand the scope of work by others. Let’s take, for example, a flat surface finish. This activity might be done by the subcontractor. Communicate with the subs and clarify what they will include in their price and the exclusions. This way, when proceeding with the take-offs, you will be able to measure all quantities required by the subcontractor. You will be able to measure all activities not included in the subcontractor’s scope but required to be completed (take slab saw-cutting for contraction joints, for example).
Performing the quantity take-offs.
Regardless of whether the cost estimator performs the quantity take-offs themselves or if they are done by another party, I recommend that the requirements for take-off need to be established before this activity begins: items that need to be measured/counted, complete with item description, unit of measure, reference drawing(s) and it should include all activities: forming, placing, curing, finishing, concrete accessories. My definition of concrete accessories is all items/activities that are related to the concrete placing, like embedded metals, joint water-stop, concrete saw-cutting for control joints, foundation thermal/moisture protection (if not included elsewhere), etc. Do not forget the measurement of the block-out contact area for penetrations and openings.
Temporary works are an important element of cast-in-place concrete cost. Shoring and bracing need to be measured and included in the quantity take-offs.
The quantity take-off should be set up to include subtotals by type of structural element, type of concrete mix, and any other criteria that are considered relevant to pricing. Example: all flat concrete for elevated slabs, all flat concrete for stair landings, etc.
I always do the concrete take-offs in a sequence that is as close as it can be to the construction sequence. It is just my personal preference. Others like to do it by type of element. Either way is good, as long as the details are all captured and the scope of work is complete.
Performing the cost estimating.
Developing the cost estimate for cast-in-place concrete:
- develop the list of all construction activities required for the complete scope of work. It is assumed that at this stage, the estimator is already familiar with the construction methodology and the full scope of concrete works,
- think miscellaneous items and concrete accessories,
- think form-work prefabrication (if considered), on-site handling and cleaning, rental costs, etc.,
- think access for form-work installation and removal, reinforcing placement, concrete pour, cure and finish,
- review the list of activities with someone who will be involved in the cost estimate review process. This will be a good time to catch any missing activities and details required for a complete cost estimate,
- think about weather conditions and required concrete protection,
- set up crews for each activity,
- source material pricing for permanent materials,
- assign crew productivity to each activity,
- update resource costs: labour, materials (permanent and temporary), equipment, etc.
- update subcontractor pricing, including reinforcing.
- review cost estimate and add indirect costs: site supervision and support, temporary facilities and utilities, overhead and profit. If the concrete works are part of a larger cost estimate, the indirect costs would include only those related to the concrete scope.
This article was intended for the not-so-familiar with the concrete pricing cost estimator. In my opinion, the key to learning how to perform cast-in-place concrete cost estimating can be summarized into the following:
- thoroughly understand all activities related to a complete cast-in-place concrete scope of works. My suggestion is to talk with others with experience through the construction process and steps.
- crew composition and production rates. My proposed solution: research construction cost data. Read this article (including the comments) on LinkedIn for a list of resources available for the cost estimator. Some readers left comments that contained great information. I am not saying that the published data should be used as is. Crews and production rates can be modified as considered appropriate. Read this article on productivity for more details.
Do you have anything to add? Please leave your comments below.
