The purpose of this article is to provide a brief overview of how to calculate a job cost using insulating concrete forms (ICFs). Always refer to the ICF manufacturer manuals for specific methods.
To job cost a project using ICFs, you need only a few pieces of information: the external linear length of wall, the external height of the wall, the number of 90 degree corners, and the number of 45 degree corners. This information can be found on the project plans. For this example, 114 meters will be used as the linear length of wall.
Count the number of 90 degree corners in the building. Multiply the number of 90 degree corners by the length of one 90 degree corner. For this example, use 1.2 meters for each 90 degree corner. If the project had thirteen (13) 90 degree corners, then the total length in 90 degree corner forms would be 13 times 1.2 meters or 15.6 meters. Follow the same method for the 45 degree corners using 0.94 meters for the length of each 45 degree corner. In this example, the project has four (4) 45 degree corners which would equal 3.76 meters. Add these two values together to get the total lineal length of corner forms. In this example, the project has 19.36 meters of corner length.
Subtract the total lineal length of corners from the total lineal length of the walls. 114 meters of wall minus 19.36 meters of corner equals 94.64 meters. Divide this number by the length of a straight form. For our example, the length of a straight form is 2.438 meters. 94.64 meters divided by 2.438 equals 38.8. This is the number of straight forms per course.
To get the number of courses for the wall, divide the wall height by the height of one form. For our example, the height of one form is 0.457 meters. Round up to the nearest form. Assuming a 3.658 meter wall height, this project would need 8 courses.
The number of straight forms equals the number of straight forms per course multiplied by the number of courses. The number of 90 degree corner forms needed equal the number of 90 degree corners in the building times the number of courses. The number of 45 degree corners needed equals the number of 45 degree corners in the building times the number of courses. This project would need 311 straight forms, one hundred and four (104) 90 degree corners, and thirty-two (32) 45 degree corners.
It is possible to reduce the number of straight forms needed by calculating the total area of straight forms and subtracting the total area of all windows and doors. For this calculation, use 1.12 square meters per straight form. However, care should be taken to account for construction error and wastes. Also consider that T corner forms would be used in the place of straight forms in intersecting corners.
The amount of concrete need is calculated by totaling the cavity volume of each form used. Each straight form holds 0.12 cubic meters of concrete. The 90 degree and 45 degree corners hold 0.048 cubic meters and 0.046 cubic meters respectively. Considering that horizontal rebar is placed in every course and vertical rebar is placed every 40 cm, this project would need 1,028.7 meters of rebar.
Labor is calculated using 0.424 hours per form. This includes the time it would take a two person crew to build the ICF building, place rebar, and pour concrete. In this project, 447 forms would be used. It would take a two person crew 190 hours or 5 weeks to complete this project.
Light Ready Construction
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