Fun part of estimating is painting, but it is crucial to paint as you move on. This way you don’t leave anything out and you don’t count anything twice.

Now, we have to take off the slab, from inside the wall to inside the wall

Slab on grade = 32’ x 22’ x 4” = 32’x22’x0.33/27=8.6 cy   704 sf

Picture 2.9 Sample Foundation Plan, Complete Take Off

Let’s see what we have so far,

Column Footings                              7.11 cy 

Continuous Footings                       8.59 cy

            Walls     8’-0”                                      34.37 cy 

            4” Slab on grade 704 sf                  8.6 cy  

            Total Concrete                                  58.67 cy

Our estimate shows, we need 58.67 cy of concrete to be able to build this foundation.

When you are ordering the concrete, you can’t order 0.11 cy from concrete plant, you have to order 1/2cy increments.

So we need to round up our results to next ½ cy,

Column Footings                              7.50 cy 

Continuous Footings                       9.00 cy

            Walls     8’-0”                                      34.50 cy 

            4” Slab on grade 704 sf                  9.00 cy  

            Total Concrete                                  60.00 cy (1/2 CY round up result)

Now, let’s think more realistic. Assume you are the foremen at the site and you or your crew framed all the footings and you will be ordering for concrete. You calculated 7.25 cy for the column footings. if ground was 1” lower or if your frame work is ¼ “bigger than it supposed to, and some concrete will leak through between forms. 7.25 cy concrete may not be enough for you.

What happens if foremen order less than, what he needs:

--          He has to order missing order. What is the min. order he can order? A certain amount of cement paste always sticks to the walls of the inside of the concrete barrel. When you order 6 or 7 cubic yards, you lose little cement paste and it shouldn’t be big deal because of high volume. but if you only order ½ cy , cement paste will stick in the barrel will take away from the strength of the concrete because of low volume. Min order shouldn’t be less than 1 1/2 cy. So for missing ¼ cy, you may have to order 1 ½ cy. Now you have to much.

--          Usually, concrete plants are not next to job site, each delivery will take some time to get the job site. For that 1 1/2cy of concrete, ready mix plant will spend the same amount of fuel charges and driver time as 10 Cy concrete. That’s why there are short load charges.  The concrete plant will charge you for extra fuel and driver time plus for the concrete you ordered. Usually any order less than 6 cy, they charge short load fees.

--          While waiting for the next delivery, concrete may get dry and, you may get a cold joint on concrete pour. Inspector or owner or engineer may refuse the pour. You may have to replace that concrete element.At the end ordering little more than enough is always better than getting less. So we need to account for this in our estimate.We need to add ½ cy more for each event for each day. If event takes more than 1 day we need to add ½ cy for each day for that element,

At the end , ordering little more than enough is always better than getting less. So we need to account for this in our estimate.We need to add ½ cy more for each event for each day. If the event takes more than 1 day we need to add ½ cy for each day for that element,

Column Footings                              7.50 cy  +0.50 cy = 8.00 cy

Continuous Footings                       9.00 cy + 0.50 cy = 9.50 cy

            Walls     8’-0”                                      34.50 cy  +0.50 cy = 35.00 cy

            4” Slab on grade 704 sf                  9.00 cy   + 0.50 cy = 9.50 cy

            Total Concrete                                                                  = 62 cy ( ½ cy added result)

If we look in to rate of our end result to ½ cy round up result,

62  cy / 60 cy = 1.033 cy

3.3 percent more than our ½ cy round up result.

What we will do is ,

We will add 3.5 percent to our round up result total

60 cy (round up result) + (3.5 % = 2.1 cy = 2.5 cy ) = 62.5 cy

So at the end of our round up result we will add 3.5% waste that will cover all the missing days if event takes more than a day.

·         We always round up our calculations to next 1/2cy,

·         We will add some waste to end of our concrete take off. Depending on size of the job , this value varies from 2% to 5% . there are always wasted concrete, and we have to include in our estimate.

Concrete Quantities for our sample building as below

Column Footings                              7.50 cy 

Continuous Footings                       9.00 cy

Walls     8’-0”                                      34.50 cy 

4” Slab on grade 704 sf                  9.00 cy  

Total Concrete                                  60.00 cy

Waste 3.5%                                        2.50 cy

Grand Total                                        62.50 cy

This was the easy part.

How about reinforcing steel(rebar)?

How much rebar do we need to build this sample foundation?

Some contractors don’t calculate the weight of the rebar. They just assume each building gets average the same amount of rebar and they multiply concrete quantity with their market value cubic yard price. Some jobs they make money other jobs they may lose money.

Average size commercial building may take 150 lbs of rebar per cubic yard of concrete, but some jobs takes 300 lbs per cubic yard of concrete. 

We can’t gamble on this.

We have to estimate the rebar, so we can figure what is the realistic cost of the building.

Written by Kamil Cabuk , MS

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