Accuracy is everything in estimating. And making a comprehensive and complete take off list is the first and most important step.
Throughout this article I will use the example of a roofing takeoff to demonstrate the steps and show the final example of what a takeoff list should look like.
Measure the Basics
There are four basic measurements that go into doing a takeoff. Count, Linear / length, Area and Volume. For any construction item, you have to decide what is the best and most appropriate way to measure them. Easy, right…
If you want to measure the number of light fixtures in a room, then counting them would obviously be the best way of doing that. If you want to measure the wall base used in a room then length would probably be the best way.
For our roofing example lets start by measuring the flat area of the roof on the roof plan. And also measure the flat lengths of the hips, ridges, gables and valleys, again from the roof plan. Please note that in this case we would need to measure the area / length for each item separately for different roof pitches / angles.
Convert Basic Measurements to Material Quantities
The four types of raw measurements I described above need to be converted to actual estimate of material quantities required. There are two steps to this.
Step 1: Convert raw measurements to gross measurements
This step may or may not be required depending on the item and the measurement. For example, the count of light fixtures in a room doesn’t need any conversion. However, the length of a wall will need to be converted to the surface area of the wall (by multiplying height) as the first step to calculate the paint required for its finishing.
In our roofing example, we need to convert the flat area measurement of the roof by using the slope and a trigonometric formula to calculate the actual gross area or the sloped area of the roof. Similarly the flat length of the hips need to be converted to the actual gross length of the hips. Same for the other measurements.
Step 2: Convert gross measurements to Material quantities
The second step is to convert the gross measurements to material quantities. This depends on how the material is sold / purchased. This step is usually required for most items. For example, paint comes in buckets of various sizes in liters. So first you would need to convert wall area into amount of paint in liters that you would need. This is done by Dividing total wall area in SF by the amount of paint in liters required per SF.
Lets continue with our roofing takeoff. Lets assume the roofing material used are roof shingles. We would need to first calculate the area covered by 1 roof shingle. This depends on the exact brand and product being used. We would then divide the total roof area by area of 1 shingle to get the number of shingles required. So we have converted roof area measurement into the quantity or count of shingles required. As we will see later in this example, more steps are needed to refine this further.
Add Wastage
Extremely important to add the right amount of waste. I won’t get into too much detail on why there is waste and how to accurately estimate waste. Instead use the following rule of thumb. The bigger the size of the item, the more the waste. And the bigger the size of the installation area the lower the waste.
For example if you use small tiles of 4”x4” to install in a room the waste will be much lower vs. if you use tiles of 24”x24” size in the same room. Also, if you use 24”x24” tiles in a small room, the waste will be much more compared to using them in a very large room like a hall.
In our roofing example, using large sized shingles will lead to more waste while smaller sized shingles lead to less material waste. Adding waste to gross quantities converts them into net quantities.
Convert Net quantities to generate a Bill of materials
Again, there are two steps to this. The first step is to convert net quantities to actual purchase quantities. The next step is to add supporting or installation materials.
Step 1: Adjust for the real world
Unfortunately, your material supplier doesn’t supply a pack of 33.4 shingles. Guess what! There are exactly 32 shingles in a pack for the one you want. Which basically means that real life sucks. So now you have to buy 64 shingles or a pack of 2 shingles for a roof that needs 33.4 shingles. Rinse and repeat for all the items in your list.
Step 2: Add items needed for the journey
Any roof installer knows that shingles aren’t going to glue themselves to the roof automatically. Same goes for almost any item that you can think of. You may require a primer before you start painting for example.So go through all the additional or installation items you need and add them to the list. Thankfully you already have the gross measurements you need.
But you will need to go through the whole process of going from gross measurements to converting them to actual purchase quantities for each of the items you add as described above.
Congratulations! You Finally have a Comprehensive Take off List!