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Under One Roof

Canadian Roofing Reference Manual

4.1.6 Material Quantities

Should you become a superintendent, estimator, or roofing contractor, it will be necessary for you to determine material quantities. It is important that you thoroughly understand the application procedures of the material, drawings, specifications, and mathematical calculations using ratios and proportions. Always double check calculations. Improper calculations can lead to shortages or surpluses of materials, which directly leads to over or underbidding of a project.

There are basically two major steps in the procedure for determining the material quantities needed to complete a project. These are:

  1. Identify the materials required.
  2. Calculate the quantity of materials required.

Identify the Materials Required

There are basically two steps in the procedure for identifying the materials required. These are:

  1. List the materials required.
  2. List the coverage required.

If you follow each of these steps in order you should be able to successfully identify the materials required for a project.

  1. List the Materials Required
    To complete any roof, you must first identify and list every type of material required. The building blueprints, specifications, or the CRCA Specification manual are used to complete an itemized list of materials. In some cases, the building specification will provide you with a material list, outlining the standard(s) the material must conform to. (e.g. CSA or CGSB numbers and manufacturer). You must carefully read through the specifications, while visualizing the installation, make note of, every type of material you will need.
  2. List the Coverage Required Once the materials list is complete, you must then identify the packaged unit Material coverages are obtained from the manufacturer’s data sheets. Make note of the material coverage rates. Always double check to ensure that no required material has been left off your list.

Calculate the Quantity of Materials Required

Once you have identified the materials required for a project, you must then calculate the number of each unit required to complete the roof area and perimeter of the building. Round up the results to full units.

Once you have determined the type of materials and calculated the quantity of materials you will need, you will have to add an allowance for scrap and waste. This allowance will depend on the complexity of the roof (i.e. number of elevations, shape, number of units and penetrations etc.). Cut-up roofs that are irregularly shaped will have more scrap than simple box like roofs. Also, some material is bound to be damaged during transit or installation. It is always better to have slightly more than required than to have a crew standing around because you didn’t bring enough materials to the job site. However, bringing too much will mean that you will have to take what is left off the job and reload it onto the truck. For this reason, always recheck your calculations.