This estimating guide is a continuation of our two-part series for contractors, on how to measure and estimate roofing prices. See part one of this guide to learn how to measure a roof.
Calculating Roofing Materials and Estimating Prices
For the purposes of this guide, I will use asphalt shingles as a default material, but the same principles can be applied to metal, slate, etc. Cedar shingles/shake will be slightly different, as the waste factor is higher.
Calculating roofing materials First – you need to know how many sq. ft. or squares of shingles you will need. You should take your total roof square footage and divide it by a 100 – this will give you the number of roof squares. Round the number up to the nearest square. Most shingle roofs will have 5-10% waste factor, and if you use most pieces during the installation, waste can be reduced to as little as 2-3%. If you have valleys / dormers and side-wall flashing, use 15% waste factor. See our roofing square guide, to learn how roofers and builders measure roofs.