How to Calculate Materials for Roofing a House
Whether you are replacing your own roof or hiring a roofing company, you should get an estimate on the materials before beginning. If you choose a roofing company, it will provide a cost of materials, and you can compare that to your estimate to make sure you aren't paying extra.
- Draw a sketch of your roof area. Include any overhangs or dormers in this drawing.
- Measure the length of all lines and note them on your sketch. This can usually be done on the ground, but dormers and some overhangs may require you to be on the roof.
- Multiply the length by the width to get the area. Calculate dormers and overhangs separately and add them to the main roof area to get the total area for your roof.
- Select the shingles or other roofing material you want to use from a building supply store or home improvement store. Each material will have a certain amount of overlap, because shingles are installed overlapping each other to prevent water from seeping under the material.
- Divide the amount of overlap in inches by the length of the shingle in inches. This will give you the percent of overlap, or the extra materials you will need.
- Multiply the total area needed by the percent of overlap that you determined in step five. Add this number to the total area to get the total area of shingles you will need.
- Calculate the amount of tar paper needed using the total area of the room. You do not need to purchase extra tar paper for overlap like you do with shingles.