There’s nothing worse than being smack dab in the middle of a home improvement project and running out of supplies. You have to stop what you’re doing and head back to the hardware store covered in dirt, wasting more time when you just want to be done and crack a beer. Problems like this can ruin the joy of building something yourself. So, to prevent this problem we’re going to go through how to estimate the amount of shingles you need for your roofing job.
You can buy roof shingles by the bundle or by the square. A square is the number of shingles needed to cover 100 square feet of roof. Heavier shingles require more bundles per square. Usually three bundles to a square is the most common.
Figuring Out Roof Area
First you need to figure out the size of the roof area to determine the amount of bundles you need. You can do this by measuring, which is the most accurate way to determine the amount of shingles needed. To do this, you’ll get on the roof and measure each roof plane. If your roof planes are rectangles you just need to multiply the length times the width of each plane to get the square footage and then add up the square footage of each plane.
Roof Plane Length x Roof Plane Width = Square Foot
The number that you get above isn’t going to be enough. You need shingles for starter courses along the eaves, rakes, hips and ridges. If you have a simple roof figure 1% as the waste factor. If you have a roof with lots of open valleys add 5%. Unfortunately, there’s not a single calculation you can use to determine the shingles needed for waste. You’ll have to feel it out. This is especially true because it’s inevitable that some shingles will be damaged by dropping them and improper nailing. One extra bundle is sometimes enough, but if you’re new to roofing, mistakes are sure to be made so a couple extra bundles is playing it safe.
On woven valleys, each course of shingles extends beyond the crease and at least 12 inches on the adjacent roof plane. You’ll need 2 feet of extra shingle material for each pair of woven courses. Cut valleys extend 12 inches as well. Order two extra shingles per linear foot of cut valley. On a 16 foot valley you need 32 shingles or about one extra bundle. If you feel overwhelmed by all of this, it’s natural. Redoing your roof is a big task. Just remember to plan for a lot of waste if you’re new to roofing and you should do just fine.