How Many Shingles Do You Need?

The biggest question most homeowners face when buying siding shingles is: how many do I need?

There’s a lot of terminology when it comes to buying sidewall shingles, and one that comes up constantly is the word “square.” But what does that mean, and how does it help you know how many boxes of shingles you need to cover your garage wall?

A “square” means the coverage of shingles needed for a 100 square foot area – that’s a 10 foot by 10 foot section of your project.

When you’re buying sidewall shingles, though, a “square” goes a lot longer, because you can use different exposures to get the coverage and look you desire.

“Exposure” means the length of shingle that will be exposed to the air – essentially, the amount of shingle you’ll see when the install is complete. When you’re doing roofing, exposure is tightly managed to make sure the roof won’t leak, but in siding jobs you have a lot more room to work with.

Most boxed shingles will have either a measurement chart showing how many square feet you can cover at the given exposure, or they’ll have a sentence describing “contains approximately X square feet at X inch exposure.”

So, how do we find this number for your project?

To get this calculation, you need to:

1.       Get your space measurement.

2.       Determine what exposure you want.

3.       Plan for your waste and any future repairs.

Step 1: Measure Your Space

The first step is measuring the space you want to shingle. Rectangular and square walls are pretty easy, but what if you have a triangular-shaped gable?

No matter what, you’ll need the length and width of the area you’d like to shingle. For squares and rectangles, just multiply the length by the width, and you’ll have your square footage number.

For a triangular-shaped gable, get the length and width, multiply them together and divide by two. You can also feed these numbers into Google’s Triangle Calculator.

To make things easier, you can also draw out a rough design of the walls you need to shingle, then put your measurements and square footage calculations on the ‘map’ to see how many square feet you need per surface.

Step 2: Determine The Exposure

Your second step is to decide what exposure you want for your shingles, if the shingle type allows it.

Fancy-cut shingles often need to be installed at a pre-set exposure, to get the pattern to look right. This exposure is usually around 7.5” and should also be listed on the side of the box.

With standard-cut boxed shingles and green shingles, there is a maximum and minimum exposure for every length of shingle. The maximum exposure of a standard-cut shingle is usually one half the actual shingle length. (For example: a 16-inch shingle’s maximum exposure is around 7 inches.) Shingles are often shorter than their advertised length, so an 18-inch shingle is usually more like 17 inches long.

You can use a larger exposure on your shingles if you run a second course or row of lower-grade shingles underneath. Double-coursing is when you install an additional lower-grade shingle behind the exterior higher-grade shingle. By doing this, you already have a layer of protective shingles below, so you don’t need the tight exposure on top to create your weatherproof layer.

If you’re doing double-course shingles, then you can get away with a much larger exposure – from about 2/3 to ¾ of the overall shingle length. (For example: 9 to 12 inches on a 15-inch shingle.)

Standard exposure for most shingles is 5-6 inches, and this is also the number most manufacturers use to get their “square” recommendations printed on the box. Use this as your guideline, but know that if you choose a larger exposure, you will get more coverage than the box advertises.

Step 3: Planning for Waste

The last step is calculating how much wastage you need to plan for, so you don’t get stuck with too few shingles.

There is always some natural variability in the quality of shingles in any given box, so you do need to plan for 3-5% waste. If you need a certain look or have a lot of triangular gables where you’ll have to cut shingles, then your wastage number could be even higher.

Step 4: Add it All Up

The final step is to take all these factors and calculate your needs, using the ‘square’ terminology as your guide.

·         Take your overall square footage number and divide that by 100.

·         Look at your desired shingle and find out its square ratio. (Ex. 4 boxes per square.)

·         Multiply your number of ‘squares’ by the number of boxes per square.

·         Add 5-10% on to that number.

And you have it! The number of boxes you need to order.

We hope this article will help you get the right number of shingles for your job, but if you have any questions don’t hesitate to reach out to us at: customerservice@CraftShingles.com.