How To Measure Roof Squares

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Find this number by measuring the length and width of each plane on the roof (including dormers) then multiplying length times width. To find your roof’s total square footage, simply add the square footage of each of the planes together

If you’re intending on doing a shingle roof, you’re going to need to consider exactly how many shingles you will need to procure. To do this, you’ll need to assess the total square footage of your roof’s total surface. Doing so is straightforward. You or your hired roofing team will initiate by evaluating the span and width of each plane of the roof, adding to any dormers. Multiply the entire length by the width to receive the exact square footage of each plane. In the end, tally the roof’s full square footage by summing the square footage of each plane together.

Every roof surface is surveyed in “squares.” A square is purely any area of roof which computes at an exact 100 square feet. You’ll need to find out the number of squares on a roof in order to learn the number of shingles you’ll need to cover the roof. Let’s say you have a gable roof that is a sum of 24,000 square feet. Simply divide the entire square footage by 100. You’ll get a result of 240, meaning that you’ll need 240 squares of shingles to cover the roof.

How many bundles of shingles per square?

The most common type of shingle called a three-tab or strip shingle is generally packaged three bundles per square.

For a new roof, you will also need the same amount of underlayment. So, in the gable roof example above, you need 240 squares of underlayment. Underlayment usually comes in rolls of 4 squares each (240 ÷ 4 = 60). So you need 60 rolls of underlayment. No underlayment is needed if you are applying shingles directly over an existing asphalt roof.

Climbing around on a roof is not safe, so we do not recommend measuring the planes of your roof yourself. Plus, it is important that the measurement is accurate if it will be used to purchase roofing materials. So instead of going to the trouble yourself, contact a reliable roofer for an estimate. The roofer can use professional tools and methods to measure your roof and calculate the total square footage, and then provide estimates for shingles, underlayment, and other materials based on that total.

What About Other Roofing Costs?

Besides the shingles and underlayment, there are a few other things you should factor into your estimation:

  • Nails: Nails are sold by the pound. Assume that you’ll need about 2 ½ pounds of nails per square.
  • Flashing: This is a sheet metal barrier installed in all roof valleys and around any chimneys or vents to protect against water seepage. Unfortunately, there’s no simple way for a homeowner to estimate how much flashing you’ll need, so be sure to ask roofers to break this down when you’re getting estimates. 
  • Shingle Disposal: Your old shingles have to come off, so you’ll need a roofing dumpster to get rid of them. Your roofer will normally handle this, but you may be able to negotiate a bit of a discount if you offer to get the dumpster yourself.
  • Labor: Remember that you’re not just paying for materials. Be sure to ask the roofers you’re considering to separate labor and material costs in their estimates.

When measuring a roof some measurements need to be more accurate than others. For example, you could be a little off with the measurement of the ridge, hip, or valley and it wouldn’t make much of a difference in your expenses. However, if you don’t get accurate measurements of the width or length of the roof it could cost you more in materials than you estimated if you underestimate, or it could cost you the job if you overestimate and therefore bid an overbid price. If you were to measure a roof 100 feet by 120 feet that was actually 101 feet by 121 feet the difference would 221 sqft which is 2.21 squares of roofing materials which could be several hundred dollars.

Inspecting the Roof

Even if a homeowner is directing you to a specific area of the roof where they believe there is a leak, you should thoroughly inspect the whole roof. There may be more damage the homeowner does not know about, and you could save him/her money by catching it before it causes damage. Plus, this will help you sell a larger job and earn the homeowner’s trust.

When inspecting the roof, write down the following:

  • Any areas of damage.
  • The condition of the shingles.
  • The number, condition and length of eaves.
  • The number, condition and length of valleys.
  • The length and condition of hips and ridges.
  • The number and condition of vents, chimneys, plumbing vents and skylights.
  • The length and condition of all flashing.
  • Any unusual roof features, like solar panels and satellite dishes.
  • The number of layers of shingles and other materials already on the roof.

Before you climb down from the roof and return to speak to the homeowner, make a general plan of what the roof needs, so you can answer some of his/her questions up front. Leave the details to the bid.

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