How to Measure for a Metal Roof

A little planning goes a long way when it comes to measuring for a metal roof, so the first step is to create a rough sketch of your roof. Look at your roof from the ground and draw each slope, including the primary slopes and smaller slopes over doghouse dormers. Don’t worry about keeping your drawing to scale—your goal is just to make sure you don’t miss a slope once you’re on top of your home.

Label the slopes on your drawing, and then make a numbered list of all of the slopes below. Do the same thing for each of the ridges.

It’s time to get up on your roof, which is inherently dangerous, especially if your current roof is made of slick metal panels. It’s best to install a roofing harness before you start moving around on the slopes. Follow the manufacturer’s directions for installation, and check all connection points on the safety line before putting the harness on and connecting it. If you’re not comfortable getting up on the roof, hire a professional roofer to do it for you.

With your safety gear set up, it’s time to use your tape measure to start measuring your roof slopes. To keep things organized, start with the slope you labeled as “1” and continue through the list in order. Don’t worry about roof penetrations like chimneys and roof vents for now. Instead, record the length and width of just the slopes.

Before you get your feet back on solid ground, measure the ridges you numbered in order on your sketch. If you’re going to install gable-end flashing, measure each slope edge that ends at a gable, as well.

Next, look at your sketch and add 1 to 3 inches for metal roof overhang at the bottom of each slope. If you have a gable roof and don’t plan on installing gable-end flashing, add 1 to 3 inches to each gable-end measurement, as well.

Convert the measurements to feet and multiply the lengths and widths to get the square footage of each slope. Don’t add the numbers together. Unlike with an asphalt shingle roof, metal roofing panels are large, and you should install them with as few gaps as possible. Ordering based on total square footage will lead you to buy fewer panels than you need to minimize seams.

Use your measurements to figure out the materials you’ll need to cover all of the ridges and slopes. For the slopes, assume you won’t be cutting any of the panels, as using cut-offs will create unnecessary seams that increase the risk of leaking. Calculate the number of whole panels and pieces of ridge flashing and gable-end flashing you need for each part of your roof.

Most metal roofs have furring strips spaced at 2 feet apart across the length of each slope and along each slope edge. Use your sketch and measurements to make sure you order the proper number of 2-by-4 material for furring strips.