Roofing can be a challenging adventure to take on, but it doesn’t have to be scary. Whether you are measuring your roof to determine the amount of material you will need for replacement or whether you simply need to consider whether the roof’s pitch is sufficient for proper drainage of rain and snow, you may need to know how to measure the pitch of your roof.
In layman’s terms, a roof pitch tells you exactly how slanted or steep your roof is. To be more precise, think back you your high school Algebra days. (I know, I know. Bad memories of a harried teacher who smells of cigarette smoke and mothballs come to mind.) Bear with me for a moment as we conjure up what it took to pass the class. At some point, you probably were taught a concept called slope. Slope, a constant change over time, rise over run…is it all coming back to you now? No? Ah, well. Mrs. Crumple must be turning over in her grave.
Nevertheless, slope (or a roof pitch) tells us that for every so many units we travel forward, we will travel up another set number of units. This is where the concept of rise over run comes in. When we refer to a roof as having a 4/12 pitch, what that really means is that for every 12 inches you travel horizontally on your roof, you would travel 4 inches vertically. Sounds simple enough, doesn’t it?
So, with that in mind, let’s consider other fractions or roof pitches. If you take a look at a roof that is a 2/12 pitch, that means the roof only rises 2 inches for every 12 inches you proceeded horizontally. Picture that, if you would, in your mind. If you were to walk 12 feet forward and be 2 feet higher than when you started, that would be less steep and require less climbing work than if you were to walk 12 feet and be 6 feet higher than when you started. Subsequently, if you were to walk 12 feet forward and end up 10 feet higher than when you started, that would have been quite a strenuous climb!
Now that you have it pictured in your mind what slope and roof pitch looks like, you can see that the higher the numerator (the top number) gets while the bottom number or denominator stays the same, the steeper or harder to climb the roof will be. Picture, if you will, an A-frame home. Because of the extreme nature of the building, the roof pitch on an A-frame might well be 16/12 or greater.
If you want a hands-on experience when measuring the pitch of your roof, you can measure in a couple of different ways. For the first method, gather the following: a tape measure, a level (preferably a two-foot level), and a carpenter’s pencil. Find a ladder that is sufficient to safely reach the fly rafters on either side of your gabled roof. If you need to stand higher than the next to the last step on a folding ladder, use an extension ladder for safety’s sake.
Once you are on viewing level with your gable, place the level on the gable side of your house. Slide it to the left or right until the upper left or upper right corner of the level touches where the shingles overhang the gable. Adjust your level, making sure the level bubble is sufficiently centered and, while holding the level in place, make a mark at the end of your level. If you have a two-foot level, this mark will fall exactly at two feet. If you have a level longer than two feet, you may want to mark at either one or two feet and then transfer that mark to your gable. Once you have that mark, you know it is exactly two feet horizontally from the underside of the shingles where you started at the lower end of your roof. Pull out your tape measure and measure vertically from your mark to the underside of the overhanging shingles directly above. Take note of that measurement. Create your fraction. For example, you might have measured 2 feet horizontally with your level and then 6 inches vertically from that point. Convert your feet into inches so you now have that you traveled 6 inches vertically after having traveled 24 inches horizontally. Reduce your fraction: 6/24 = 3/12. You have just determined that for every 12 inches you travel horizontally, you travel 3 inches vertically.
If you don’t have gables or you have different sections of roof that are different pitches, you can also measure while physically on the roof. You will need, in addition to the tape measure and level, some wooden blocks of various sizes to help brace the level. Use the ladder to climb onto the section of the roof you plan to measure. Place one end of your level at the higher portion of your roof and hold it straight out horizontally, adjusting the level so it sits level with the bubble within the level lines. Use your wooden blocks to build up support at the lower end so that you can set the side of the level you are holding on them.
Once you have the blocks holding the level perfectly level with one end on the high side of the roof and one end supported on your wooden block supports, you are ready to measure. Pull out your measuring tape and measure from the end of your level that is supported on the blocks straight down till you hit the roof below. Notice, this time you have come straight out horizontally from your roof by 2 feet (if you are using that two-foot level), and then you dropped with your tape measure vertically by however many inches you measured.
Let’s say you measured down from the end of your two-foot level and found the roof was 4 inches down. This tells you that when you traveled 2 feet (or 24 inches) horizontally, you then dropped 4 inches vertically, for a roof pitch of 4/24 or (reduced) 2/12. So, this roof would be a 2/12 roof pitch, meaning that for every 12 inches you traveled horizontally, the roof is rising by 2 inches.
But, what’s that? You aren’t that much of a hands-on gal or guy? You’d rather have an easier way of measuring than climbing up rickety old ladders and clinging precariously to your roof gables? You’re in luck. You can now contract with companies who will take or use satellite roof measurements of your roof and provide you with accurate roof pitch measurements. These satellite measurements work more accurately because they can take pictures from various sides, and give a detailed three-dimensional representation of your roof; handy for those more complicated roofing systems that have multiple pitches.
Often, satellite photos already exist due to auditor and property information or online mapping software. Satellite roof measuring services, therefore, generally are low-cost and can produce accurate and up-to-date information not only on the pitch of your roof, but the area, ridges, valleys, and hips and their respective lengths. Satellite roof measuring can be an economical way to gain multiple pieces of information on your existing roof that may be helpful in upcoming, as well as current roofing projects.