Just How Flat is a Flat Roof?


While a flat roof may really seem flat when compared to a more conventional roof, it isn’t. Or, more accurately, it’s not quite flat. A flat roof can be more accurately referred to as a low-slope roof, but the exact definition of a flat roof is going to vary greatly depending on who you ask. In general, a roof with a tilt greater than 10 degrees is not considered flat. But often, you’ll see the steepness of a flat roof discussed as a ration (such as 1:80 or 1:40), so what does that mean?

What is 1:40? A ratio is a relationship. It describes how numbers group together. Think of it this way: if in 1 day you have 3 meals, then your day to meal ratio is 1:3. One day contains three meals. Here’s another example, the ratio for number-keys on most laptops (10) to letter-keys on most laptops (26) is 10:26, which can be simplified to 5:13. This means that for every 5 keys with a number, there are 13 keys with a letter. Of course, for flat roofs we use different units than days and meals or number- and letter-keys. Instead, the 1 is how many units of height are lost (how much down the roof has gone) and the second number is the number of units across. This means, a roof with a slope of 1:40 will lose 1 inch of height for every 40 inches of width. Or that it’ll lose 1 foot of height for every 40 feet. The units are irrelevant because the relationship stays the same regardless of whether you’re measuring in metres or miles. If your roof has a ratio of 1:40 and is 40 feet wide, it’ll lose only 1 foot of height from the highest section to lowest.

What does this Mean for You? The low slope is necessary in order to allow water to drain away, but it’s also minimal enough that you can easily enjoy your roof as a patio space, zen yoga retreat, and more! Many of our residential clients enjoy growing plants on their roofs, sunbathing, or reading. Others have put hot tubs, BBQs, or storage sheds on them. The uses for your flat roof are limited only by your imagination.

Flat roofs might not really be flat, but they’re definitely flat enough to easily and safely walk on and utilize. If you have a specific use in mind, it’s a good idea to speak with your flat roofing professional. We can guide you towards specific materials that will best meet your needs.

Considering a flat roof? Need to have your current flat roof repaired, inspected, or replaced? The experts at Vanderleek Roofing are here to help! Let us answer any of your questions and help you get back to enjoying your roof as soon as possible. Call us today!

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