Do-it-yourselfers can replace their roofing shingles fairly easily provided the home has straight eaves to measure from, but what if the roof is hipped?

In today’s economy, more and more able-bodied homeowners are doing their own repairs instead of hiring a contractor. If this includes replacing the old roof, this article may be of help.

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Common three-tab roofing shingles are simple to install. It’s just a matter of following a straight line and putting the nails in the right place. The instructions on each bundle show you how to nail them down properly, and how to chalk line the roof to keep them straight.

The lines that run horizontal to the edge of the roof are simple to mark. Just measure up from the edge twelve inches, minus however much overlap you want to hang off the bottom. For example, if you want a one-inch overlap, then the first line should be eleven inches up from the edge. Once you have that line, simply measure up every five inches from it for each additional run, all the way to the top of the roof.

The vertical lines that are needed to keep the tabs on the shingles straight are another matter. If the roof has straight eaves, you can just measure from them to set your two vertical lines six inches apart, but what about homes that have hipped roofs or tapered eaves?

Remember back in high school when we were all learning geometry and wondering, “When are we ever going to need this stuff?” Well, this is it. The Pythagorean Theorem, expressed as A squared plus B squared equals C squared, is a simple method of finding a perfect ninety-degree angle from the bottom edge of the roof.

I know, it sounds complicated, right? Lots of math to do to find all those square roots? Not really. I’ve simplified it here so that practically anyone can do this. It’s really as simple as 3-4-5. Remember those numbers and you’re already halfway there.

3-4-5 is the lowest whole number expression of the Pythagorean Theorem, in that three squared (9) plus four squared (16) equals five squared (25). The great thing about it is that it works for any multiple of those three numbers, whether it be 6-8-10 or 9-12-15 or however high you need to go, as long as you multiply each number equally.

What this means is that you can accurately and easily find a ninety-degree line by measuring from the lower edge of your roof only.

Let’s say that your roof is 22 feet high from edge to peak. Using the middle number of the equation, four, you divide wholly into 22 five times, so you’ll want to pop a horizontal line about five feet long at 20 feet up from the lower edge.

Now, knowing that your multiple is five, simply make a mark on the edge of the roof that you know is in the area below the five-foot-long horizontal line you just marked at 20 feet up, then measure along the edge of the roof 15 feet, which is five times the first number of the equation, three.

Using a long tape measure, hold the end exactly on the 15-foot mark, right at the very edge of the roof, and pull the other end up at an angle to the area where you marked the five-foot-long horizontal line. Using five once again as your multiple on the third number of the equation, that of 5, you know that the final line must be 25 feet long.

Keeping the tape measure pulled tight, simply mark the exact point where 25 feet on the tape measure intersects with the five-foot-long horizontal line you popped at 20 feet up from the edge.

This mark will now be perfectly straight above the beginning mark you made. Using your chalk line, pop this line from mark to mark, then measure over six inches from each end and pop another line. Now you have your starting point so that your shingles will be perfectly straight, with no guesswork involved.

The numbers used here, 15-20-25, fit into the Pythagorean Theorem perfectly. 15 squared (225) plus 20 squared (400) equals 25 squared (625). Hopefully, this simplification will make it easy for even a novice to install perfectly straight shingles. Good luck!