Roof pitch formula

Good morning everyone. I hope you all are having a good day!! I have a question have any of you used the Roof formula measuring from the ground. Ex: outside measuring 30x33 x 1.73 ( 12x12 ) then multiplied by 17% for cut up hip with valleys? I can't get up to measure usually if I can I do. Eagle view can't get good measurements too many trees. Any help would be greatly appreciated. Thanks in advance. :)

For years, I measured plans with the 3-sided ruler technique. Then, after one I underbid, I started using a quick pitch factor measurement to verify my measurements.

I recently had to explain to my grandson what the engineers scale in my desk drawer was for and realized I hadn't used it in his lifetime (he's 10). All plans I have gotten on the computer, I have used the pitch factor method.

About 30 years ago, we did a big apartment job and it was 12/12 three and four stories and all cut up. That is when we pulled the trigger and bought a LOT of pipe scaffold. Best investment we ever made. It doesn't wear out and it makes it safer and faster to do the cut up steep jobs. When you get used to it, it doesn't take all that long to set up and you don't need all the ropes and harnesses either. the debris doesn't hit the ground, you have a place for the tools and materials and the ground stays clean too. OSHA will leave you alone too. I highly recommend it.

I've always been a fan of get out the ladder and tape measure and get close and personal on something you may be married to for the next five years or more. Climbed a few steep ones and sat up on the ridge and contemplated whether I should give them a bid or walk away. You get a different perspective sitting up there on a 12/12 with no ground in sight and all you see are the walls of the neighbors houses in the strike zone of any sliding debris. Steep pitch roofing is a specialized process, more so when re-roofing, and consider yourself lucky if you make a decent profit on the first one you bid. You may want to stick with the 1.73 number and use the returns as your wage if you are paying a crew by the hour to do the install. With the OSHA rules today l can't imagine the cost to be compliant on some of the roofs I did years ago. We used to have a full truckload of gear to haul in to do a steep slope. Scaffolding, dozens of roof brackets, 2"x10" walk planks on the bottom as a main walk to the ladder hoist, step ladders and on and on. Looked like a game of snakes and ladders. 200-300 man hours expended on some of these old slugs. Thankful the labor rate was only 5-6 bucks an hour back then. These young pups today probably wouldn't be able to do it.

thanks guys.hey egg,your right about the 1.73 i was mistaken i should've used the 1.41. the 17% waste factor was because its a hip roof ( forgot to mention that) with dormers on each hip. those hips also have those small little returns that go back into the wall. as we all try to do i tell the men to use all there pieces because its a hip. there pretty good about this. seriously, Thanks for all the help!! have a great day be safe!

Thanks Egg. The guys on this forum are brilliant! It is a privilege to be able to contribute. Your story on the waste factor reminded me of the contractor we used to work for. They would have a new house ready and they would add some squares to the total when they told us how big it was. We would then add to that to make sure we had enough when we brought out shingles some times, you would end up with 10 extra aquares on the truck. Nothing lost mind you, but when you drove up to a house with 40 squares on the truck for a 30 square house it was funny!

If we need a tight calculation for pitch factors, taking the example given of 12/12, I don't see how we get 1.73

This is how the math goes: A squared plus B squared = C squared. A (the rise...12...squared (meaning times itself) is twelve times twelve or 144.

B (the run...level) times itself is also equal to 144 (12 times 12)

A squared plus B squared then equals 144 plus 144, or 288.

288, then, is C squared (C is the length of the rafter you're trying to find out) It turns out that 17 times 17 is extremely close to 288. So the rafter is 17.

So how much bigger is 17 than the 12 you measure from the ground? When i divide 17 by 12 I get approx. 1.46, not 1.73 I use 1.46 as my pitch factor for 12/12 (I seem to remember using 1.414 actually)

If you're that fat before you figure for waste and you then add 17% for waste, also fat, your definitely building in an inflated bid. Better to do the math right and then add overhead and profit afterwards in my opinion.

Or do like Mike does, and add overhead to your labor costs and profit after all your "hard costs" are calculated. imho.

In the example given: 30X33 using a pitch factor of 1.73 yields a roof surface of about 17 sq. Using a pitch factor of 1.414 yields a surface of about 14 sq. That is a significant difference. Very significant. Maybe your tables are trying to include a waste factor in the 1.73 Couldn't say but it sure seems like it.

Certainteed gave me a handy dandy little pitch finder that cost them a couple of cents to make. A see-through piece of plastic with the pitches printed in chevrons right on it. You have to look through it and match up the gable (or cross-section) with whatever pitch it is. Takes about five seconds. Agree with OS...seventeen per cent is way too heavy for just about anything. I learned early on to use up my pieces as I go or at least save them in stacks for whatever places emerge that call for them. (like hip ends for valley tips and such. If it's composition my equally handy dandy AJC(rookston) chopper can deliver useable pieces from waste material in the blink of an eye. We used to get three hip ends out of a single tab in the old 3-tab days just using a hook knife or our AJC hatchets. Waste not want not.

Also, we tend to repeat ourselves around here quite a bit. But, then, once you are sure of something that you've said your main options are either to keep quiet or to repeat it. As my mother once said to me, "I know you've heard it before but it's a good story, I like it, and I'm going to tell it anyway."

Mountains, The ONLY way that all of us learn on this forum is by making mistakes on our own (I have made hundreds in my lifetime) or hopefully learning from other mistakes. Normally for me, it is what I found out AFTER I was sure that I knew everything that made a difference in my life. It is a shame that people get the impression that they are being made fun of on the forum for asking questions. That is certainly not what I try and do.

I do notice that a lot of people will try and make everything seem quite complicated when most things are actually quite simple. You can google to get the charts for the multiplication factors of the different pitches. Like the guys said, the charts are no good unless you have the correct pitch. The waste factor is another kicker. 17% to me would be a REALLY cut up roof. On the other hand, if you have both hips and valleys, what you cut off from a valley will fill in a hip and vice versa. That will take the number of shingles wasted down, thus lowering the percentage. Even on an Eagle view, they will give you the actual and then some various different numbers depending on what you want to plug in for a waste factor.

Since you say you need the work, I hope that you get it. I hope even more that you make enough money to make it worth your while.

What really irks me are the people that come onto this forum and start "Phishing" by posting some inane garbage that is supposed to be "educating" us professionals. To that, I would tell them to expect to be crucified. We will have fun doing it too. IF you are looking for information and advice however, we are more than willing to share. Thank you for having the courage to ask, Good luck.

I do the same twill .it's funny that the adjusters measured by setting it on the shingles and the average would be almost 3 squares .

the formula works just make sure the pitch finder is laid on the rafter or on the plywood not on the shingles.

Thanks for the reply old school. it is a 12/12. And I do know the the roof area is bigger that the footprint. I have never used a formula before. So I'm a little unsure if this really works. I really want and need the work so I don't want to be over or under squares ya know? Thanks again old school iv seen you posts many times and respect your opinion. I don't usually post things on here cause some guys make you feel stupid if you don't know how to figure things. But anyway thanks again.

How close do you want to get? Is it 12/12? You know that the roof area is greater than the foot print. You know that you have to add for the waste! 17% should do for that. If it is 12/12 and the foot print of the building is 20 squares, the rafter length is 1.41 of the run. That would give you 28.2 squares. If you multiply that by your 17% waste factor that would be 33 squares. Is that close enough?