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. :)

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!

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."

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.