figuring quantity of roof sheathing

[cwarn]

Hello. I am trying to get together a materials list to get a lumber bid for a house I am going to build. The roof is giving me a little trouble.
How do you estimate the number of sheets for a given roof? I looked at the calculator on this site but the roof I am working on is not square. :( I am looking at a hip roof on the main section with a couple gables off the front and another hip coming off the back in an "L". How do you account for these extras? I know there have to be different formulas for the various pitches, how or where can I find them to run different scenarios with roof height?
Thanks a lot.

[Rich]

What pitch roof do you have?
Let's assume you have a 6/12 pitch
6/12 (square that) add 1 and take the square root of it. = 1.12
That will give you the slope factor for your roof. Now do a takeoff of what the total horizontal square footage is including the overhangs (plan square footage). Multiply that by the slope factor and you'll have what you need. To get closer you'll need to account for the overhangs on any dormers too.

[cwarn]

Thanks Rich. I am probably going to go with an 8/12 pitch but I wanted to be able to figure it different ways. Your formula is exactly what I was looking for. Should I also add a certain percentage for waste and such or just figure on that number?
Thanks again.

[Cole]

10-15% waste for a complex roof.

[cwarn]

Thanks Cole. That helps me out a lot. Did I mention that I loved this site?

[grumpydasmurf]

Personally I measure the roof piece by pice then I get the squares, then I multiply by 3. (3 sheets per square).

When it comes to dormers, I first measure the elevation as if the former isn't there, then I add one half of the dormer roof. This is fairly accurate.

I would say 15% waste is excessive but it's better to err on the safe side. I usually add 5% for waste to a typical roof and 10% for a cut up roof.

[Cole]

I would say 15% waste is excessive but it's better to err on the safe side

Grumpy I usually never add more then 10% but I threw that number out there to cover my own ass, cause I dont know what his roof looks like :wink:

[Dragon]

I just do the geometry and add 10%

Thank you Pythagoras.

[grumpydasmurf]

I just do the geometry and add 10%

That's what I said ;)