Kind of strange question

[Bryan Lisowski]

I have a metal shed that is about 10 years old and the roof has developed some small holes, my guess is from rust. As a temporary fix before building a new shed, I want to put a tarp over the roof. The shed is 10'x8'. The peak of the roof is about 12" above the wall. Obviously with the pitch of the roof it will add square footage to the area of the roof. How would you calculate the new square footage of the entire roof? I can't get on the roof to measure, so I guess I'm trying to find the area based on the rise and run of the roof. Anybody have a formula they can share?

Thanks
Bryan

[Tom Stenzel]

The answer is simple math: just split the roof into two triangles, calculate the area of one side then multiply by two.

My math teacher would have said at this point the rest is trivial, you're on your own.

I'm assuming that the roof has the ridge running the 10' length.

One half of the roof is 4' to the center, then a 1' rise. The hypotenuse of the right triangle is:

square root( 4 squared + 1 squared)

which works out to the square root of 17 for the length of the hypotenuse. My calculator spits out 4.123' for the length.

So each side is 41.23 square feet. 82.46 square feet for both sides.

Hope that's what you wanted. 'Scuse me now, have to rinse some chalk dust out of my eyes.

-Tom

[andy bessette]

... The peak of the roof is about 12" above the wall... I can't get on the roof to measure...

Since you're gjust guessing at the ridge height, and you can't get on the roof, I'd throw a weighted line over the roof and pull the weight up to the eaves on one side. Mark or knot it at the eaves on the other side and measure it once you pull it back off.

[Tom Stenzel]

Since you're just guessing at the ridge height, and you can't get on the roof, I'd throw a weighted line over the roof and pull the weight up to the eaves on one side. Mark or knot it at the eaves on the other side and measure it once you pull it back off.

Cheater.

:D

[Bryan Lisowski]

Thanks. I like the cheating method Andy posted. Will try that, since I just need a ballpark number.

[Bob Glenn]

The pyramids were built using just a string.

[Pat Barry]

Go to your local hardware store and buy a tarp. They only come in certain sizes. 8x10 is obviously too small. 9x12 might work. I'd buy the next bigger size.

[Yonak Hawkins]

The pyramids were built using just a string.

.. and a lot of labor, I assume.

[Chris Padilla]

And here we have a good reason for knowing a little bit of algebra! :)

[Bryan Lisowski]

It would be close with a 9x12' tarp, but I think I want a little more overhang, so I went looking and the best size is probably going to be 11x18. Thanks for the help guys.

[andy bessette]

...the best size is probably going to be 11x18....

We could have told you that would cover it. :)

[Tom Stenzel]

Thanks. I like the cheating method Andy posted. Will try that, since I just need a ballpark number.

An account by Thomas Edison's secretary:

"I went home and went to bed and left a call for about half-past five. I was up in the library again at six, and Mr. Edison told me to go over to the laboratory. The mathematicians were still figuring in the library, and they had been at it all night. I was told to get an incandescent lamp bulb that had not been used, one of the standard size, and to fill it with water; that I would also find in the same room a graduated glass, such a glass as druggists use, and then to bring the lamp bulb full of water and the graduated glass back to the library.

Edison took the bulb full of water in one hand and the graduated glass in the other, and poured the contents of the incandescent lamp bulb into the graduated glass. Of course there were marks on the graduated glass, and he knew exactly the contents of the incandescent lamp bulb on which the mathematicians had been figuring all night without coming anywhere near it."

It's traditional to cheat. Keep up to good work.

-Tom

[Bryan Lisowski]

We could have told you that would cover it. :)


My brain shuts down at midnight and sometimes doesn't restart until 11:59.