Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Roofing/Siding

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 02-08-2011, 12:54 PM   #1
Member
 
Join Date: Jun 2009
Posts: 41
Share |
Default

Calculating roof square footage


I'm trying to calculate the total sq ft area of my roof. We plan to install a rainwater harvesting system, and I know the mfrs can do this for me, when designing their system, but I'm trying to get an idea before I start shopping what amount of area I have that will capture rainwater.

I can measure the horizontal dimensions. I've drawn sketches and taken pics. But I've got a lot of segments that are (I think the term is) hip roof, and one that (I think the term is) gable roof, and I don't know how to figure the pitch or angle, so I don't know how to calculate the lengths of the tilted sides of each surface.

I've got a saw protractor I can use to set saw angles from 0 to 60 degrees, and I can stand on the ground and hold it up and sorta eyeball the angles, but when I do that, and then I do the math, it just doesn't give me logical answers! I can do one side quite accurately, but the other sides don't come out right at all compared with the one I'm almost positive I got right, so I don't think I'm figuring the angle of the tilt or slope and therefore I'm not using the right tilted side lengths in my math.

Does this make any sense at all?

What can I do to get a better idea of how big the roof is?

tomseeley is offline   Reply With Quote
Old 02-08-2011, 03:46 PM   #2
Experienced
 
Jackofall1's Avatar
 
Join Date: Dec 2010
Location: Southern Michigan
Posts: 2,822
Default

Calculating roof square footage


Do you have excel, I could send you a program that I built.

Mark

__________________
When its all said and done there is usually more said than done
Jackofall1 is offline   Reply With Quote
Old 02-08-2011, 03:53 PM   #3
mem
Member
 
Join Date: Dec 2010
Location: Central Ohio
Posts: 224
Default

Calculating roof square footage


Post your photos and sketches--it would really help. I believe the only angle you will need to know is 90.
mem is offline   Reply With Quote
Old 02-08-2011, 04:43 PM   #4
Experienced
 
Jackofall1's Avatar
 
Join Date: Dec 2010
Location: Southern Michigan
Posts: 2,822
Default

Calculating roof square footage


You can measure the angle, by eye as you stated this will be close enough, measure the width, divide the width by 2, multiply half the width by the trig function "sec" in attached table, this will give you the angular length multiplied by the length will give you the area for that roof section.

I would consider an gable as intersecting with the roof at 90*

http://www.eugeneleeslover.com/USNAV...FUNCTIONS.html

Mark
__________________
When its all said and done there is usually more said than done

Last edited by Jackofall1; 02-08-2011 at 09:12 PM.
Jackofall1 is offline   Reply With Quote
Old 02-10-2011, 12:58 PM   #5
Member
 
Join Date: Jun 2009
Posts: 41
Default

Calculating roof square footage


JackofAll1

Thx for the help. Pls send your excel file to me at tomseeley @ hot mail dot com. I have MS Office 2010 so any version of Excel should work.
tomseeley is offline   Reply With Quote
Old 02-10-2011, 01:24 PM   #6
Member
 
Join Date: Jul 2010
Posts: 1,724
Default

Calculating roof square footage


Maybe I am reading something wrong, but I believe that you are incorporating too many non-essentials in the equation, and that you can do everything that you want on the ground, with no regard to roof slope, using only a tape measure. The amount of rain that will fall on your roof is the exact amount that would fall on the earth if your home were not there, so, again, unless I am missing something, all you need is the square footage of your home, and since you can only guess at the amount of a typical rainfall anyway, you could take that amount, and divide it by the number of downspouts that you have, in order to obtain an approximate volume per spout; the roof area, factoring in the pitch, is irrelevant. You probably already know the calculations, but there are 231 cubic inches in a gallons, so take your square footage, multiply it by 144, and divide by 231 to obtain the number of gallons per inch of rainfall.
DexterII is offline   Reply With Quote
Old 02-10-2011, 01:39 PM   #7
Member
 
Join Date: Jun 2009
Posts: 41
Default

Calculating roof square footage


well, duh..........

That makes such perfect sense, I'm embarrassed that I didn't think of it! You're right; I was definitely making it more complicated than I needed to!
tomseeley is offline   Reply With Quote
Old 02-10-2011, 01:46 PM   #8
Experienced
 
Jackofall1's Avatar
 
Join Date: Dec 2010
Location: Southern Michigan
Posts: 2,822
Default

Calculating roof square footage


Ok just sent that to you with a brief explanation on its use.

Dexter, you hit that one right on the nail head, sometimes you just can't see the forest through all them darn trees

Mark
__________________
When its all said and done there is usually more said than done

Last edited by Jackofall1; 02-10-2011 at 01:57 PM.
Jackofall1 is offline   Reply With Quote
Old 02-10-2011, 03:49 PM   #9
Member
 
Join Date: Jul 2010
Posts: 1,724
Default

Calculating roof square footage


As my dad would have told me, even a blind squirrel finds an acorn once in a while! Glad to help.
DexterII is offline   Reply With Quote
Old 02-12-2011, 06:13 AM   #10
Shut in w/o Home
 
seeyou's Avatar
 
Join Date: Dec 2008
Location: Lexington, KY
Posts: 696
Default

Calculating roof square footage


Quote:
Originally Posted by DexterII View Post
Maybe I am reading something wrong, but I believe that you are incorporating too many non-essentials in the equation, and that you can do everything that you want on the ground, with no regard to roof slope, using only a tape measure. The amount of rain that will fall on your roof is the exact amount that would fall on the earth if your home were not there, so, again, unless I am missing something, all you need is the square footage of your home, and since you can only guess at the amount of a typical rainfall anyway, you could take that amount, and divide it by the number of downspouts that you have, in order to obtain an approximate volume per spout; the roof area, factoring in the pitch, is irrelevant. You probably already know the calculations, but there are 231 cubic inches in a gallons, so take your square footage, multiply it by 144, and divide by 231 to obtain the number of gallons per inch of rainfall.
For this question, your answer probably serves the purpose well enough, but for properly sizing a gutter system, more factors come into play.

The statement I highlighted is true only if the rain is falling completely vertically which seldom is the case. One side of a gable will usually receive more water than the other due to rainfall angle, so the sizing needs to be related to roof plane area/slope rather than building footprint. A 12/12 roof next to a 6/12 roof with the same footprint will catch more water.

Here's a sizing guide:
http://www.guttersupply.com/file_are...ing%282%29.pdf
seeyou is offline   Reply With Quote
Old 02-13-2011, 11:12 AM   #11
Framing Contractor
 
Join Date: Apr 2006
Location: Caldwell, NJ
Posts: 1,758
Default

Calculating roof square footage


Quote:
Originally Posted by tomseeley View Post

What can I do to get a better idea of how big the roof is?
Go in the attic and measure the length of the rafters from outside plate t the ridge. Add for the overhang. You can't just guess at the length.

__________________
Joe Carola
Joe Carola is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Replace the roof or not??? Leaked only once when it snowed chasqui Roofing/Siding 10 04-13-2010 10:02 PM
Extend House Roof Over Back Deck Justahome Carpentry 1 04-03-2009 07:25 PM
Please help with the design of this roof jaymay75 Building & Construction 1 05-06-2008 09:44 AM
Flat roof - Rolled? - leaks Advice? JJ2001 Roofing/Siding 4 11-19-2006 06:17 AM
square footage chefjb98 General DIY Discussions 2 05-24-2006 02:54 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.