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02-26-2010, 09:31 PM
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#1
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Pro
Trade:
Framing
Join Date: Jan 2010
Location: Toronto
Posts: 318
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Tough one?
Is the total rise to the top or bottom of the rafter? Is the unit rise to the top or bottom of the rafter?
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02-26-2010, 09:44 PM
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#2
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Pro
Trade:
carpenter
Join Date: Apr 2009
Location: Kirkfield,Ontario, Canada
Posts: 1,451
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First off I'd recommend the book - Construction Geometry, by Brian Walmsley, you can buy it at Lee Valley. An excellent book for construction geometry. He will explain everything you need to know.
To give a short answer to your question - picture a triangle from the outside of your plate to the centre of the total span, and then to the height designated ( 4/12,6/12 )
This is the geometric triangle of the roof, or "line length". So your actual rafter length will be from the outside of the top at the birdsmouth drawn in a line along the rafter at that point on the rafter to the centre of the
ridge.
Some guys bring that line at the outside plate verticle to the top of the rafter. Now the length can be measured on the top of the rafter to the centre of the ridge.
It's hard to give a visual of what's happening with just words. Anyone here got a cad drawing you can show him?
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02-26-2010, 09:48 PM
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#3
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Pro
Trade:
Framing
Join Date: Jan 2010
Location: Toronto
Posts: 318
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Quote:
Originally Posted by katoman
First off I'd recommend the book - Construction Geometry, by Brian Walmsley, you can buy it at Lee Valley. An excellent book for construction geometry. He will explain everything you need to know.
To give a short answer to your question - picture a triangle from the outside of your plate to the centre of the total span, and then to the height designated ( 4/12,6/12 )
This is the geometric triangle of the roof, or "line length". So your actual rafter length will be from the outside of the top at the birdsmouth drawn in a line along the rafter at that point on the rafter to the centre of the
ridge.
Some guys bring that line at the outside plate verticle to the top of the rafter. Now the length can be measured on the top of the rafter to the centre of the ridge.
It's hard to give a visual of what's happening with just words. Anyone here got a cad drawing you can show him?
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Is that supposed to help with the total rise and stuff..it sounds like your talking about rafter length.
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02-26-2010, 10:03 PM
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#4
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ubenhad4
Trade:
concrete framing and siding
Join Date: Jan 2010
Location: Central Oregon
Posts: 156
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Dude youve been here before. Unit of rise is just that. Rise per given unit usually inches of rise per ft. Does not mater if your on the bottom or top of the rafter.
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02-26-2010, 10:05 PM
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#5
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Pro
Trade:
Framing
Join Date: Jan 2010
Location: Toronto
Posts: 318
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Quote:
Originally Posted by ubenhad4
Dude youve been here before. Unit of rise is just that. Rise per given unit usually inches of rise per ft. Does not mater if your on the bottom or top of the rafter.
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I know i know but wouldn't it matter?
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02-26-2010, 10:05 PM
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#6
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Pro
Trade:
carpenter
Join Date: Apr 2009
Location: Kirkfield,Ontario, Canada
Posts: 1,451
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Quote:
Originally Posted by FramingPro
Is that supposed to help with the total rise and stuff..it sounds like your talking about rafter length.
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Rafter length is determined by the rise and run. Better buy that book.
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02-26-2010, 10:08 PM
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#7
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Pro
Trade:
Framing
Join Date: Jan 2010
Location: Toronto
Posts: 318
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Quote:
Originally Posted by katoman
Rafter length is determined by the rise and run. Better buy that book.
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I know that..I layout my rafters with my square but im just looking for a way so i can calculate the ridge height if im making a rake wall,if im not i just nail a pair of rafters and lift the ridge until the plumb cuts fit perfectly
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02-26-2010, 10:08 PM
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#8
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Pro
Trade:
Remodeling
Join Date: Oct 2007
Location: Northwest Connecticut
Posts: 1,619
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If you haven't had Geometry in school yet,pay attention as a lot will apply to this profession!
__________________
There is no warranty, expressed or implied, as to the accuracy, reliability or completeness of furnished data.Information gathered here may be for the sole purpose of entertainment.
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The Following User Says Thank You to oldfrt For This Useful Post:
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02-26-2010, 10:18 PM
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#9
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framer
Trade:
framing
Join Date: Feb 2007
Location: S.E. mass
Posts: 154
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do your rise per run calcs then add the HAP, that will be the top of ridge above your plate height.
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02-26-2010, 10:19 PM
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#10
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Pro
Trade:
Framing
Join Date: Jan 2010
Location: Toronto
Posts: 318
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Quote:
Originally Posted by steves
do your rise per run calcs then add the HAP, that will be the top of ridge above your plate height.
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so if i have a 12:12 pitch and 48" run and a 3 inch HAP ill have 51" to the top of the ridge?
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02-26-2010, 10:19 PM
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#11
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Pro
Trade:
Licensed Electrical Contractor and Remodeler
Join Date: Sep 2009
Location: Chicago Suburbs
Posts: 3,427
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Framing "pro" are you serious? A tough one?
If you are having trouble with rafter math on a common rafter, what are you going to do about deducting half the thickness of the ridge, and figuring overhangs? What about hip rafters?
Buy the book!
I can only hope that framerman and loneframer dont notice your thread.
__________________
220...221...whatever it takes!
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The Following User Says Thank You to rselectric1 For This Useful Post:
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02-26-2010, 10:21 PM
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#12
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Pro
Trade:
Framing
Join Date: Jan 2010
Location: Toronto
Posts: 318
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Quote:
Originally Posted by rselectric1
Framing "pro" are you serious? A tough one?
If you are having trouble with rafter math on a common rafter, what are you going to do about deducting half the thickness of the ridge, and figuring overhangs? What about hip rafters?
Buy the book!
I can only hope that framerman and loneframer dont notice your thread.
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I dont anymore..it was just the ridge height that was cloudy..i do overhangs and i made a small hip roof to try out the math
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