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Old 01-13-2012, 01:41 AM   #16
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ridge height calculation


Ridge height = theoretical height + rafters' height above the plate - ridge drop.

I checked your numbers and I found one mistake: 190 minus 57 does not equal 168, but 133. That 190 mm dimension in your rafters implies that your rafters are 11-3/4" wide, right? And your walls are 2x4s because your seat cut is 90 mm for the level cut?

Theoretical height = 3025 mm*tan (32.5d) = 1927 mm

H.A.P. = 190 mm - 57 mm = 133 mm

Ridge drop = 30 mm*tan (32.5d) = 19 mm

Height above the walls = 1927 mm + 133 mm - 19 mm = 2041 mm

I also get 3551 mm for the rafter length from the ridge beam to the plumb cut at the bird's mouth.


Last edited by abracaboom; 01-13-2012 at 02:30 AM.
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Old 01-13-2012, 03:25 AM   #17
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ridge height calculation


thanks abracaboom,you are right .the 190 is a rafter size that has a plumb cut of 225.minus 57 is the 168 hap.my mistake.i knew what i wanted to say but got confused.
the 90mm seat cut gives full seating on a 90 x 45 plate
HAP = 225-57 = 168
Height above walls would be
1927 + 168 - 19 = 2076
what do you think? go for it?
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Old 01-14-2012, 06:27 AM   #18
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ridge height calculation


Quote:
Originally Posted by oxbow View Post
thanks abracaboom,you are right .the 190 is a rafter size that has a plumb cut of 225.minus 57 is the 168 hap.my mistake.i knew what i wanted to say but got confused.
the 90mm seat cut gives full seating on a 90 x 45 plate
HAP = 225-57 = 168
Height above walls would be
1927 + 168 - 19 = 2076
what do you think? go for it?

If your gables are up, it seems to me like your dimensions are set. If you are hesitant, you might want to cut only two rafters and set them against the gables to see if they match at the height you calculated.
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Old 01-14-2012, 06:38 AM   #19
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ridge height calculation


I know what you mean about not wanting to lift lumber up and down any more than you have to. My wife and I built our log home by ourselves. Our roof is 12/12 pitch (45 degrees to you) so the ridge beam is way up there. Took a lot of scaffolding but we got it done.

I'm not a carpenter, or any other building trade, just an engineer and experienced DIYer. For my rafters, I drew everything up with AutoCAD and pulled needed dimensions and angles from there. Worked like a charm. I can't read a rafter square worth a hoot.

Talking about the metric thing, my wife called the other day and said she needed air in one of her car's tires but couldn't find a pump with enough pressure. She said the sticker on the door jamb said she needed 200! I told her that was kPa, which is around 32 psig in our world.
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Old 01-14-2012, 07:26 AM   #20
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ridge height calculation


Quote:
Originally Posted by mae-ling View Post
Just FYI we still mainly use Feet and inches in Canada too. Some metric though.
This is where I disagree with you. With the exception of perhaps your trade, of which I know nothing about, Canadians mostly use the metric system. School kids are taught kilometres and litres. They have no idea about miles and quarts
Food labels
Road signs and speed limits
Temperatures
Gas fill ups

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