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Old 01-12-2012, 01:36 AM   #1
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ridge height calculation


can someone check my working please? lgth 7500 x width 6050.wall height 3000. roof pitch 32.5.ridge beam 90 wide .made up of 2 x360 x 45 lvls(-15 mm notches both sides reduces wdth to 60)seat cut 90x57
tan 32.5 x 3025=1927 rise.theoretical ridge height 4927
hap 190-57=168
actual ridge height 4927+168-19(from 1/2 ridge)=5076 to top of beam?
i used an online calculator that gave 5095 as the height.did he allow the reduction in height?
using secant 1.1857 x run 3025 i get a rafter lgth 3587 -a 36mm shortening(from a 30mm ridge) giving me 3551 to the seat cut.im not worried about the overhang,i just cut oversize and chalk it to get a straight fascia.but the ridge has to be right as it weighs a ton.its supported by a saddle post made of 4 x 140 x 45 in a balloon framed gable end wall.any help would be gratefully received as i really dont want to blow this thanks

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Old 01-12-2012, 05:52 AM   #2
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What is this, mm's?
We use inches and feet here.
What is your span and what pitch do you want in feet and inches and I will tell you your rafter length and height of the ridge and seat cut, etc.
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Last edited by titanoman; 01-12-2012 at 05:55 AM.
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Old 01-12-2012, 01:16 PM   #3
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yes thats right.measurements are expressed in mm and the pitch is expressed in degrees.its called the metric system.we havent used feet and inches since the 1970s and most calcs are done using a basic school scientific calculator with trig function.
an 8 in 12 pitch has no relevance with the metric system and all the architects and engineers use degrees for roof angles now.
i guess im asking if someone could check my methodology to see if ive missed something.
it would be the same situation as if the pitch was not in the book or you couldnt find your tables or that guy you lent it to never returned it.
so anyway span 6050 roof angle 32.5 degrees.i put all the measurements in the previous post
heres hoping someone can help.thanks
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Old 01-12-2012, 02:22 PM   #4
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ridge height calculation


Oxbow,
Just curious, where are you located that metric system is the common measuring system? I'm guessing in the EU?
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Old 01-12-2012, 02:36 PM   #5
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hi bob ,im in new zealand.the usa is the only place ive found that still uses the imperial system of measurement although im told thats starting to change in some industries
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Old 01-12-2012, 02:45 PM   #6
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Oxbow, you are almost correct about the English system of units, I believe it is still used in Burma. Course they changed their name to Myanmar, and maybe now they use the metric system? Course you can still get a pint of ale in UK, and standard gage railroad track is still 4 foot 8-1/2 inches (width of a Roman road). And I bet you never heard anyone say

Give him an inch and he'll take 1,609.344 meters.

Also consider what a metric version of Whole Lotta Love by Led Zeppelin would sound like.
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Old 01-12-2012, 02:58 PM   #7
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what can i say? you have to love the interweb.one minute youre talking roofing then somehow it gets around to drinking beer.no wonder i cant get this job finished
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Old 01-12-2012, 03:04 PM   #8
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Quote:
Originally Posted by oxbow
yes thats right.measurements are expressed in mm and the pitch is expressed in degrees.its called the metric system.we havent used feet and inches since the 1970s and most calcs are done using a basic school scientific calculator with trig function.
an 8 in 12 pitch has no relevance with the metric system and all the architects and engineers use degrees for roof angles now.
i guess im asking if someone could check my methodology to see if ive missed something.
it would be the same situation as if the pitch was not in the book or you couldnt find your tables or that guy you lent it to never returned it.
so anyway span 6050 roof angle 32.5 degrees.i put all the measurements in the previous post
heres hoping someone can help.thanks
I don't use a table or anything. Just my brain.
Just tell me the span and the desired pitch and I'll set you straight.
I guess I could figure it out in
metrics, but that isn't the way we do it in America, and I'm an American.
I don't have a square in front of me either. That must be about a 5 1/2//12? Why?
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Last edited by titanoman; 01-12-2012 at 03:07 PM.
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Old 01-12-2012, 03:23 PM   #9
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titanoman sorry but we're just on different pages.what i have to deal with is a set of plans drawn how they are drawn using this system.its just the way it is and like all carpenters everywhere i have to make it work with how it is not how i'd like it to be
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Old 01-12-2012, 03:26 PM   #10
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Oh okay. Wished I could have helped you.

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Old 01-12-2012, 06:57 PM   #11
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titanoman,thanks i appreciate your effort.heres hoping someone familiar with degrees and metrics can help
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Old 01-12-2012, 07:11 PM   #12
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Quote:
Originally Posted by oxbow
titanoman,thanks i appreciate your effort.heres hoping someone familiar with degrees and metrics can help
Your welcome. Given a little time, I could convert and, check your figures for you.
But that would take a lot of math, therefore a couple hours.
With my luck, somebody that already knows the metric system would beat me back to you and all my efforts would be in vain.

Don't you have someplace you can chalk out what you have?
If it looks good on the floor, it'll look good in the air.
Also, I think you said you had a gable pocket to stick the ridge in?
So...the wall hasn't been built yet?
Which means you will need to chalk it out anyways for your plate and stud lengths, etc anyways?
Or are you trying to make a material list? It's all still on paper?
If the gable's already built...well, obviously there's nothing to check...?
Just curious.

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Last edited by titanoman; 01-12-2012 at 07:14 PM.
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Old 01-12-2012, 09:08 PM   #13
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yep, both the gables are up and i think i need to lift the beam because i miscalculated.i can simply put blocks in the pockets so all is not lost.i just want to feel confident that my rafters and birdsmouths fit.im pretty much doing this job by myself. theres no ceiling joists so ive got a mobile scaffold under the beam but i hate lifting timber up and down more than i have to.i found a site called blocklayer.com.au with a calculator that looks pretty good and agrees with my numbers.(he also does feet and inches)
im just going to go for it.wish me luck
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Old 01-12-2012, 09:13 PM   #14
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Quote:
Originally Posted by oxbow
yep, both the gables are up and i think i need to lift the beam because i miscalculated.i can simply put blocks in the pockets so all is not lost.i just want to feel confident that my rafters and birdsmouths fit.im pretty much doing this job by myself. theres no ceiling joists so ive got a mobile scaffold under the beam but i hate lifting timber up and down more than i have to.i found a site called blocklayer.com.au with a calculator that looks pretty good and agrees with my numbers.(he also does feet and inches)
im just going to go for it.wish me luck
Good luck and be careful.
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Old 01-12-2012, 09:16 PM   #15
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Just FYI we still mainly use Feet and inches in Canada too. Some metric though. I worked in a cabinet shop and we would get plans that had Metric for the cabinets but imperial for the site measurements, that was fun

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