Rafter plumb cut debate

D4np · Post by **D4np** » Mon Jul 30, 2018 8:23 pm

Hi everyone just a question I’m gonna throw out there and I’m looking forward to seeing The replies ...

Today I have been working on a squint roof .. I have Infilled the areas where the trusses meet with rafters ..

The trusses are a 40 degree pitch ...

What angle is the plumb cut ? I know how I did it but my friend has a app on his phone which , in my eyes , got the seat and the plumb cut the wrong way round .

Looking forward to your answers

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ayjay · Post by **ayjay** » Mon Jul 30, 2018 10:58 pm

D4np wrote:
Today I have been working on a squint roof ..

Can you define "squint roof"?

D4np · Post by **D4np** » Tue Jul 31, 2018 5:34 am

ayjay wrote:
D4np wrote:
Today I have been working on a squint roof ..
Can you define "squint roof"?

Dog leg roof - the type of roof is irrelevant

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ayjay · Post by **ayjay** » Tue Jul 31, 2018 7:17 am

D4np wrote:
ayjay wrote:
D4np wrote:
Today I have been working on a squint roof ..
Can you define "squint roof"?
Dog leg roof - the type of roof is irrelevant

It's relevant if I don't know what a squint roof is.

If I'm understanding dog-leg correctly, you were filling in the valley between the two sections and the plumb cut on the valley jacks will be 40°.

Can't really see how there can be a debate about it, a 40° pitch is a 40° pitch and the plumb cut will be 40° on all the rafters.

D4np · Post by **D4np** » Tue Jul 31, 2018 6:18 pm

This is exactly what I did and have always done but if you go on to any rafter calculating app or website and put in 40 degree pitch it will say the plumb cut should be 50 degrees . I saw a discussion on a screwfix forum and the responses were mixed. I was hoping to find someone who was going to say the plumb cut should be 50 degrees so that they could explain how they do it

https://community.screwfix.com/threads/ ... far.20017/

D4np · Post by **D4np** » Tue Jul 31, 2018 6:22 pm

ayjay wrote:
D4np wrote:
ayjay wrote:
D4np wrote:
Today I have been working on a squint roof ..
Can you define "squint roof"?
Dog leg roof - the type of roof is irrelevant

It's relevant if I don't know what a squint roof is.

If I'm understanding dog-leg correctly, you were filling in the valley between the two sections and the plumb cut on the valley jacks will be 40°.

Can't really see how there can be a debate about it, a 40° pitch is a 40° pitch and the plumb cut will be 40° on all the rafters.

Sorry me being a bit defensive too quickly ! So basically the building is 45 degrees see link

https://bit.ly/2OvuRCU

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steviejoiner74 · Post by **steviejoiner74** » Tue Jul 31, 2018 7:16 pm

When I’m cutting a roof the angles are not something I tend to ponder over too much as all my angles are on a scrap piece of timber after being worked out with a string line,spirit level and sliding bevel.
However if the pitch is 40 degrees then the confusion lies with angles on a mitre saw or circular saw being different(I’m not good at explaining this)
The 50 degree is what’s left to make a right angle and this is what I think you mean by the plumb cut being 50 degrees??

Btw I agree with ayjay. Plumb cut is always same as the pitch.

D4np · Post by **D4np** » Tue Jul 31, 2018 7:28 pm

steviejoiner74 wrote:When I’m cutting a roof the angles are not something I tend to ponder over too much as all my angles are on a scrap piece of timber after being worked out with a string line,spirit level and sliding bevel.
However if the pitch is 40 degrees then the confusion lies with angles on a mitre saw or circular saw being different(I’m not good at explaining this)
The 50 degree is what’s left to make a right angle and this is what I think you mean by the plumb cut being 50 degrees??

Thanks for our reply stevie . I did wonder if it was something to do with that because when using a mitre saw on 0 degrees it is actually cutting at 90 degrees ? Could this be where the confusion is coming from ?

I use a square and pivot so the angle lines up with the same angle as the roof then my seat cut is just square off of the 40 degree plumb line .

I actually e-mailed custom service of the app and he very kindly replied with this explanation - although I still believe it to be misleading as people like us who use the app are going to be marking and cutting the angle using a mitre saw or roofing square
———————-/—-
Hi Dan
Thanks for your interest in our roof app and if I'm getting your query correct, if the angle of the roof is 40 deg. Then the plumb cut which is the vertical cut is def. 50 deg. and the seat cut which is the horizontal cut which sits on the top of plate is 40 deg. I'm sure you must be just visualising it wrong, a roof angle of 40 means the rafter is angled at 40 deg from the horizontal plane, I hope my explanation solves your query but trust me the app is correct, happy roofing.
Regards
buildcalcs

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steviejoiner74 · Post by **steviejoiner74** » Tue Jul 31, 2018 7:31 pm

I did a 10 degree mono pitched roof last month and the plumb cut at the ledger certainly wasn’t 80 degrees!!

D4np · Post by **D4np** » Tue Jul 31, 2018 7:42 pm

steviejoiner74 wrote:I did a 10 degree mono pitched roof last month and the plumb cut at the ledger certainly wasn’t 80 degrees!!

Thank you , I’m not going insane !

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D4np · Post by **D4np** » Tue Jul 31, 2018 7:46 pm

steviejoiner74 wrote:I did a 10 degree mono pitched roof last month and the plumb cut at the ledger certainly wasn’t 80 degrees!!

Just put in the app your 10 degree roof and I’m afraid your wrong and it must have been 80 according to this

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steviejoiner74 · Post by **steviejoiner74** » Tue Jul 31, 2018 7:51 pm

yeah that’s where the app hasn’t been tested in a real world environment or been developed by someone that’s ever cut a roof. I’ve never seen any joiner use an app to work out roof angles

The seat cut is wrong on the app too

D4np · Post by **D4np** » Tue Jul 31, 2018 7:55 pm

steviejoiner74 wrote:yeah that’s where the app hasn’t been tested in a real world environment or been developed by someone that’s ever cut a roof. I’ve never seen any joiner use an app to work out roof angles

The seat cut is wrong on the app too

not wrong just the wrong way around ....

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steviejoiner74 · Post by **steviejoiner74** » Tue Jul 31, 2018 8:00 pm

See if you set a string line from the ridge to a stick nailed on the vertical(put a nail at top of overhang point and wrap line round this) you can get all the angles you need by laying a sliding bevel against the ridge,wall plate etc and mark them on a scrap piece of timber. Works for setting the hip as well which is a whole different ball game for angles.

Remember the ridge plates and wall plates are never bang on for level and this method takes away the need to know the angle

D4np · Post by **D4np** » Tue Jul 31, 2018 8:07 pm

steviejoiner74 wrote:See if you set a string line from the ridge to a stick nailed on the vertical(put a nail at top of overhang point and wrap line round this) you can get all the angles you need by laying a sliding bevel against the ridge,wall plate etc and mark them on a scrap piece of timber. Works for setting the hip as well which is a whole different ball game for angles.

Remember the ridge plates and wall plates are never bang on for level and this method takes away the need to know the angle

Love seeing and listening to the different ways to get the same outcome - however I have never seen anybody do that on site .. the app also gives the hip angles , do you recall any roofs and remember the hip angles so I can put it in the app to test ?

At the end of the day the app is good you just have to swap the seat and plumb cut angles around . Here is the details you enter to the app

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