Irregular hip table

oz0707 · Post by **oz0707** » Sat Sep 25, 2021 5:15 pm

I've got goss' reckoner but can't remember it dealing with irregular hips. Are there any tables anywhere which give you the hip angle if for instance your main roof is 45 and end is 30 deg?
Or would the combinations of different angles be so numerous that a table would be to large?

Is it the case that you could add both standard hip angles and divide by 2 to get the irregular hip angle?

Obviously all assuming equal overhang and the hip not passing over the corner of wall plate.

ayjay · Post by **ayjay** » Sat Sep 25, 2021 7:17 pm

There's a calculator here, might be worth a try:-

http://www.timbertoolbox.com/Calcs/irreghip.html

oz0707 · Post by **oz0707** » Sat Sep 25, 2021 7:50 pm

Good website will have a play with it see what I can figure out

wes56 · Post by **wes56** » Sun Sep 26, 2021 11:27 am

Back in the day there was a book "Roof Cutting" by Marshall Gross. I think old Marshall was slightly doolally when he wrote the book. The book was littered with wrong calculations and advice, and some of the pics were well wrong too.
He couldn't give a simple explanation to save his life although perseverance often brought out good results.
Marshall claimed he wrote the book for his apprentices - if so, the poor creatures must have been driven out of their minds.
Having said that some of it is outstanding for anyone with low irritation levels and massive patience.
I constructed scaled models, and after a few weeks of giving up and then going back to the book and my model I reproduced a level eaves line on intersecting roofs with unequal pitches - all worked out mathematically.
In this difficult level eaves construction Marshall was spot on but the effort required has left scars.

oz0707 · Post by **oz0707** » Sun Sep 26, 2021 11:37 am

Having a play with it now. Think I will have to re learn trigonometry and TAN COS SIN the only one I remember is pythagoros.

I've got the Goss book Wes - I just use it for the quick reference tables on hip pitches and decreasing amounts for 600/400 centres etc Got the below figures from it this morning

Roof pitch / Hip Pitch
45 / 35.5
35 / 26.5
30 / 22
20 / 14.5

So then had a play with the calculator but the results indicated it wasn't as simple as adding both hip pitches together and dividing by 2. Also very surprisingly to me some combination of pitches result in a steeper hip than both sides/pitches of an irregular roof. I can't quite compute that in my head. These are the results (rounded to nearest .5 deg)

Roof pitch 1 / roof pitch 2 / Hip pitch (doesn't matter which way round 1&2 are)

45 / 30 / 25.5

35 / 45 / 23

35 / 20 / 34 - close to main roof pitch!

30 / 20 / 35! - steeper than either side of the roof!

Im sure there's a reason for that above would maybe have to draw it out for my mind to understand. I've not even got an irregular roof coming up it was just something I started thinking about. I last did an irregular roof a couple of years ago. It included a valley (/inverted hip) with vaulted ceiling below and I remember it frying my brain then! Got it done and it all worked out but was some serious head scratching going on in the middle of summer too. I follow a few guys on instagram who specialise in this stuff and it is just mind blowing to me. Fair play to them

oz0707 · Post by **oz0707** » Sun Sep 26, 2021 11:38 am

I had to double up my wall plate on the roof I did as your HAP changes so much with different pitches

wes56 · Post by **wes56** » Sun Sep 26, 2021 7:00 pm

I referred to "Roof Cutting" by Marshall Gross - ie. Gross. Not to "The Roofing Ready Reckoner" by Ralph Goss.