How to calculate roof height/slope.

[JJ1]

Hi,
I'm planning to build a shed, 8ft x 6ft with a pent roof. The front of the shed is 8ft across and the maximum height, from floor to roof needs to be 7ft at the front. I would like the roof to slope down towards the back with a 10 degree slope. Could anyone tell me please how to calculate the height that the rear of the shed needs to be to allow for the 10 degree slope.
Thanks,
Justin

 

[Bingy man]

I hate calculations but 10 deg is next to nothing. As long as the front is higher than the back by a few inches you won’t be far off your 10.deg . Other members will have the exact info you need..

 

[artie]

I'm sure there's a online calculator somewhere. But, if it was me I'd give it 12" over the six ft and forget about degrees.
Or, if you're using T&G just make the difference two or three full boards to save a lot of cutting.

 

[PerryGunn]

@artie is close enough, a 10 degree slope works out as a fall of 12.7" over 72"

Most references give a 1:80 fall for a (non tiled) flat roof - BS6229/8217 say that you should design with a 1:40 fall (just over 1.4 degrees) to allow for construction inaccuracies.

Even if you were to go for the 1:40 fall, you'd need less than 2" over 72"

 

[Sideways]

Slopes in construction terms seem more often expressed in terms of rise or fall over a given horizontal distance. Perhaps because the angles required are actually pretty small.

I just reroofed a single garage and corrected the slope of the flat roof for better run off. I noted the minimum 1:80 requirement and the very good advice to build for 1:40 in case some slope "gets lost" along the way.
I achieved 1:60, limited by how much I could raise the edge of the roof.

This drains perfectly well.
1:40 would drain faster so I agree, anything with more than 2" height difference front to back is going to work.
If you were to allow a huge margin for settlement and timbers sagging and consider 6" fall from front to back. That is I believe 4.8 degrees

 

[sawtooth-9]

Slopes in construction terms seem more often expressed in terms of rise or fall over a given horizontal distance. Perhaps because the angles required are actually pretty small.

I just reroofed a single garage and corrected the slope of the flat roof for better run off. I noted the minimum 1:80 requirement and the very good advice to build for 1:40 in case some slope "gets lost" along the way.
I achieved 1:60, limited by how much I could raise the edge of the roof.

This drains perfectly well.
1:40 would drain faster so I agree, anything with more than 2" height difference front to back is going to work.
If you were to allow a huge margin for settlement and timbers sagging and consider 6" fall from front to back. That is I believe 4.8 degrees

Sideways is correct, a 6 inch fall over six feet is 4.8 degrees.
If you want 10 degrees, the difference in height from front to rear is given by
X / 72 = Tan 10 degrees
This gives a fall of 12.7 inches - Are you draining rain or Snow ?

 

[clogs]

this is the one I use.......
https://www.calculator.net/triangle-calculator.html

 

[johnnyb]

whilst I'm not agin maths( jacob) I would draw this full size using sticks or strips then measure directly. or it's 1 inch in a foot and a half. I would go a few degrees steeper as they can tend to sag.

 

[JJ1]

Many thanks for all of the advice given. I shall re-read through all of the suggestions over the next day or two to gain a better understanding.

The slope will be to drain/collect rain water, as opposed to snow.