# Forum Home Renovation Roofing  how do I calculate roof slope for carport

## DNL

GDay all 
I am about to build my skillion roof carport which is 7m along the lenght of the house and 5.5m across the driveway. In the plans the maximum roof slope is 5 degrees.  
So how do I calculate the fall across the 5.5m.  :Confused:  
I seem to recall a builder telling me there needed to be a 20mm drop for every metre of roof length. This would mean the roof fall is 110mm. But I would like to know how it is calculated so I don't exceed the 5 degree slope. 
cheers and any advice - formulas and explanations greatly appreciated.
Dave

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## Bloss

Go to this site - sure to be a calculator for what you want: http://www.blocklayer.com/Roof/  :2thumbsup:

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## WACanetoad

5   degrees works out to 88 mm rise per metre run so the rise over 5500mm is 484 mm

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## bpj1968

Don't forget there is also a minimum drop for different roofing iron

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## WACanetoad

I think if you read your plans you will find it say minimum fall. For custom orb the minimum is 5 degrees and for trimdeck it is 2 degrees minimum

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## DNL

cheers fellas 
WACanetoad....I found detail on the Lysagth web site which indicates trimdeck has a minimum 2 degree slope or 1:30 fall. On 5.5 metre this comes out to 183mm fall. My rear verandah was 1:50 and it floods off. Its not trimdeck but similar with a larger profile. I think I might adjust to 1:50 as this is a 110mm fall and will work just as well. 
regards and thanks for responses.
Dave

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