[brizzle]

Im doing research on a garage im wanting to build or have some built.

The garage im wanting to have foot print of 20 feet wide x 30 feet deep. Height what ever is needed not to exceed 20 feet at top.
Is there a caculator to determine 2nd floor floor space usable?
Loose some for stairs up to 2nd level.
How do you caculate how much you lose on the sides?


Thank you

 

[carpdad]

I would get an image of such a roof first, then play with numbers for compromise between the height restrictions and the look. Because of garage door hardware, best if the height is 8' for the headers. But other rooms can be 7.5' ceiling and such. Foam insulation, roof over roof construction, as much r value and free ventilation, all help with energy costs vs how much you need, therefore, rafter/joist thickness.

 

[Nealtw]

I would go with trusses, this one would give you 17 x30 less the stairs.

 

[Nealtw]

This one is 1 foot lower but you only get 14x 30

 

[House Designer]

This is what you are looking for:
https://www.wisconsintruss.com/files/WiscTruss_OrderGuide.pdf
It shows the usable room space for various sizes.