Why do weatherboards on a door go vertical?

[Deansplit]

I'm building a shed under a staircase to a raised roof garden. Why do the weatherboards on a door go vertical when tongue and groove boards clearly prevent rain more if fitted horizontally?

 

[Jackrae]

By weather boards I assume you mean the style whereby the lower edge of one overlaps the board below it (if boards are installed horizontally)
If that is the case then weather boards shouldn't be installed vertically since the rain will migrate through the overlaps.
Doors should be made from tongue and groove boards, not weather boards
A door looks more pleasing to the eye if the boards used for its manufacture are installed vertically

 

[Deansplit]

OK thanks, I thought weather boards were t&g? Either way, so if using t&g for a shed door, they have to be horizontal to keep out water, yet they're all done vertically, as you suggest, look better. But surely they'd be leaking then?

 

[Jackrae]

Weatherboard are different from tongue and groove. It's the paint or oil that is used to protect the T&G that effects a vertical seal.

 

[r896neo]

You also have to be pragmatic about what water will do. Water running down a t&g joint is not under some magic pressure trying to force its way through the joint. In reality it will simply take the path of least resistance and gravity. Any tiny quantity of moisture making it across will evapourate.

 

[big-all]

if you use boards vertical they are structural and form the equivalent of the frame so no frame required just diagonals
it also allows the cross members to be set up for hinges and the locks