Sql add days to a date taking into account the weekend

Hi,

I'm trying to calculate a due date for an order based on a set lead days parameter.
Ideally 'd like to do this in a function.

I have an order creation date.
From that I want to add 5 working days to it.
However, if part or all of the weekend fall within the 5 days I want to be able to take that into account

So an order placed on Thursday would be due the follwing Thursday.
i.e 5 working days plus 2 non working days.

Can anyone help me with the syntax.