Using a charcoal BBQ, how far should I be away from the house?
It really depends on the material of your house and the height of the overhang. 

In one extreme, if you have a brick house with no overhang you can be almost right up against it. 

Vinyl siding and/or 9' overhang is the other extreme. You should probably not be within 10' of vinyl siding. 

Somewhere in the middle is wood siding which probably will not burn but you might get paint bubbling if you are within 3'

As a general rule you don't want to be under a 1 story overhang which will hold heat and any sparks in.