How much disk-space is needed to store a NULL value using postgresql DB?

Question

let\'s say I have a column on my table defined the following:

\"MyColumn\" smallint NULL

Storing a value like 0, 1 or something else should

Answer 1

It should need 1 byte (0x00) however it's the structure of the table that makes up most of the space, adding this one value might change something (Like adding a row) which needs more space than the sum of the data in it.

Edit: Laramie seems to know more about null than me :)