I have a cabin in the mountains that has a "closed in" porch across the entire front. The outside wall is held up with 2x4 studs holding up a double plate. I would like to place some 8' windows on the front wall. I know that I need to add a header to do this, but since the porch hight is already low, I don't want to drop down too far. What size header can I place under the double plate to accommodate an 8' span?. I assume that the double plate counts for 3" of the total hight of the beam? I am also assuming that all I need at each end of the beam are 2x4s to hold it up. Is that correct?