We recently purchase a house which has an 8'x12' covered porch and I would like to place the pergola to the side of it to increase the shaded area in our backyard. I will be building a 16'x12' pavestone patio next to the current cement patio and would like to build the pergola over this (I would build the pergola first of course and then do the patio). The pergola will be attached to the house via a ledger board on the fascia of the roof and will then extend out with the furthest posts placed at approximately 15'. 2x6 beams would extend from the ledger board to 2x6 boards anchored on either side of the posts, and then the top beams would be 2x2s. You can see below to see what I am thinking of. My question is, with that span do I need another 2 posts in between the house and the outer posts (as shown in the image below) to prevent sagging, or will just the 2 posts be enough? Thanks!
Here is what I am thinking of:
this seems to be a little small here - here's the link to the regular size picture for more clarity: