Decks, Patios, Porches and Docks - patio header span

Hi, I need some advice for extending the roof of my house. I added a 13'x18' slab of cement to the existing patio and want to extend the roof to cover it. The 18' side will run parrallel to the house which has a 6''x14'' x18' header over the existing patio. I am usins 2"6"x 16' rafters. What I need help with is the header at the new end of the patio. I only want to use 2 posts to hold it up. They will be 4"x6" by what ever length. For the header I was planing on using a 4"x6"x 18' but a guy at the lumber yard said I would need another post in the center. Im thinking of using a 4"x10" now but dont want to start without being sure. Any opinions will be greatly appreciated

Before you start building, make sure you've got any and all permits needed. Around here, anything attached to the house is required to have frost footings.
If your new slab is just that, a slab with no footings, it will probably not be sufficient to carry the weight of the roof. The concrete would most likely be strong enough not to be crushed, but it may settle quite drastically from the roof's weight pushing down on the outside edge. It could actually tilt the slab.

Pecos

You can't span 16' with a 2x6 unless it is in truss form, you will need to use 6x6 vertical support every 8', and like Pecos said, your footings will need to be dug, filled to local frost specifications. Get the blessings of your local inspection department by making drawings with lumber dimensions so they can help correct maladies before you get started.

that new 18' header is going to need to be bigger. LVL would be the best way to go. 2 ply 2x12 lvl MINIMUM.