I had a guy come out to quote me a price on a new pergola. He said that he couldn't attach 6x6 or 8x8 posts to my existing slab, but would have to pour new concrete.

Is this correct? I know there are base plates to be attached using concrete screws. Am I missing something?

Could be the thickness of the slab. He may not want to install load bearing columns on a 4" thick slab. I wouldn't either but he could saw cut below the columns and pour a thickened footing for bearing.

How big is the pergola? What height and materials?

Long and short, there is probably a way to do it without busting out existing area. Now without more information, I am not sure which route is the most cost effective.

i had a framer who was working on a new house next door build me a pergola on my patio. just on a small 4" slab. it's been there 7 years, no problems. this was just 4X4s though.

[This message has been edited by 62strat (edited 5/23/2012 8:44a).]

Is the existing slab the size of the pergola? Why not place the posts just outside of the existing slab?

10 feet tall red cedar pergola. 6 inch slab patio. I don't want to put the posts in my yard.

The right way would be to pour a pier with a bell at the bottom just out side of your existing slab. The depth and width will depend on the load amount the post will be carrying. Another option is to put the post on the existing slab and dig out underneath and pour a pier underneath.

There is no guaranty that your slab will not crack by using the second option so the contractor is just trying to prevent problems down the road .

Your 6" slab will have plenty of capacity to support to post, but it most likely will crack over time since most likely there is only wire mesh in the slab and not #4's @ 12 or 18" OC which would make it a structural slab that could be attached to without any issues.

As a DIYer I would build it myself and anchor to the slab with 1/2" dia Simpson Titen HD anchors.