Decks, Patios, Porches and Docks - Pergola Posts

My husband and I have a disaggreement on how to build our pergola. We have an existing patio slab and I would like to anchor the 6" x 6" pressure treated posts to the existing slab (about 3 - 4 inches thick).

My husband wants to put the posts in the ground which would involve removing the patio slab and then trying to dig 2 ft holes. Our problem is that here in Austin, TX we hit rock about a foot down so we will need a jackhammer to go further.

We are building a large pergola - about 12' x 24' using 8 posts.

Which way should we go?

Thanks!

I built a pergola not long ago, just a little smaller than yours. I anchored metal post bases to the existing slab and set the posts on them. You'll need a hammer drill and appropriately sized anchors (the ones I bought came with the right drill bit). Unnecessary perhaps, but I also epoxied the anchors into the slab.

A lot will depend upon the design of the pergola. If there is adequate lateral support to keep the structure from relying upon the posts for horizontal stability, then it can be anchored to the top of the slab. Pergolas have a vey high wind load, often laterally or in uplift. Normal concrete anchors are designed for shear strength, NOT pullout strength, so that is a factor as well.
I would not personally be comfortable with the posts anchored to the slab. (Here is my 14x20 pergola I am in the process of building. The posts are embedded in concrete 2' and tied to the joists through the facia, with two false posts to be added at the facia on top of the patio slab. I had to bust rock with a breaker bar for a foot and a half in each hole.)

http://72.41.69.75/pergola1.jpg

Thanks for the replies. And thank you Tscarborough for the picture. Your pergola looks great!

We are building the pergola based on the specs from the handyman magazine. The only difference is we are adding another section lengthwise so that is why we will have 8 columns.

Here's link:
http://www.rd.com/familyhandyman/content/17835

I would just hate to destroy the patio we have to build the pergola but I would also hate for it to be blown over.

Thank you for your comments.

That design is excellent, and will turn out great, BUT is has no lateral support on top. It relies on the posts for horizontal stability. To have that as a freestanding structure, you would need to create a "box" structure, which could be done with 45 degree kickers in 3 directions on each post or a decorative railing a foot or 2 below the main joists.

Thank you for the suggestions. That helps alot.

Hello,

Your project should require a building permit and I would bet that they will not let you anchor to the top of a 4" slab.

All is not lost though. You do not have to take the whole slab out. Cut out a square maybe 12" x 12" centered around your post. You can purchase a diamond blade for your saw. Don't try to cut too deep, it will take a few passes. You then will need to jack hammer the concrete within your cut out. Dig your hole, set your post. Leave the concrete low enough so that you can fill in around the post with brick, tile, stone or any contrasting material.

In my area, those footings would need to be 4 - 5 feet at a minimum.

Mark

like dooer stated, this probably needs a permit. THAT will answer many of your questions -- you have to do it in a way that the permitting jurisdiction allows.

If I were building it here, I would have to have footings. Attaching directly to the slab wouldn't fly. I would be told how large the footings have to be, and the holes would be inspected before the concrete was poured.

I would be installing a standoff post or column base in the concrete, and attaching the wood post to that. I couldn't set the wood directly in or on the concrete.

A jackhammer isn't that big of a deal. Rent an electric one. You can use it both to break up the concrete once it is cut, and by changing to a spade bit, use it to dig with.