Anchoring post to concrete.

[Todd Putnam]

Planning on building a pergola over our concrete patio and anchoring the posts to the concrete. Just got the patio extended and 3 corners have 6" footings the fourth corner will be on the original slab that is 4" thick. Planning on anchoring the 6x6 posts using a Strong Tie post base but am concerned about not having 6" footings on all corners. Any suggestions?

Strong Tie Post Base-
http://www.midlandhardware.com/848844.html?dfw_tracker=14396-848844&gclid=EAIaIQobChMInv7T_ZzN3AIVwSFpCh2X3gPTEAkYAyAB EgL6z_D_BwE

[Mike Ontko]

Any particular reason you're not going to tie one side of the structure to the house with a ledger? That would limit you to only needing to install two 6x6 posts.

For example: 390839

(the image was snagged off the Internet)

[Charlie Velasquez]

Any particular reason you're not going to tie one side of the structure to the house with a ledger? That would limit you to only needing to install two 6x6 posts.


But, would he then need to put those two post footings as deep as his house footings?

[Al Launier]

A pergola by itself is not a whole lot of weight to support, especially when there would be no snow load. I think Mike's suggestion is the way to go. Having the 6" footings is adequate for load support, yet where the footing is above frost level there may be some some minimal frost heaves over time, but that's usually not a concern for pergolas.

[Alex Zeller]

I've used these bases before but you must lay out the base exactly where you want the post to be. Also the post will hit the screw heads so I just use a drill bit to make a recess in the bottom of the post. They have four holes in them and a larger one in the middle. I usually use the four smaller holes so it can't twist. Usually the local stores don't have the bases you linked to in stock (for 4x4 yes but not 6x6). They are also not as gaudy looking. You should look at them in the store to decide. If the post isn't going to have good drainage (looking from your picture it doesn't look like they will be standing in water) and you're going to use pressure treated then you would want the stuff rated for ground contact. Around here the ground contact pressure treated 6x6 are landscaping timbers and not always the straightest.

https://www.midlandhardware.com/197018.html

[Ken Combs]

I like this one:
https://www.fastenersplus.com/Simpson-ABU44Z-4x4-Adjustable-Post-Base-Zmax-Finish?gclid=CjwKCAjw14rbBRB3EiwAKeoG_3DSyi3frLzN6 s5xYDtvm7eOdVOR5hvJfX6zN6ESyLh6ocGav8E5lxoCyJIQAvD _BwE
It spaces your post off the concrete and minimizes water damage. It also allows a little bit of fudge room in location as the anchor hole is slightly larger than the bolt needed.

Rather than the normal anchors, I use an anchoring epoxy by Sika and all-thread rod. That gives me a little more 'wiggle room' as I use a 5/8 hole and 1/2 rod.

I have some 6" square PVC posts attached to concrete by using 3 rods set in that and then filling the post with concrete. Really solid!

[Dave Cav]

We used these when building my pergola:

https://www.strongtie.com/retrofitpostbases_postbases/cptz_base/p/cptz

Very clean installation, only the black base shows and the end of the post is kept off the deck.

[Mike Ontko]

But, would he then need to put those two post footings as deep as his house footings?

I don't think so...though he should check with local building codes to be sure. Since this is just a pergola and not a deck structure, there's no substantial weight to carry on the two outside posts.

[James Biddle]

I don't think so...though he should check with local building codes to be sure. Since this is just a pergola and not a deck structure, there's no substantial weight to carry on the two outside posts.

I think the concern is that with the house structure below the frost line and the pergola posts above the frost line, the posts will move independently of the house, creating a stress point at the ledger board.

[Charlie Velasquez]

I think the concern is that with the house structure below the frost line and the pergola posts above the frost line, the posts will move independently of the house, creating a stress point at the ledger board.

Yes. I have not built a pergola in our area, but have done several decks. Our local AHJ requires attached decks to have footings at least below frost line, 48", and prefers as deep as the building's footing. The load is not a factor wrt depth, it is the ground heave.

Although ,... I assume the frost line in Iowa may be reduced in a few years because of climate change ....:rolleyes: ;)