I build pergolas out of lumber ... the 4x4 posts in the frost zone go 40 inches deep. dig the holes, make and attach the 4x4 crosspiece [use 2x12] and insert the two 4x4s in the holes with the 2x12 attached [bolt them] , level and rock the bottom 18 inches of the hole [so no water pools] and the fill the rest of the hole. I use bagged concrete and top it with soil. mine have been in the ground 30 years.

just saying.

I had a pergola built from four old porch columns I had saved. Also thought I could have them attached directly to the pergola's wooden "floor" without putting them in the ground. Well, it lasted about seven years then blew right over during a strong wind storm. The top was too heavy also and contributed to the fall. It's been a long time now, and I never got around to having it rebuilt - the proper way. The top is still down there, laying down on the floor to help keep it from rotting. Sweet peas have grown and entwined themselves through it.

Right after build, in 2014 before the top was painted white as well.

After storm, in 2021:

We did bury the footings, and we bought those at Home Depot. We already had a cobblestone pad the right size for the floor, and so we only had to remove a few of the cobblestones, bury the footings, and then we were able to proceed.

OK, I understand what you did now. I’m wanting to place one on our terrace where the flagstones are cemented together but it appears that’s not ”best practice” without a dug footing. Drilling into the rock would probably split the rock. And, digging a footing would require busting and removing rock to dig the footing.

@schoolhouse_gwagain, what were your columns made of? Were they solid? The pergola we’re looking at has 8 x 8 solid wood columns.

My columns were re-purposed wooden porch columns from my front porch (after two separate column replacements (in other words, porch only has two columns). They were old to begin with, and I was advised not to use them or install them the way I did but I wanted a vintage look. They were hollow.

New porch columns have the same shape as the old ones and are fiberglass, a product called "Perma Cast". Installed in 2012, and still looking great. I did paint them white and the paint has stayed on remarkably well. The base of each column is also fiberglass. The bases tend to get green stains from vegetation being too close, but that cleans off well IF one keeps ahead of it. I tend to be lazy until it gets really bad.

Instructions say "if used in free-standing applications, structured posts must be used inside column shafts" . My builder of the pergola did put some type of posts (2 X 4s?) inside but it wasn't enough to keep the columns strong because the posts were just nailed to the wooden floor. He only did as I wanted him to do.

If I rebuild the pergola I will use the Perma Cast. In 2012 two cost me $335. I bet it is three times that much today and I'd need four.

Here's one we did a few weeks ago. That's a 5 gallon plastic bucket. (the bucket is wider at the bottom). The patio slopes 4.5" in a 10' span. Ideally we would have taken out the patio first, repoured it....but ....we have renters in the property. It can be done at a later date. We lined up the bolt holes, put 3 ...12" threaded rods(all thread) into the cement when we poued it. The plate the gazebo leg bolts to, comes with the kit. Then wood was put into the hollow leg...and see the two vertical bolts to the left? That's a seperate 3/8" steel plate, shaped liked an "L"....to further stabilize each leg.

For right now...the renters have a gazebo. It can be prettied up at a later date.

@jrb451 - you have a gorgeous terrace!

It looks so nice, jrb!

Thank you Bluebell. We’ve been trying to come up with a solution for shading the terrace for 10+ years. I only wished we’d done this sooner but I was afraid we’d bust up the rock anchoring the posts. It turned out that the stones are on a 7” concrete slab. The contractor drilled in the mortar joints so not even a chip to the surrounding stone.

So nice!!!👍🏻

7 inches of concrete is a lot. That's thicker than many driveways and also thicker than some structural slabs for construction.

Did you have it put in? Why so thick?

Lovely job, jrb. It looks great.

That's very pretty! Lovely location with the beautiful trees out front.

^Yes, I meant to mention the trees…so pretty!

Elmer, we're not the builders. The home was built in 1965. The terrace is on a slope and maybe they wanted to ensure it stayed in place. We spoke to a previous owner before purchasing in 2004. They said it was their favorite place to live and the best constructed house they'd lived in. We remodeled in 2005.

The Pergola builder was expecting to find a 3" pad underneath the stones. The wood is custom cut Cypress. 8" true posts on 2x12x20 rafters.

Maybe the person who put in the pad owned a ready-mix company. I suspect the site preparation underneath and the support around the perimeter and beyond will affect a slab's stability on a slope more than the thickness of the concrete.

There's a serious amount of lumber on that structure too.

Enjoy it.

Your pergola is lovely jrb! I also love the surrounding landscape and gardening. Nicely done!