Centennial Pergola Footings

The kit is already in the garage. Four boxes of cedar or a pallet of powder coated steel, an instruction sheet with one vague page about post bases, and a patio poured long before you owned the house. That's how these calls begin, and the question never changes. Can we just bolt it to what's there?

Sometimes yes. More often no. The answer hangs on facts about that slab nobody can see from standing on it, and getting those facts takes an hour. This page is how we sort it out before anyone drills a hole that can't be undone.

What we need to learn about the patio you already have

Four things, in order. How thick it is, checked at an edge or with a small core rather than by tapping and nodding. What's underneath, because a slab over compacted base behaves nothing like one poured on loose dirt. Whether there's steel in it, which older patios frequently skip. And whether the concrete near each post location is sound, or has a crack running through it that becomes the failure point.

Across Southglenn and Foxridge we find original patios that have held up beautifully for decades as patios. Flat, solid, still draining away from the house. None of that says they can anchor a structure. A slab spreads weight downward across dirt. A post base asks it to resist a force pulling up at four small points, which is a different request entirely.

Uplift is the load that settles this argument

Everybody pictures the pergola pressing down. Down is easy. A modest footing handles timbers plus a wet spring snow sitting on them. The load that matters is wind getting underneath and trying to lift the whole thing, plus the prying force on each post as it pushes sideways.

Open slats let a lot of that pass through. Add a solid roof panel, a canopy, or a shade cloth stretched tight and you've built a wing. A gusty afternoon then puts real uplift on four anchor bolts. Bolts in a thin unreinforced slab don't shear off. They pull a cone of concrete out of the patio and take it along. Once that happens you're repairing the pergola and the patio both.

Ways to get a post onto a patio that's already poured

Sequencing it against the summer you want to use

Footings first, always. Drill the holes, set the bases, give the concrete a week, then build. Build first and you're boxed in by your own post spacing, and the hole you need lands exactly where the sprinkler line runs.

Spring and fall are the pleasant windows, though this work fits almost any month. We drill in winter, where the frozen upper foot is a nuisance rather than a barrier. What we won't do is pour into a hole holding water or set a base on frozen ground. Want shade by July? Call in spring. Planning next season? Fall drilling means cured concrete waiting when the lumber arrives.

Five things to settle before you buy the structure

• How many posts, and how far apart, since spacing changes what each footing carries
• Open slats or a solid roof, which is the difference between shade and a sail
• Attached to the house or freestanding on all four corners
• Anything getting hung from it later: a fan, a heater, a swing, string lights, a shade cloth
• Where the shade actually lands at three in the afternoon, not at noon
• What's buried under the patio, from irrigation lines to a gas run to the grill