Pergola Footings: Depth, Size and Anchors Sized for Uplift, Not Just Weight

Most advice on pergola footings borrows from decks, and that is where it goes wrong. A deck footing is sized for weight pushing down. Pergola footings have the opposite job: a pergola is light, its roof is an open grid, and the wind that catches it pulls the posts up. This guide covers how deep pergola footings must be, how big they are, how post bases and anchors fit, and what to do on a slab, on pavers or on a deck.

We are not your building department or your engineer. Where a number is our own design choice, we say so.

Why Pergola Footings Are About Uplift

A footing under a deck post resists a heavy downward load on soil. A footing under a pergola post resists a pull.

A light frame in the wind

Wind pushes sideways on the posts and beams, and it lifts the roof grid by suction. Our designer reads the wind pressures from the IRC components and cladding table, for walls in zone 5 and roofs in zone 2, with an exposure factor for open or sheltered ground. The default is 115 mph, and above 140 mph the designer stops and sends you to an engineer.

Suction acts on the solid part

An open grid does not catch wind like a solid roof. We count the suction only on the solid share of the grid, worked out from the rafter and slat spacing, and we let the structure resist 60% of its own dry weight. Both are our own choices, not code tables, and we have flagged them for confirmation by an engineer.

Weight is the cure

The cure is more concrete. A footing holds a post down by its own weight. We count 60% of the concrete’s weight against the uplift and enlarge the footing until that is enough. As an arithmetic example, concrete weighs 150 lb per cu ft, so a round footing 24 in across and 24 in deep holds about 940 lb of concrete, and 60% of that is about 565 lb. That is a worked sum to show the idea, not a design.

How Deep Should Pergola Footings Be?

Depth follows the same rule as decks, and then the pergola adds its own reasons to go deeper.

The 12 in minimum or the frost line

The footing bottom sits at least 12 in below undisturbed ground or below the frost line, whichever is deeper. Soil is assumed at 1,500 psf unless you know it is weaker, in which case DCA6¹ asks for a soils investigation. Our deck footings guide explains how to find your legal frost depth, and why a ZIP code map will not give it to you.

The small freestanding exemption

A 2015 rewrite of the deck footing section proposed by the North American Deck and Railing Association would have exempted small, light freestanding accessory structures of 600 sq ft or less from the frost rule. We could not verify that it applies to the 2021 code, so we do not use it. Our designer keeps the 12 in or frost depth. If your office accepts a shallower footing for a small pergola, that is its call.

Deeper than 60 in

A footing deeper than 60 in goes to an engineer in our designer. So does a footing wider than 36 in. These limits are our choice.

Pergola Footing Size and Concrete

Footing size comes from three checks, and the largest governs.

Soil bearing

A round footing is first sized from the load divided by the soil bearing, at least 6 in thick. It is also at least half as thick as the distance it projects beyond the 12 in pier, so the edge does not snap off.

Uplift

Then the designer grows the footing until 60% of its concrete weight is more than the uplift on the post. It picks the smallest volume that passes. For a tall, wide pergola in a windy place that can mean a big footing, which is the right answer and not a bug.

Why a bigger pergola can need a bigger footing

A larger pergola has more area for the wind to lift, and more post height to act as a lever. The footing grows with both. Taller posts also pull harder on the base. That is why a footing from one pergola’s plan should not be copied to another, even if both have four posts.

Concrete volume

Concrete is figured at 150 lb per cu ft. The plan lists the volume for each footing, so you can work out the bags. The concrete slab calculator gives bag counts for flat pours, which is a different job.

Pouring Pergola Footings, in Order

The pour is a one-way step, so check the layout before the concrete arrives.

Layout and digging

Set the post centers with string lines and check the corners square. Have underground utilities marked, then dig each hole to the planned depth, at least as wide as the planned footing. Take out loose soil so the concrete bears on undisturbed ground, and keep the holes the same depth so the bases end up level with each other.

Setting the bases

Place each post base on a template, a simple board with the bolt or base positions marked, so the spacing is exact. A base that is off by an inch makes the beam hard to fit, and you cannot move it once the concrete has set. Keep the standoff above the finished concrete, since the point of the base is to keep the post end off the wet surface.

Pouring, curing and checking

Fill the hole, work out the air, and check each base for plumb and height before the concrete stiffens. Follow the curing time on the bag before you load the posts, and brace any post that goes up early. Ask your building department when it wants to inspect the holes, since many offices look at them before the pour.

Pergola Post Bases and Anchors

A post base joins the post to the footing. It has to resist the same uplift the footing does, so choose it by rating, not by price.

Cast-in standoff bases

A cast-in base is set in the wet concrete and holds the post off the surface, which keeps the end grain dry. One example is the Simpson² Strong-Tie CBSTQ. From the maker’s table, which we read on October 26, 2026, it is rated at 2,680 lb of uplift on a 6x6 and 4,070 lb on a 4x4, with 485 lb of lateral load. That is one product and not a recommendation for yours.

Adjustable and retrofit bases

An adjustable base bolts to a slab you have already poured. An adjustable retrofit base does the same job as a cast-in one, but only if its rating covers your uplift. We found figures for one such base in store listings, and we did not use them, because we have not read the maker’s table. Look up the uplift for your base and your slab.

What the plan tells you

Our plan gives the uplift each post must resist. It does not tell you what any base can hold. Match the two yourself, using the maker’s published table.

Post anchors on a slab

For anchors into an existing slab, the rating depends on the concrete strength, the slab thickness and the distance from the edge. We hold no verified rating for any anchor, so we will not give a number. Follow the maker’s table and, when it asks for more than the slab has, cut through the slab for a footing.

Pergola Posts in the Ground or on Concrete

You can set the post in the soil, but you give something up.

Rot

DCA6¹ calls for pressure-treated lumber rated for above ground at UC3B and for ground contact at UC4A. A Simpson² Strong-Tie note from May 2025 says burying a wood post is not typically recommended because of rot, and a buried post needs UC4B at minimum.

Bracing and depth

A buried post without braces has to resist the wind by the soil alone. The IBC formula gives a deep hole, and our design, with no allowance for the doubling the code permits for isolated posts, needs about 62 in for an 8 ft 6x6. The hole is 12 in wide for a 4x4 and 16 in for a 6x6, at least 24 in deep. Those dimensions are ours. Whether to take the doubling is one of the open questions we have for an engineer.

Braces instead

With knee braces, the post can sit on a base and the footing handles the uplift and bearing. That is the choice for most pergolas, and the pergola attached to house guide covers the bracing for a freestanding frame.

Pergola Footings on a Slab, Pavers or a Deck

Your surface decides how the posts get fixed, and some surfaces cannot do it alone.

Existing concrete slab

A slab can hold a post base, but that is a question about the slab. Check its thickness and its edges against the anchor maker’s table. If you are not sure, cut a hole in the slab and pour a footing.

Pavers

Loose pavers are not a footing. They sit on sand and gravel, and a post fixed to them can lift the paver and the bedding with it. The posts need their own footings that go through the pavers. The paver calculator sizes the surface.

A deck

A pergola on a deck needs a load path to the ground that the deck was not designed for. The cleanest route is a footing for each post, through or beside the deck. We explain all three options in the pergola over deck guide.

Without digging

No-dig footing systems exist. Their uplift ratings are the thing to ask for, and we have not checked any, so we do not size for one. See the FAQ below.