Parker Pergola Footings

A pergola is a light structure with a hard job. It has to stay square, stay plumb, and stay put through wind that comes across the open ground here without much to slow it down. None of that is decided by the timber or the hardware store bracket. It's decided by six holes in the ground and what we put in them.

Which means this is a soil job disguised as a carpentry job. What's under each post, how deep the hole goes, whether water can sit around the base, and whether the concrete is bearing on something that stays still through a Parker winter. Get that right and the structure is boring for twenty years. Get it wrong and you'll be shimming a post by the second spring.

The hole is the product

Here's what we're actually buying with a footing. Depth, so the bottom sits below the layer of soil that freezes and moves seasonally. Bearing, so the load spreads out onto ground that can carry it. Resistance to uplift, because wind wants to lift a pergola like a kite and a shallow block of concrete has almost nothing to hold it down. And separation from water, so the post bottom stays dry and the soil around the pier doesn't cycle wet and dry every time the sprinklers run.

That's why we drill rather than dig a shallow pit and dump a bag of mix in it. A drilled pier gets its uplift resistance from the weight of concrete plus soil friction along the full shaft, which only works if that shaft is deep and reasonably straight. A hole that flares at the top is a hole heave can grab.

The posts that lift are almost always on the sprinkler side of the yard. Water goes into the soil around a shallow pier all summer, freezes in November, and the pier rides up on it. Nobody blames the sprinklers.From the crew lead on these jobs

Where the water goes around a post

Soil that swells needs moisture to do it, so managing water around the pier does half the work. On a subdivision lot in Stonegate or Clarke Farms, the water source is usually irrigation and a downspout, both of which are fixable. We ask homeowners to move spray heads off the post locations, and where a pergola sits at the low point of a lawn we'll talk about regrading a few inches before we ever drill.

On wooded acreage the water arrives from uphill and it arrives all at once during a melt or a storm. That calls for a different answer: piers carried deeper, sometimes a shallow swale routing runoff around the footprint, and a gravel collar at the surface so water isn't pooling right against the concrete. Same structure, different plan for what's underneath it.

Four kinds of ground under a Parker post

Timing the holes around the season you want the shade

Backwards planning works best. If you want to sit under it in June, the footings should be in the ground by early spring, because the pergola build follows the concrete and lumber lead times have a habit of stretching. We can drill and pour piers in most winter conditions using heated mix water and insulation over the tops, so a February footing package to support an April build is entirely doable.

The season we avoid when we can is the muddy stretch after a big melt. Saturated ground makes a clean hole hard to keep open and makes equipment rough on a lawn. Late summer and fall are the easiest months.

What goes into each hole, bottom to top

• Hole drilled to design depth, sides kept clean, bottom cleared of loose spoil
• Bearing checked at depth, and the hole taken deeper when what we find calls for it
• Reinforcing cage set with cover all around, held centered rather than leaned against a side
• Concrete placed in one continuous pour, consolidated as it goes
• Post base hardware set to layout while the concrete is plastic, checked square before we leave
• Top of pier finished above grade with a slight slope so water sheds away from the post
• Backfill compacted in lifts, spoils spread or hauled, and the area raked out